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Evolution, sex and dinosaur necks

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Matt Walker Matt Walker | 09:55 UK time, Tuesday, 24 May 2011

Diplodocus (image:Mark Hallet, PaleoArt/SPL)

Diplodocus, perhaps the most famous sauropod (image:Mark Hallet, PaleoArt/SPL)

They are among the largest and most fascinating creatures ever to have walked the Earth.

I’m talking about sauropods, the group of four legged dinosaurs that are almost instantly recognisable due to their long necks, each of which reaches out to a small head, and long tails.

Among the sauropods is the famous Diplodocus, and less well known, but even more remarkable species such as Argentinosaurus, which holds the record for being both the heaviest land animal ever, and the longest.

But what have these giants got to do with sex?

Well scientists are debating what exactly caused these huge reptiles to evolve their huge necks.

A recent theory proposed is that sex, or more accurately sexual selection, was the main driver.

The idea is that down the generations, male sauropods evolved ever longer necks to dominate rivals for the affections of females.

Dinosaurs are long dead, making it harder to test ideas about why certain traits evolved, and what they were adapted for. But evidence can still be brought to bear to analyse the different hypotheses.

For example, for much of the 20th century, sauropods were imagined to be water-loving beasts, which lived or spent much of their time in water, using their long necks as snorkels.

In the 1970s that idea fell into disrepute as multiple lines of evidence, since validated, showed sauropods to be mainly land-going animals.

That then led palaeontologists to imagine that sauropods used their long necks to reach huge amounts of vegetation – enough to yield the energy needed by their huge bodies.

A long neck, the reasoning goes, enabled Argentinosaurus and its ilk to graze plant material from a large “envelope”, from ground grasses to leaves in trees many metres high.

But then along came the sexual selection hypothesis, first proposed in 2006.

It argues that male sauropods that inherited a longer neck, caused by a chance mutation, would be more attractive to females.

The length of their neck would signal their virility and suitability as a sire.

Giraffe (image: Arup Shah / NPL)

Neck thumpers (image: Arup Shah / NPL)

A long neck could also have been used to wrestle competitor males, dominating them, just as male giraffes often joust by “necking" and "head clubbing" one another, with males with the longest necks and heaviest heads tending to win. Galapagos tortoises may also use the length of their necks to establish dominance.

Long necked males should therefore sire more offspring, on average, and pass down the long-necked genes, driving the trait through the population.

Just as palaeontologists argued over whether sauropods were terrestrial or aquatic beasts, they are now debating the merits of whether sexual selection or eating vegetation explains the long neck of the Diplodocus and others.

And the sexual selection idea has just been examined in detail, and dismissed.

Dr Mike Taylor of the University of Bristol and colleagues tested the arguments put forward to support the idea, and found them wanting.

Firstly, they say there is no evidence in the fossil record of a sauropod species that has males with relatively longer necks than females, or visa versa, which would be expected if it was a "sexy" trait.

While is impossible to witness whether extinct dinosaurs “necked” as giraffes do, their fossilised bones suggest they did not – they do not become any thicker to resist the blows, which would be expected, or show any signs of trauma associated with such behaviour.

There are a host of other more technical reasons for why a long neck wasn’t a sexy neck, Taylor and colleagues describe in the Journal of Zoology.

Their arguments are pretty convincing.

Such debates occur more often than you might expect, at least when it comes to sexually selected traits.

Indian peafowl (image: Phillipe Clement / NPL)

An eye for the females? (image: Phillipe Clement / NPL)

For example, there is still no firm agreement as to whether female peacocks find the elaborate trains of male peacocks attractive (length and eyespot number play a role, though precisely what is unclear).

There have also been similar debates about why giraffes have such long necks.

Indeed the proposal that the giraffe evolved its long neck as a sexual signal led to the proposal that sauropods do similar.

But in 2009, that hypothesis finally bit the dust after Professor Graham Mitchell of the University of Wyoming, in Laramie, US, and colleagues put the sexual selection hypothesis to the test by examining 17 male and 21 female giraffes.

They found if long necks were a sexually selected trait, they expected to find a number of things:

Long necks should be more exaggerated in males than females.

They should evolve to be bigger in size more than other parts of a giraffe's body.

They should confer no immediate benefit to survival, and may come at a cost.

Their results didn't support any of these propositions.

This refutation is similar to that by Dr Taylor and his colleagues. Sauropod necks aren’t more exaggerated in males than females, and they aren’t particularly costly.

Dr Taylor’s team make one final point.

There is no example, anywhere, of a type of four-legged animal, of which there are many species, that has evolved a single trait to be sexy. Crabs evolve big claws to show off, some flies evolve giant eye stalks, birds of paradise shake their sexy tail feathers.

But dinosaurs? Not likely it seems.

A sexy neck just didn’t get the reptilian juices flowing. 

Comments

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  • Comment number 1.

    I would be interested to know what led the exponents of the sexual selection theory to doubt the theory that long necks evolved to allow the animals to reach food high in the trees. I'm no palaeontologist, but the food theory seems both eminently viable and rather likely, so why is it being challenged by a far-from-solid theory such as the sexual selection one?

  • Comment number 2.

    A long neck means the need for a very powerful heart to maintain enough blood pressure to keep the brain functioning. This in turn pretty much proves the dinosaur was warm-blooded as no modren reptile has a cardiovascular system anywhere near powerful enough to maintain an elevated neck like this (reptiles are almost all low to the ground and horizontal to minimise the need to pump blood uphill).

    The argument I always accepted for the long neck (which because of its high energy needs is an evolutionary disadvantage that must have been offset by some great advantage) was that it was a counterweight for the enormous tail. The tail (which would have weighed several tons) swung hard into an attacker would be like being hit by an HGV.

  • Comment number 3.

    It always amuses me when people feel they have to ascribe a reason for a trait. There really does not have be one.

  • Comment number 4.

    #1. I'd guess 'evolving neck to reach high food' argument has been discredited as it would only occur if low lying food was in short supply. If there's all the plants you need at ground level you won't evolve a long neck (which requires massive energy expenditure... see my post #2) as there's no selective advantage to it. As far as I know plants weren't in short supply for these massive creatures. If you look at the artists drawing the sauropods are knee deep in plants.

  • Comment number 5.

    3. At 12:11 24th May 2011, Paul J Weighell wrote:
    It always amuses me when people feel they have to ascribe a reason for a trait. There really does not have be one.
    --
    Err... there is. Even our ridiculously useless appendix are an evolutionary relic from when we ate more raw plant material which doubtless in 10,000 generations will have vanished totally. You don't suddenly develop ten ton necks (which requires immense heart output) unless there's a real advantage to having one. Even penguins wings (which don't fly) make very powerful flippers under water. No animal i can think of has a major feature that does nothing.

  • Comment number 6.

    While being open to a mix of theories, the best to me seems to be that the long-necked dinosaurs became so as their primary food, pine trees, got taller.
    It was an arms race with the trees evolving to get away from their herbivore predators and necks getting longer to match (the nice soft tasty bits being at the tops of the trees). You can see their supposed food in the background of the artist's impression of a scene. I'm pretty sure that coprolite and other fossil evidence backs up the supposed diet for the beasts. The gizzard stones certainly were needed to mash up the almost indigestible pine needles and cones.

    Similar plant evolution happening in tandem with their predators can be seen here in the UK in Oaks (with their poison chemical deterrents for insects) and the Holly with its low-down prickled leaves changing to smooth with height, the turnover height matching the maximum height of their herbivores (cows and deer in this country, say).

    Since the demise of the dinosaurs 65ma ago, this now leaves vast tracts of the Earth covered in tall pine trees, but no large pine tree herbivores have evolved since to fill that niche. By the same token, the pine trees have had no evolutionary pressure to decrease in height either so they remain as they were, tall, thin, and poisonous to most creatures...

  • Comment number 7.

    Very interesting piece of research. I wonder though how many full skeletons they had to work from ... or even complete necks. In fact there's not much evidence in the fossil record to say anything with much certainty.

    @ Peter_sym ... it seems one of the reasons for dinosaurs being cold blooded is that it makes the extinction event theory more plausible.

  • Comment number 8.

    Hi there

    Nice write up but a few errors. Firstly the statement that "There is no example, anywhere, of a type of four-legged animal, of which there are many species, that has evolved a single trait to be sexy. Crabs evolve big claws to show off, some flies evolve giant eye stalks, birds of paradise shake their sexy tail feathers.": this is incorrect. What the paper states is that there is no example of a lineage of four-legged animals (which include birds of paradise, their front legs are just a bit modified) that has retained the same sexually selected ornament for a long period of time, geologically speaking. Regarding the giraffes' necks, there's good evidence that they are sexually selected, the debate is over whether sexual selection was the main driving force for their evolution - the most reasonable explanation in my opinion given the current evidence is that both feeding benefits *and* sexual selection played a part in the evolution of the long necks.

  • Comment number 9.

    Hi, Matt, many thanks for covering our research. You summary is excellent with just one misunderstanding which I'd like to correct.

    You report our work as saying "there is no example, anywhere, of a type of four-legged animal, of which there are many species, that has evolved a single trait to be sexy. Crabs evolve big claws to show off, some flies evolve giant eye stalks, birds of paradise shake their sexy tail feathers. But dinosaurs? Not likely it seems."

    It's not that we think four-leggedness acts against the possibility of sexual selection: I think this is a mistranslation of our statement "No single feature is sexually selected across any speciose tetrapod clade". We're not using "tetrapod" here just as fancy way of saying four-legged, but to refer to the great group of all terrestrial vertebrates and their descentants: amphibians, reptiles (including birds and other dinosaurs) and mammals (including whales and bats). Within that vast group, there is a large subgroup analogous to the sauropods where a single feature has been consistently sexually selected. So some birds (like peacocks) sexually select for an otherwise maladaptive tail, but they are a tiny group compared with sauropods.

    Mitya, I agree (obviously!) that the sexual selection hypothesis was badly flawed, but it was at least put together scientifically. It was proposed in this paper: Senter, Phil. 2006. Necks for sex: sexual selection as an explanation for sauropod dinosaur neck elongation. Journal of Zoology 271(1):45-53. doi:10.1111/j.1469-7998.2006.00197.x

    Peter_Sym, yes, the circulatory needs of a long neck and especially high neck are evidence in favour of elevated metabolism in dinosaurs -- something which is now near-universally accepted by palaeontologists. The idea of a long neck as a tail counterweight doesn't work at all, though: the longest-tailed sauropods (Diplodocus and similar) had relatively short necks, and the longest-necked (brachiosaurs and Mamenchisaurus) had relatively short tails.

    Paul J. Weighell, there absolutely does have to be a reason for any trait that persists across 150 million years on every continent!

    Peter_Sym again, there are plenty of reasons why high reach is advantageous even if food is generally plentiful: most obviously, those with the best reach will best survive during periods of drought, but there's more in the paper. (I won't go on as this comment is too long already.)

    By the way, the paper itself is available from
    http://www.miketaylor.org.uk/dino/pubs/taylor-et-al-2011b/TaylorEtAl2011-sauropod-necks-not-sexually-selected.pdf
    for anyone who wants to go deeper into our argument.

  • Comment number 10.

    Strangely wrote: "The gizzard stones certainly were needed to mash up the almost indigestible pine needles and cones." This idea was prevalent for a while, but it's been pretty comprehensively demolished by the work of Oliver Wings. Shame, I liked it :-)

    Wings, Oliver and P. Martin Sander. 2007. No gastric mill in sauropod dinosaurs: new evidence from analysis of gastrolith mass and function in ostriches. Proceedings of the Royal Society B 274: 635-640. doi:10.1098/rspb.2006.3763

  • Comment number 11.

    The logical, reasonable person sees that such debates are pointless. These animals were created and didn't "decide" to evolve longer necks.

  • Comment number 12.

    Sorry to keep posting. Two things.

    First, I made a catastrophic typo in my long comment above. When I wrote "there is a large subgroup analogous to the sauropods where ..." what I MEANT to say is "there is NO large subgroup analogous to the sauropods where ...". So I completely reversed the sense of my statement. Sorry about that.

    Second, AnotherVoiceInTheWilderness asked: "I wonder though how many full skeletons they had to work from ... or even complete necks. In fact there's not much evidence in the fossil record to say anything with much certainty." By happy coincidence, I blogged about this very issue just a few days ago. The answer is that there are very very VERY few complete sauropod necks known, and even the ones you probably think are complete actually are not. See the blog post in question at http://svpow.wordpress.com/2011/05/19/how-long-was-the-neck-of-diplodocus/

    (Why is this comment-editing box so stupidly small?)

  • Comment number 13.

    Matt, even if longer necks did get the juices flowing, (or big claws, giant eye stalks, or sexy tail feathers), this whole theory's based on the notion the females of such species were like demure X-factor judges who got to vote on the basis of best 'costume', best 'stage presence' and, ultimately, best 'overall performance', after which the losers'd shyly retire.

    What actually tends to happen, as anyone who's ever watched cats, pigeons, dogs, bees, ants, etc., mate is, far from being an animal world's equivalent of an elegant Arthurian style jousting tournament to win a fair lady's favour, a frenzied scrum occurs in which the females concerned're often lucky to escape not being raped to death.

    The long necks, big claws, zany patterning, etc, seem, if anything, intended to excite into a state of mutual frenzy the males themselves, basically turbo charging each others nuts into building up a maximal payload for the moment of discharge.

    Most rappers, for instance, use bling to intimidate their opponents, making them anxious they're doing better than them - the effect it has on girl's is a considerable second.

    Most girls dress to impress their friends and rivals firsts - guys're almost an afterthought.

    Homosexuality may even in part've evolved out of precisely this impress the competition routine.

  • Comment number 14.

    what about the fact that sauropods are huge, would need a lot of food and space, and so herds would need to be quite spaced out? long necks would allow visual contact to be maintained.

    COuld it not also be a-little-bit-of-each? does it have to be so elegant as to be a single reason, consistent over time? maybe the long neck offered a set of advantages which varied over time and actually made it more adaptable? spotting enemies, spotting mates, signalling, maintaining contact with the herd, reaching vegetation, if it could do a bit of each of these things it sounds like a pretty good adaptation?

  • Comment number 15.

    It seems strange to me that a lot of scientist are basing all there findings on the one theory of evolution. While many argue that the theory of evolution is pure fact, I think that it is a rather vague principle which may or may not be true.

  • Comment number 16.

    The chances are that it was a combination of sexual selection linked to resouce collection. A Long neck would have meant an animal could reach the best and most nutritional leaves on trees, and they would have been of the reach of smaller omnivores. So animals that have a better life expectancy become more desirable for females as the chances are that their offspring will have long necks and so will survive, hence there is a degree of sexual selection going on.

  • Comment number 17.

    Did these dinosaurs evolve their necks for one specific reason? Is it not more logical to suggest that their necks evolved from a number of contributing factors? they lived on a landscape that had tall trees, short trees, deep water, competition for mates etc would the neck not have evolved based on all the factors that make up their environment? I know that some genetic traits evolve in animals for specific reasons but would the random nature of evolution also not permit mutations caused by a number fo factors? Also could/should giraffe embryo's be genetically modified to grow a sauropd dinosaur? now thats a debate

  • Comment number 18.

    mburland: Sauropods weren't created and they didn't decide anything about their anatomy. Their necks were the result of evolution by natural selection; the discussion is about whether the fossil evidence indicates that selection was driven by food or by sex.

  • Comment number 19.

    mburland wrote: "The logical, reasonable person sees that such debates are pointless. These animals were created and didn't "decide" to evolve longer necks."

    Oh, dear. Do I really want to get sidetracked into this?

    Well, yes. I'll make one point and then step aside.

    mburland, posts like yours are an embarrassment to Christians in the sciences such as myself, because they indicate a complete lack of interest in HOW things happen -- which is what science is about. To say "God did it", while (I believe) true, is a statement of authorship, not of mechanism. It's not science. So to say that the sexual-selection vs. survival-selection discussion is moot because God made the animals in question is a category error. It's like interrupting an argument over whether The Mona Lisa was painted in oils or watercolours to say that Leonardo da Vinci painted it. It may be true, but it's not what we were talking about (and it sheds no light on what we are talking about).

    Here's another analogy. Most Christians believe that every human life is ultimately a gift from God; but we also recognise that the way that gift comes to us is via a specific natural mechanism involving sex, pregnancy and birth. Similarly, people who believe that the whole natural world is ultimately a gift from God still want to study and understand HOW it comes about.

    I hope this helpful, and not just more fuel for the flame.

  • Comment number 20.

    It was probably a combination of various factors driving the evolution of the long neck. Perhaps not sexual selection if the theories outlined here are correct, but most likely the advantage of reaching food and others we may not be aware of as we do not know the exact flora and fauna of their environment. I would like to throw one other potential factor into the mix - what about the advantages of seeing predators from a further distance or in amongst the undergrowth? It could also be an advantage to lift its head higher away from an attackers jaws, although I appreciate the neck would still be a feasible target to make a kill.

  • Comment number 21.

    A half-ton cow eating grass: munch munch, shuffle, munch munch, shuffle.
    A zillion-ton sauropod eating low plants: munch, munch, munch, while moving head in enormous arc to the left to cover a large strip, munch, munch, shuffle forwards a little, munch munch repeat going right, munch, munch. The energy expended is tiny compared to that of a sauropod-sized cow moving its bulk all of the time but the huge size gives more efficient digestion.

    Bucket-wheel excavators - the biggest land vehicles on earth - use this method of movement.

  • Comment number 22.

    What about Irish Elks? I thought their antlers were thought have got to such ridiculous sizes by sexual selection. "There is no example, anywhere, of a type of four-legged animal, of which there are many species, that has evolved a single trait to be sexy."

  • Comment number 23.

    CP, it's often been asserted (starting IIRC with John Martin's 1987 paper) that it's more energetically efficient for a sauropod to low-browse by sweeping out an area with its neck than to walk around as a cow does. But it's never been demonstrated, and that is paper I'd love to see. The energetic cost of maintaining a long neck -- holding it up, circulating blood along it, breathing through it, etc. -- would not have been negligible. My guess (and it's only a guess at this point, I don't have the background in bioenergetics to work it through) is that it might well be cheaper just to keep a short neck and walk around a bit more. If so, then the main utility of the neck must have been for HIGH browsing in particular.

  • Comment number 24.

    7. At 12:35 24th May 2011, AnotherVoiceInTheWilderness wrote:
    @ Peter_sym ... it seems one of the reasons for dinosaurs being cold blooded is that it makes the extinction event theory more plausible.
    ----
    I'd argue the opposite actually. Cold blooded reptiles like Crocodiles (which have remained more or less unchanged for 100 million years) survived whatever killed the dinosaurs quite nicely. The advantage of being cold blooded is that if you don't move much you don't need to eat much (some of the crocs in Africa eat two Wildebeast when the herds cross the river and just lie still for 6 months slowly digesting them waiting for the herd to come back again). A large warm blooded animal needs to eat a lot constantly to maintain its metabolism.

    I believe the dinosaurs evolved into birds argument (especially when you have intermediates like archeopterex) and without question all birds are warm blooded.

  • Comment number 25.

    Woody asks: "What about Irish Elks? I thought their antlers were thought have got to such ridiculous sizes by sexual selection." Yes, we mention them specifically in the paper:

    "If the long necks of sauropods had negative survival value, their retention across the whole clade is analogous to a hypothetical situation where the maladaptively long tails of birds-of-paradise are found throughout Passeriformes, or where the enormous antlers of the Irish Elk Megaloceros are ubiquitous in Artiodactyla. Instead, we see long-term progressive evolution of characters that have survival benefit, while sexually selected characteristics are subject to evolutionary "fashion" and tend to be much more labile."

  • Comment number 26.

    11. At 12:45 24th May 2011, mburland wrote:
    The logical, reasonable person sees that such debates are pointless. These animals were created and didn't "decide" to evolve longer necks.
    --
    Yup, created 60 million years ago. Mind you being logical & reasonable I have a problem with one tiny little point. Didn't god only create the earth 6,000 years ago? Bit of a timespan problem for you to explain there. I presume they all died out because they were too large for Noah to fit on the Arc during the great flood (which as that happened 4000 years ago was after the pyramids were built)

  • Comment number 27.

    Regarding the long necks argument, there's a difference between having a long neck (i.e. a long and mostly horizontal), as Diplodocus had, and a tall neck (i.e. a long but more vertical neck), as Brachiosaurus had. Having a long neck allows a creature to graze over a large area without having to move much apart from their necks. Having a tall neck allows a creature to reach high leaves.

  • Comment number 28.

    22. At 13:30 24th May 2011, Woody wrote:
    What about Irish Elks? I thought their antlers were thought have got to such ridiculous sizes by sexual selection. "There is no example, anywhere, of a type of four-legged animal, of which there are many species, that has evolved a single trait to be sexy."
    --
    I've seen one of those in a museum in Dublin. Due to the length of the antler a sharp twist of the neck would have the ends of the antlers whip through the air at incredible speed (in the same way that the end of a ten foot bit of rope whipped through the air by a man can exceed the speed of sound... a whip crack is a sonic boom). Any wolf getting caught by one of those antler ends would have been ripped wide open. Basically it'll be for either sex, feeding or fighting. Those are the three big driving forces. Sex is possible but without question those antlers are deadly. Modern red deer use their antlers as weapons to fight of rival males in order to get the pick of the girls so for them its both fighting and mating.

    As an example for teaching 'survival of the fittest' those elk are brilliant... whatever the reason for the antlers they flourised for a tiny period after the glaciers retreated but before the great pine forests regrew. Once you have thick forests the beast couldn't fit between the trees anymore and 'the fittest' was suddenly a more streamlined animal.

  • Comment number 29.

    Also, regarding the effort in keeping a long neck up, that can be built into the spinal chord, increasing strength but limiting vertical movement. There seems to be evidence (BBC Walking with Dinoasurs) that Diplodocus had very limited vertical movement of their necks.

  • Comment number 30.

    Thank you Mike for joining the debate... much appreciated.

    As to the efficiency of sweep or high browsing, I would have thought that would depend almost entirely on the soft-tissue structures. The giraffe, if I understand correctly, actually has to expend energy to lower the neck as the weight of the whole head/neck structure is counterbalanced by the massive ligament running up the back of the neck. I would have thought that such structures would define the 'neutral' position... and that may be high (indicating efficient high browsing) or low (indicating efficient sweep-browsing). All speculation of course... but in the absense of actually klnowing stuff, speculation is fun! :)

    PS. I'm fascinated by religion/science area, and while I disagree with your view Mike, it's great to hear an intelligent view of the matter from a religious scientist. It seems the people making the most noise are far too often those with nothing to say!

  • Comment number 31.

    Matt.

    I am surprised that you refer to male and female "peacocks". The animal is a peafowl; the male being a peacock, the female a peahen.

  • Comment number 32.

    #9 Mike - thanks for pointing out where I'd misinterpreted your comments about tetrapods - much appreciated. Fascinating research. Regarding the idea that traits have to be advantageous to persist: can you help me and maybe Peter_Sym and Paul J. Weighell out with some more insight? Can you explain a little about neutral traits or evolutionary drift (such as ideas that some traits can persist not because they are advantageous, but because they do no harm, or may even persist as they are somehow attached to another traits that are positive), and how these might not apply to a trait such as long necks that persists for such vast expanses of time?

    #13 aborky - thanks, you make a good point. Sexual selection is a difficult area, one scientists are still learning much about. Male competiton and female choice both play a role. Mike Taylor again may be able to help out out here, but female choice may actually play a much bigger role than previously thought. Some scientists (Prof Tim Birkhead at Sheffield University among others) feel that actually females may often be the dominant sex when it comes to sex selection, as females of many species control mating, and can even select which sperm they want to accept.

    #31 Todie23. You're right. Peacocks and peahens. No excuses there

  • Comment number 33.

    If sauropods evolved a long tail first, for defence, wouldnt they be totally out of ballance with a short neck. If they evolved big hearts first (because it wouldnt work the other way round), wouldnt this be very disadvantageous to have a enegry-hungry heart when it wasnt necessary.

    Why did the female that evolved the trait for preferring longer necks have such a advantageous trait that it got inherited by all future females? Isnt it better to preffer the standard length necks that already exist? A female with such a prefference may never mate.

    Thats the problem with all these non-technical story-like arguments. Biologists really need to take a hint from Physics.

    Apples fall to the ground because they evolved the trait to stick to the ground. The apples that flew off into space didnt produce any offspring. Hmmm...

  • Comment number 34.

    A couple of posts have suggested that long necks enabled better vision at a distance. Wouldn't good eyesight be a more efficient solution? How many other species have solved a similar problem by evolving long necks?

    In any case, the lack of communication would have had to have threatened the ability of some animals to survive, rather than just being a bit of a nuisance, in order to result in evolutionary change. As I understand the theory of evolution, change happens due to some genetic mutations, i.e. variations within the current range of type of the species, enabling more of the bearers to survive and have offspring, compared with those who do not have that mutation. If the survival value continues to be high, then over time that mutation or variation becomes the norm and all those without it die out. A range of differences within species, as well as features that were once useful but now have no function (e.g. human appendix), may persist while none of them confers a significant advantage or disadvantage.

    Just to make the point, as this is often misunderstood, evolution does not mean any species "gets better" or somehow in any objective sense "progresses". It simply means that it becomes better adapted to its environment. This point is often misunderstood when people apply the idea of evolution to social, economic or political areas. The corollary is that, if humans did indeed evolve from monkey-like creatures into the rather amazing animal that they now are, they must have gone through some incredibly tough times at some point, or points, in the past, and perhaps been on the edge of extinction - otherwise, no evolutionary pressure, and we could just have stayed the same like those crocodiles mentioned in a previous post.

    NB I am not a scientist, and may well not have explained this 100% accurately.

  • Comment number 35.

    Kiujhytg2 wrote: "regarding the effort in keeping a long neck up, that can be built into the spinal chord, increasing strength but limiting vertical movement. There seems to be evidence (BBC Walking with Dinoasurs) that Diplodocus had very limited vertical movement of their necks."

    Ah yes, that. You're referring to the work of Stevens and Parrish (1999) on their DinoMorph project which used computer modelling to simulate ranges of motion in two sauropods. At the time it was enthusiastically adopted, probably in large part because of WWD's adoption of that hypothesis. But it's badly flawed as we showed in a 2009 paper (by three of the four authors of the new sexual selection paper). We have a page with links to that paper and also to a lot of more user-friendly discussion, which you might find interesting: https://svpow.wordpress.com/papers-by-sv-powsketeers/taylor-et-al-2009-on-neck-posture/

    The short answer is that we don't believe any sauropod's neck was constrained to be held low and straight as depicted on WWD. (But not everyone agrees with us.)

  • Comment number 36.

    The long neck is because the head is so far from the body, simples.

  • Comment number 37.

    #32 My first degree was in genetics so I'm quite familiar with the idea of 'neutral traits' at least on one level. Blue or Brown eyes in the European population would be an example of something that persists because it doesn't really matter one way or the other. Blood groups would be another.

    I can't think of any major anatomical structures that can be classed as 'neutral traits' though. 5-10 tons of neck is there for a reason. It would be like me dragging a third leg around!

    Incidentally I'd call all canines 'dogs' & all 4 legged bovines 'cows' even when half of them are probably "bullocks". I wouldn't worry about the 'peahen' thing. Its one of these many instances when correct scientific language comes second to normal speech habit. I spend half my life culturing bacteria but will talk about 'bugs' or 'germs' when in non-scientific company.

  • Comment number 38.

    #33. The change would be very incremental over thousands of years: an animal with a 2 foot neck won't suddenly have offspring with a ten foot neck. They'll have offspring with a 2 foot 1 inch neck, then their grandkids will have a 2 foot 2 inch neck etc. It gives plenty of time for the tail to evolve at a similar rate. Ditto the heart. An Olympic athletes heart probably has twice the output my lazy beer drinking one does.

    #34 for a non-scientist thats pretty good. The only thing to add is that mutation is completely random and normally negative (when humans suffer mutation cancer or terrible birth defect is far more likely than better eyesight) and that 'the fittest' may not not be "fit" in the sense you think. Being overweight, half blind, asthmatic & flat footed is not 'fit' if you're on the Savannha and the lions are getting close. If however its 1916 and every other man in your village has just been sent off to die on the Western Front you get the pick of the girls and spread your genes.*

    *you can thank my 4th year biology teacher Mr Forsyth for that example.

  • Comment number 39.

    33. At 14:17 24th May 2011, Garry wrote:
    If sauropods evolved a long tail first, for defence, wouldnt they be totally out of ballance with a short neck. If they evolved big hearts first (because it wouldnt work the other way round), wouldnt this be very disadvantageous to have a enegry-hungry heart when it wasnt necessary.

    --------------

    I'm no scientist, but it wouldn't they evolve all of the traits simultaneously? A giant heart with no use would not be evolutionarily beneficial, so it would die out, as would a tail large enough to upend its owner or a neck so long blood can't get to the brain. So I imagine the ancestors of the sauropods would have had first short necks and tails and appropriately-sized hearts, then slowly grown larger and longer over generations. I'm pretty sure that's how this whole 'evolution' deal works.

  • Comment number 40.

    "The logical, reasonable person sees that such debates are pointless. These animals were created and didn't "decide" to evolve longer necks."

    No, they didn't 'decide' to evolve, they just *evolved*. It's over a very, very long time and involves much natural selection. The "logical, reasonable person" certainly wouldn't attribute this to creation, as a belief in creationism is the exact opposite of both logical and reasonable: supernatural and irrational.

  • Comment number 41.

    Things change over the years. At the moment there are no animals that look like they could evolve as big as a dinosaur. No bird, the size of a flying dinosaur, could get off the ground today, which suggests that maybe something like gravity has changed. If the force of gravity has increased slightly, it would explain the limit on animal size we have today. Who knows?

  • Comment number 42.

    "While many argue that the theory of evolution is pure fact, I think that it is a rather vague principle which may or may not be true. "

    And I suppose you think gravity is *just a theory* too, huh? Scientists treat evolution as fact because there is no doubt about it - it can be observed in laboratories in creatures such as flies that have short lifespans and is confirmed by the fossil records. It is anything but vague. Unless you'd like to offer us equally incontravertable evidence to the contrary?

  • Comment number 43.

    visa versa? Do you want cashback ?

  • Comment number 44.

    #41 Gravity certainly hasn't changed as the mass of the earth hasn't altered significantly. The really big dinosaurs are the 'sexy' ones that look good in pictures but most species were no bigger than dogs (or perhaps Turkeys might be a better example....). The largest animal ever known to have lived (Blue Whale ~200 tons) is alive today (just). Thats heavier than anything in the fossil record. Even an African elephant is about 4 tons. Diplodocus was 10-15. I'm about 14 stone and sadly you can find plenty of people 3 times my weight. It doesn't defy the laws of gravity you just need enough food to hand to maintain the bulk.

    The big flying dinosaurs weren't really flappers but gliders. They were big but not especially heavy. 14 stone of me under a hang glider is perfectly capable of jumping off a sea-cliff, soaring around on the thermals for a bit then landing back on the cliff. If I could get a few flaps in I'd be a pretty capable flier. The fossil record would suggest that dinosaurs evolved into feathered birds (there are plenty of 'missing links' showing features of both lizard and bird) as its a more efficient design.

  • Comment number 45.

    I have never understood these arguments about sexually driven traits.
    Does not natural selection require members of any species to find those
    features that are useful to be sexually attractive?

  • Comment number 46.

    How much water would a creature of this size need to drink to avoid dehydration? Surely there is a hydraulic limit to the length of the neck.

  • Comment number 47.

    Hi, I wonder if anyone could clear this up:

    "Sauropod necks aren’t more exaggerated in males than females, and they aren’t particularly costly."

    Can the fact that long necks aren't costly not be the reason why they aren't more exaggerated in males than females? By this I mean, if females bear no cost of having long necks, there would be no conflict of interest between them and the males over having them. Isn't 'sexual dimorphism' (more exaggerated necks in males) only expected when you have such a conflict of interest?

    For example, hip width in humans: Females do better with wider hips, but males 'prefer' narrower. Sexual dimorphism in hip width extinguishes the conflict.

    Therefore, if the long necks were sexually selected, whether for male-male battle or some female preference, the females wouldn't have shorter necks because they were of no cost to the females themselves. Would the long necks have to be costly to males in a direct sense? Or could they not still be sexually selected because longer necked males do better in battle and win more females.

    ta (great article btw!)

  • Comment number 48.

    Sexual selection shouldn't be thought of as an alternative to natural selection, it is rather an accelerator of the process.

    Even secondary features such as peacock tails are only possible because the bird has evolved well enough to have the access resources to grow it.

    If a long neck makes you more fit to life then selecting a mate with a longer neck is likely to make your offspring even more fit to survive any drought, or other environmental event, that would bring about natural selection in the population.

    I like the efficient ground browsing theory, it suits natural selection as well as browsing higher up trees as its efficiency would increase the sparser the ground vegetation became.

    Similarly, if warm blooded animals are evolved from cold blooded animals, then it will not always be right to set one against the other as if they are competing: where there was an advantage to evolve a warm blooded physiology then that is what will have happened. Birds need a high metabolic rate and a low body mass so becoming warm blooded is an obvious prerequisite. Crocs took an alternative path that suits their cold bloodedness better. It seems likely to me that increasing body mass is a way of improving the rate a cold blooded metabolism through retaining heat better by vitrue of the proportion of surface area to mass. Being big could have been an alternative to warm blood and fur, it fits the evidence of one stratergy following the other - dead Saurus's shoes.

  • Comment number 49.

    Charles L-G (45): Many traits whose evolution is driven by sexual selection are useless or even harmful. For example, the bright colours of many male birds make them more likely to be seen and eaten by predators than drab-coloured females. One theory is that bright colours, fine tails, etc advertise the fact that the male is healthy and therefore carries good genes for defence against disease. A female who chooses to mate with such a male might increase her chance of having offspring who are healthy enough to survive to reproductive age.

    It's often easier to understand evolution if you look at it from the point of view of a gene, not that of an individual organism. While a gene for bright coloration increases the chance of its owner being eaten, it also increases the chance of its owner mating and thus passing on copies of the gene to the next generation.

  • Comment number 50.

    *44 Yes but can 14 stone of you climb up a sea-cliff carrying a hang glider in order to glide.. Those people, who are three times your weight can barely walk and therefore easy prey to the odd passing T-rex. The largest birds today can only just take off and they are far lighter( max 48 pounds) than the flying dinosaurs. Any heavier and the bigest birds today could not fly. Gravity isn't really a force but a big hole which we find it hard to climb out of, ie with rocket power. I'm saying, that these very large and heavy( estimates of up to 300 pounds) animals would not be able to fly today. If they can't fly today and they could in the past then something has changed. :)

  • Comment number 51.

    #13 "Most girls dress to impress their friends and rivals firsts - guys're almost an afterthought.
    Homosexuality may even in part've evolved out of precisely this impress the competition routine."

    For some reason this point is usually deleted by the MODs on BBC websites (and i truly have no idea as its hardly offensive to homosexuals) but I'll make it again as Matt Walker seems to host a truly scientific site and might actually agree with me.

    The best suggestion for why we have homosexuality is that in a pack/tribe enviroment having a few healthy adults on hand to hunt/gather/babysit and who have no kids of their own gives a definite advantage to the kids the pack/tribe already has. Its been suggested that homosexuality is more common in 4th or 5th born kids than first born which might help support this theory.

    #46 Water seems the least of their problems. I've rarely seen an artists impression of a sauropod which doesn't have them grazing next to big lakes. Obviously these pictures are conjecture but to have enough foliage to eat would require plenty of moisture in their enviroment. Most of our dietary requirement for water is taken in as food (an orange is pretty much all water) so they'll be getting plenty from the leaves they ate.

    In any case water in is only half the story. Water out is the other side of it. Desert rats, Hamsters and to an extent cats have very long 'loops of Henle'
    http://en.wikipedia.org/wiki/Loop_of_Henle
    which mean they reabsorb almost all the water that filters through the kidney, excrete very concentrated urine and need to drink very little. Cats can only sweat through the pads of the paw so lose little moisture through sweating either. This is why they occaisonally survive 10 weeks in a shipping container from China. Overheating because they can't sweat is a bigger problem. God knows what the kidneys on a Sauropod were like but based on current wildlife I don't see a major problem with dehydration

  • Comment number 52.

    #50. You're not going to find many T-rex's on cliff faces either!

    Gravity is directly related to mass. For the gravity to be half what it is today requires the mass of the earth to be much less. Thats clearly not the case. The one thing that may have changed is the oxygen content in the air. I've seen several stupid figures like 70% oxygen (nonsense... things would keep spontaneously bursting into flame!) but even a few percent difference would allow much more vigorous muscle activity. (think of the difference in our performance between sea level & top of mount everest).

    My point about the hang glider was that you can do massive flights with a big wing with minimal energy exertion. You'd need a bit of a flap to get airborne and a bit of a flap to regain altitude but clever use of thermals and wind (which all big birds- condors, albatross can do) would manage it. One puny human even managed to human power himself across the channel (in a plane called the Gosamer albatross I believe). That weighed several hundred pounds and had a pretty dire power to weight ratio but still flew.

    Equally you have flying creatures (Pterosaurs etc aren't really dinosaurs) from about 200 million to 60 million years in the fossil record. Its rather like the guy who did the calculation and proved bumblebees can't fly... they clearly can and it was clearly a highly succesful design because it lasted that long

    This might be useful. Its proper peer reviewed science on how these big creatures did fly.
    http://scienceblogs.com/tetrapodzoology/2009/02/pterosaur_breathing_air_sacs.php

  • Comment number 53.

    Did it evolve? Did it even exist? If one considers the giraffe, as I understand it, the closed similar animal that we have today. It was designed and did not evolve. Consider this:- it stands 19' tall, weighs 2300 lbs, can run 35 mph, eats around 210 lbs of food in 16-20 hrs. Sleeps about 20 mins and can spend months without water. It has a large heart to send the blood up to its head. Now for the problems:-
    To drink water it has to lower its head and neck leading to at least 2 problems. Firstly once its head is down to enable drinking its now in danger of attack. To run or move quickly means a fast raising of its head. To raise its head quickly requires a very high blood pressure to get the blood up to the head - subjecting it to air embolism? A very dangerous high BP? leading to death.
    Under normal circumstances there is sponge like area round the head which absorbs the blood to allow the head to be lowered.
    These are just some of the difficulties. The main one is how does it pass this to his offspring.?

  • Comment number 54.

    @Charles Leedham-Green

    This is another cool aspect of evolution by natural selection!

    Because your fitness depends on your success at passing on genes down through subsequent generations (we are afterall 'gene-machines' according to Dawkins), ANY trait which allows your genes to be passed on more effectively will be selected for.

    Sometimes traits can be selected for which confer no advantage on the individuals lifespan etc. and they may therefore appear to be 'useless'. However, something that allows you to attract lots of females, will not only benefit you, but also your kids who will have that trait. Females who have a preference for that trait also benefit because her kids will gain that same advantage of being 'sexy'.

    This trait therefore doesn't have to have any obvious benefit to continuing the invividuals lifespan etc. but because it gives an advantage to its beholder, it becomes valuable. Potentially neutral or 'useless' traits may arise in this way, simply because of this bizzare benefit to mating with an individual with that trait.

    In-fact, if that trait is costly for a male, only the better males may be able to keep it up. For example bright feathers which attract predators will only be owned by males who are good at fighting off attack etc. Females will benefit from having a preference for that trait because by choosing a male with that trait, they choose a better quality male.

    Thus traits which have a neutral or even detrimental effect on an individuals chances of survival, may allow them to attract more mates and give their genes a transmission advantage.

    This is more or less the premise for sexual selection

  • Comment number 55.

    At 14:33 24th May 2011, Peter_Sym wrote:
    "My first degree was in genetics so I'm quite familiar with the idea of 'neutral traits' at least on one level. Blue or Brown eyes in the European population would be an example of something that persists because it doesn't really matter one way or the other. Blood groups would be another".

    I am a blood transfusion and organ transplantation scientist. Just wanted to point out that over 300 blood groups have now been discovered and evidence has shown many of these do serve a purpose. An example is people with blood group O are 'protected' from the worst form of malaria. The rosettes that form in people with malaria block small blood vessels and this reduces the supply of oxygen to the brain. It is 'harder' for the rosettes to form in people with blood group O. Other functions of various blood groups include transport channels, complement regulatory proteins and structural functions.

    Many of the comments posted may provide answers to the topic in question. In my opinion there is not a single reason as to the large size of the neck. A combination of sexual selection and reaching food has probably led to the evolution of the large neck. In addition, and @ Mike Taylor, is it possible that a long/strong neck was a symbol of leadership in a 'herd' of dinosaurs and that the dinosaur with the largest neck led the herd and that this dinosaur could better protect the other members of that herd and was the best dinosaur to find food and to find shelter as it would be able to see further. Perhaps the fact that a dinosaur was male or female made no difference in terms of which sex led the 'herd'. Just a thought....

  • Comment number 56.

    Mike Taylor, thank you so much for the link to your paper, I'm a zoology undergraduate at Royal Holloway but I couldn't access your paper through our system so it was very much appreciated.

    Having read your paper, you present a much stronger argument than Senter in my eyes. Senter's paper wasn't very convincing to me, I read it before I read your own so I had no bias toward yours before I began. I've struggled with the idea that giraffes necks were selected for by sexual selection, as you stated the proteins are more abundant at the upper leaves and toxic herbivore defences are in the lower leaves. I did question his assertion regarding allometry as Gould in 1973 demonstrated that Artiodactyla antler length was driven by nutrient availability rather than sexual selection I think, subsequent research showing in Megaloceros that antlers are reduced in size if phosphorus and calcium rich plants are scarce, I don't if this analogy is relevant or not. Is this applicable to the skeletal structures of elongated necks too?

  • Comment number 57.

    ~47 "For example, hip width in humans: Females do better with wider hips, but males 'prefer' narrower. Sexual dimorphism in hip width extinguishes the conflict."

    Er...do males "prefer" narrower in all cultures, over all times? Or just in Western cultures, now? What I have read of some African countries suggests the latter - big is better. This sort of assertion underlines the problem with all humans "sexual selection" theories - the tendency to ascribe current cultural preferences to all humans and pre-humans who existed thousands or millions of years ago.

  • Comment number 58.

    Am I the only one who gets frustrated by the poor understanding shown when phrases- such as 'the main driver'- that imply intent are used for something that was also 'caused by a chance mutation' implying no intent? I don't think the weeds in my lawn intentionally planned to only grow a few centimeters tall, rather only those that do survive the lawnmower.

  • Comment number 59.

    Necks are surely explainable. In the Jordanian desert, it is very noticeable that the few trees are cropped bare to the height of a stretching camel. But tails! What about those huge powerful tails? There would be better ways to make a weapon (e.g. club or spikes on the end like some other dinos). Could it have been a counterbalance for rearing up?

  • Comment number 60.

    This comment has been referred for further consideration. Explain.

  • Comment number 61.

    All this talk of size and gravity reminds me of a childhood fear.

    What if fossils expand as they get older? Tyrannosaurus Rex might only be a foot high. That really worried me when I was six. It still worries me a bit now.

  • Comment number 62.

    #53 - You need to grasp the immensity of evolutionary time. It would only be a problem if you had to "make" a giraffe for a 4 thousand year old planet. Lengthening a neck by a fraction of an inch per generation is no problem.

    #57 As Humans are in all probability the most complex social animals it would be surprising if our sexuality wasn't equally complex. Broad hips may equate to easy childbirth. Narrow hips signify youth and suggest a lack of sexual activity which in turn suggest longer reproductive potential and freedom from reproductive diseases.

    #58 Yes & no, our understanding is evolved too, we emulate the effects of evolution through design - it's hypothetical evolution if you like.

  • Comment number 63.

    Lots and lots to reply to ... I hope it's not rude for me to keep coming back and commenting on this. Anyway, let's take a few comments.

    #30 Dave wrote: "The giraffe, if I understand correctly, actually has to expend energy to lower the neck as the weight of the whole head/neck structure is counterbalanced by the massive ligament running up the back of the neck. I would have thought that such structures would define the 'neutral' position."

    Ah, we are on the vexed question of "neutral" neck position. What is neutral? Stevens and Parrish defined Osteological Neutral Pose (or ONP) as the posture in which the vertebrae of the neck best fit together, but that pose bears no relation to how animals habitually hold their heads and necks: in our 2009 we looked at salamanders, mammals, turtles, lizards, crocs and birds, and found that they ALL habitually hold their necks raised above the "neutral" pose, a habit that we have to assume was ubiquitous throughout Tetrapoda.

    In any case, the camel is apparently the only known animals in which the ligaments you mention, unaided by muscles, hold the neck as high as ONP -- which of cours is below habitual posture. So ALL animals (yes, including us) continually fire muscles in our neck to maintain posture. That's one reason we need to sleep.

    #32 Matt Walker BBC wrote: "Regarding the idea that traits have to be advantageous to persist: can you help me and maybe Peter_Sym and Paul J. Weighell out with some more insight? Can you explain a little about neutral traits or evolutionary drift (such as ideas that some traits can persist not because they are advantageous, but because they do no harm, or may even persist as they are somehow attached to another traits that are positive), and how these might not apply to a trait such as long necks that persists for such vast expanses of time?"

    I'm afraid that here I am outside my speciality, and all I can offer is this rather obvious observation: a feature with neutral adaptive value (i.e. neither helps nor hurts) can indeed persist; but a multi-tonne neck (I estimated that of Giraffatitan brancai at about three tonnes in a 2009 paper) doesn't fall into that category. Keeping all that tissue fed and oxygenated would be challenge enough; holding it off the ground requires enormous energy. These are not neutral structures: they must have been earning their keep, whether by feeding advantage of sexual selection.

  • Comment number 64.

    #33 Garry wrote: "[various stuff, then]... Thats the problem with all these non-technical story-like arguments. Biologists really need to take a hint from Physics."

    Garry, PLEASE read the paper before making comments like this. The "non-technical story-like arguments" are backed up by solid science.

    #44 Peter_Sym wrote: "The really big dinosaurs are the 'sexy' ones that look good in pictures but most species were no bigger than dogs (or perhaps Turkeys might be a better example....)."

    Actually, no. There are indeed plenty of known dinosaurs that were turkey-sized or dog-sized, and few that are chicken-sized or even pigeon-sized, but they are definitely in the minority. The median size for non-avian dinosaurs would be somewhere in the cow-to-rhino range, and elephant-sized or bigger dinosaurs were the dominant players in most Mesozoic ecosystems that we know of.

    "The largest animal ever known to have lived (Blue Whale ~200 tons) is alive today (just). Thats heavier than anything in the fossil record."

    Just! For a careful and interesting comparison of whale and sauropod sizes, see this post by my co-author Matt Wedel:
    http://svpow.wordpress.com/2008/05/20/sv-pow-showdown-sauropods-vs-whales/
    TL;DR: there's reasonably good evidence for sauropods topping 120 tonnes; other estimates have suggested as much as 220 tonnes, but that's not so well supported.

    "The big flying dinosaurs weren't really flappers but gliders. They were big but not especially heavy."

    Hmm, not so much. First of all, by "flying dinosaurs", I assume you mean pterosaurs. They weren't dinosaurs, though they were probably fairly closely related to them: the real flying dinosaurs are of course birds. Anyway, the evidence seems to be that biggest pterosaurs of all, the azhdarchids, really were flapping flyers and not soarers. They best mass estimates for these animals is about 250 kg, which is more than 20 times the mass of the heaviest modern flying animal. Astonishing but true. Read on ...

    Oh, and check out this astonishing artwork to get a gut-level feel for the size of big pterosaurs:
    http://scienceblogs.com/tetrapodzoology/2007/09/it_could_look_a_giraffe_in_the.php

  • Comment number 65.

    55. At 16:00 24th May 2011, Delia wrote: "is it possible that a long/strong neck was a symbol of leadership in a 'herd' of dinosaurs".

    Nice to theorise, but I wonder if there is any evidence that dinosaurs were herd animals? Or indeed any evidence at all about their social structure? I can't imagine that would be easy to come by...

    I also wonder this in the light of the postings about males thumping their necks against each other in stag-like dominance contests. Perhaps they were shy retiring creatures who did not seek the company of others, except once every few years when the need for mating came upon them. Perhaps they then just mated with the only other single giant dinosaur of the opposite sex for miles around - after all each one must have needed quite a bit of space, given how much they ate. Maybe that implies that if they were after all in herds, they must have been fairly nomadic, stripping one area fairly bare then moving on...Just speculating in a light-hearted fashion...:-)

  • Comment number 66.

    Interesting, I'd not heard about the Gould study. My guess is that it wouldn't apply directly to sauropod necks for two reasons: first, of course, I don't believe that sauropod necks were sexually selected anyway; and second, antlers are regrown every year, which makes them a particularly profligate waste of resources, whereas you only ever grow one neck.

  • Comment number 67.

    Maybe there weren't very many of them and they needed very low frequency calls in order to be able to communicate over long distances? Like elephants, only more so.

  • Comment number 68.

    I think Delia (comment 53) is probably right. Why not a combination of natural and sexual selection? Why do people always search for one single cause for a given event?
    It's like the debate about dinosaur extinction- big lump of rock from space or volcanic activity? Why does it have to be one or the other?

  • Comment number 69.

    i've enjoyed reading the article and all the replies and my offering has nothing to the point.

    Mark Taylor, many's the time i have been confounded while posting in too small a box, then finding that another has posted prior and nabbed my spot. i then compound the error by back-paging, thus losing my magnum magnificat (my latin). so irritated (incandescent with rage) did i become that i took to composing my erudite and witty reposts in a text editor first. this gave me the time luxury of also proofing it a bit (and always missing something that ends up making me look a prat). text editor - proof - post - simples.

  • Comment number 70.

    Surely it could be a bit of both? If a longer neck enabled offspring to reach a greater amount of vegetation for food, then wouldn't this also be a desirable trait for selecting a mate if the longer neck made the offspring more successful? It would therefor follow that the female would find this trait more sexually appealing and would also result in the minimal distance in neck length between males and females.

  • Comment number 71.

    I think this hypothesis is very thin and on a wrong tangent.

    Living things tend to BE what is needed to do, live, reproduce and further the species.
    Darwin's theory did not just begin in the Galapagos; it started with the first life forms.

    Assuming that the trees were very tall I doubt the foliage was similar to todays.

    However, if we take a look at the animal, imagine how well it would do in a lakeland scenario.
    It needs a large body to retain the heat, because it was probably cold blooded.
    A Long neck helps it breathe in deep water.
    The position of its nostrils are in perfect position for it to be in water for long periods.

    A long tail and neck enables it to balance and swim like a snake.

    A long neck helps the animal to reach down to the bottom of lakes where cogitation can thrive in the warmer climates of their age.

    A very well adapted animal for the environment I propose but a little necking was also prevalent because they were around for quite some time.

    So the Doc is correct but for the wrong reasons.

  • Comment number 72.

    Aborky-
    don't forget that in insects, spiders, fish, reptiles, non-avian dinosaurs and avian dinosaurs (birds), and even some mammals, the females are larger than the males. As for the sexual selection hypothesis, nature seems to have a way of making multiple uses out of any given feature. A long neck allows the sauropod to reach the top leaves, while simultaneously allowing it to see for great distances and thus spot danger, and also allowing males to demonstrate their health and genetic superiority over rivals during the mating season, and allowing females to select the best male.

  • Comment number 73.

    Oh dear, Kelly (#71), you are mistaken on so many levels. To pick just a few: Mesozoic foliage WAS similar to that of today's conifers (and, in the late Mesozoic, to that of modern deciduous trees, too); sauropods were almost certainly not cold-blooded; their fossils are found primarily in dry terrestrial environments rather than in lakeland environments; they were not aquatic animals; even if they had been aquatic they would have been unable to sink below water-level due to their low density caused by air-filled bones and an avian-style respiratory system; even if they had been able to sink below the surface of lakes, they would not have been able to breathe through long necks due to the pressure differential; the external nostrils of sauropods were at the front of the skull rather than on the top as naively implied by the positon of the bony nostril; most sauropods' necks and tails were very different in size so they would not have balanced particularly well; sauropods were not good swimmers, being unstably bouyant; "like a snake"?!; cogitation thrives in brains and nowhere else ... *gasp* *gasp*

    I don't like to harsh on you, Kelly, but really. If you're going to begin your comment with "I think this hypothesis is very thin and on a wrong tangent", you really need to make sure you have at least some background knowledge. A little humility goes a long way.

  • Comment number 74.

    SUrely it could be a bit of both, as in both sex and food. The longer neck allowed them to get more food, and so more likely to survive, and that makes them a more sexually viable candidate than the ones with a shorter neck, because they can more easily get food etc. You know natural selection and all..........

  • Comment number 75.

    And what's this I always read about a huge heart being needed if the head is held high? Nonsense. A domestic CH system needs no more pumping to send water high than to send water along. Pressure you lose on the way up you gain on the way down again. Very basic hydrodynamics, which holds even if the pipes are flexible. Of course the absolute pressure has to be high at the lower levels of the animal, but the pumping energy is not affected.

  • Comment number 76.

    63. At 17:01 24th May 2011, Mike Taylor wrote:
    "Lots and lots to reply to ... I hope it's not rude for me to keep coming back and commenting on this."

    No. it's great that you do.

    Re big necks; "These are not neutral structures: they must have been earning their keep, whether by feeding advantage of (sic) sexual selection."

    The other factor, as someone else pointed out, is related to time - these necks had to evolve over time. Why? I assume that habitat change can be a big spur to evolution - and, as I implied in an earlier post, some fairly serious habitat change must have driven some human evolution. (Sidetrack - post 71 gives me the chance here to mention - oh no! - the aquatic ape theory of human evolution).

    Obviously habitat change spurs evolutionary pressure re feeding advantage - I wonder if it is simply a "subcategory" of feeding advantage, though, or whether it deserves to be listed as a third category of "evolutionary driver".

    In this context, then, the surroundings in which we picture our earlier dinosaurs, that will eventually evolve long necks, may be very different from the surroundings that they ultimately find themselves in. I know this seems obvious...but it doe snot seem that all the post above have this in mind.

  • Comment number 77.

    Re my comment 76 - sorry about typos in last line! I should make it clear that I have no idea at all if the habitat of these long-necked dinosaurs actually did change significantly over the time that they evolved. Just wondered if anyone else did?

  • Comment number 78.

    #63 on #32. Neutral adaptive value ought to be considered in the context of competitive evolution. If you've evolved a big neck that you no longer need it's part of your genetic blueprint that must compete with other individuals in its entirety. It's hard to see how it would be a disadvantage in your ability to carry out your day to day activities, only in the efficiency of them. It would be easier for species to specialise than it would be to return to a more generalised strategy. Mass extinctions are evidently more common than regressive evolution.

  • Comment number 79.

    A redundant chunky neck would serve nicely as a sexual indicator of general fitness the same as fancy plumage that is a specialised adaption for mating display. Perhaps that's how display adornments got started?

  • Comment number 80.

    I am grateful to the responses to my comment on sexual attraction. The responses
    accuse the sexual preference gene of being illogical. It is an error, from a
    game-theoretic point of view, to prefer a potential mate with a disadvantageous feature on the assumption that they must have a compensating advantage. A one-legged soccer player must be skilled at heading the ball, but ...

  • Comment number 81.

    As I understand the idea, sexual selection would mean that offspring produced by females selecting makes with longer necks would possess the genes for the longer necks and also genes for the preference itself. Hence the "runaway" effect. But I don't entirely understand why sexual dimorphism should automatically follow unless those genes just happened to be present on the sex chromosomes (as in the case of peacocks).

    Isn't the evolutionarily rapid increase of brain size in Homo sapiens also a possible example of sexual selection in action?

    By the way, I cannot see any possible mechanism by which genes for homosexual preferences could be propagated by children benefiting from this in some sort of group selection manner, as suggested above. If I'm missing something here, please elaborate.

  • Comment number 82.

    As far as I can see the genetic mutation favouring long necks, larger sizes etc would have been advantageous mostly for feeding but also in the arms race against predation. I see the benefit of the arms race against the growing flora too. I would have thought that the sexual selection and these advantageous mutations would go hand in hand, so that both ae true. The long necks and massive size certainly weren't used for fighting or prehistoric hide and seek. Elevated vision would have been a boon for a nomadic herd species. It's most likely given the nature of large plant eaters that sauropods travelled in herds. I know that we can't look directly into the past but looking at modern equivalents I'd say that small herds would fit the mould. As was pointed out earlier, desirable traits are generally for sex, food or fight. Size for fight, long neck for food and both for sex.

  • Comment number 83.

    So far, mburland has made the only sensible comment. Evolution is a hoax and is slowly being proved to be so. It is a false religion built on supposition and guesstimates. The evidence rather more supports the creation argument.

  • Comment number 84.

    @83, Quartus45: Evolution is science not religion. It is built on scientific evidence, it is most definitely not built on guess work. According to mburland it is 'logical and reasonable' to assume they were just 'created'.....from what? fairy dust????!

  • Comment number 85.

    Thank you for the reply Mike, i was just wondering as the structure of antlers and bone is similar. It's a study i came across while writing my project on Megaloceros phylogeny so I wondered if the principal was the same. On reflection nutrients would facilitate rather than be a driving force I guess. Clearly the diet was able to sustain the large body size and development of the elongated neck. I'm also curious about how your own and Phil Senter showed the lack and presence of sexual dimorphism, was there a bias in the methodology that caused that?

  • Comment number 86.

    your own study that should read on the 5th line, apologies about that.

  • Comment number 87.

    Wow. Rule 1 of the internet is "Don't read the comments" but this page is a definite exception. Thanks to almost everyone for keeping up a really high standard of thoughtful comments and especially to Mike Taylor for spending so much time explaining his work. Perhaps the BBC could arrange to have this sort of thing happen more often? I'm sure you could make a feature of having a journalistic summary of an interesting paper or concept, such as this one, and then invite one of the paper's authors to contribute to the comments page.

    But, please, everyone. Let's not get side-tracked onto the evolution-vs-creation debate. The chance of anyone convincing anyone on the other side of that debate to change their mind is essentially zero.

  • Comment number 88.

    Okay, Delia, where is your scientific evidence for any of the theories put forward? The fossil record does not support any of them. Indeed, the fossil record confirms that life forms reproduce "after their kind" and many life forms are immediately recognisable for what they were because they are still alive today (your religion calls them "living fossils"). There are no "transitional" fossils.

    I repeat - evolution is a religion. It is a blind faith built on supposition and guesstimates.

  • Comment number 89.

    David Richerby is spot on when he says "The chance of anyone convincing anyone on the other side of that debate to change their mind is essentially zero." The evolutionist is so thoroughly brainwashed that he ridicules any contrary statement to his religion. It is just so sad that that they refuse to consider any differing view and insist on stating their case as though it were hard, established fact. We've all suffered the same brainwashing, but some of us have looked at the evidence with an open mind and found that the argument for evolution does not hold water.

  • Comment number 90.

    #75 Billthegeek wrote: "And what's this I always read about a huge heart being needed if the head is held high? Nonsense. A domestic CH system needs no more pumping to send water high than to send water along. Pressure you lose on the way up you gain on the way down again. Very basic hydrodynamics, which holds even if the pipes are flexible."

    Sadly, no. This idea was tested by haemodynamics specialist Roger Seymour back in 1993 and found wanting. The reference is:

    Seymour, Roger S., Alan R. Hargens and Timothy J. Pedley. 1993. The heart works against gravity. American Journal of Physiology 265: R715-R720.

    And the abstract is as follows:

    The circulatory systems of vertebrate animals are closed, and blood leaves and returns to the heart at the same level. It is often concluded, therefore, that the heart works only against the viscous resistance of the system, not against gravity, even in vascular loops above the heart in which the siphon principle operates. However, we argue that the siphon principle does not assist blood flow in superior vascular loops if any of the descending vasculature is collapsible. If central arterial blood pressure is insufficient to support a blood column between the heart and the head, blood flow ceases because of vascular collapse. Furthermore, the siphon principle does not assist the heart even when a continuous stream of blood is flowing in a superior loop. The potential energy gained by blood as it is pumped to the head is lost to friction in partially collapsed descending vessels and thus is not regained. Application of the Poiseuille equation to flow in collapsible vessels is limited; resistance depends on flow rate in partially collapsed vessels with no transmural pressure difference, but flow rate is independent of resistance. Thus the pressure developed by the heart to establish a given flow rate is independent of the resistance occurring in the partially collapsed vessels. The pressure depends only on the height of the blood column and the resistance in the noncollapsed parts of the system. Simple laboratory models, involving water flow in collapsible tubing, dispel the idea that the siphon principle facilitates blood flow and suggest that previously published results may have been affected by experimental artifact.

  • Comment number 91.

    @Quartus45: David Richerby was also correct to say 'Let's not get side-tracked onto the evolution-vs-creation debate'.

    I also do not think you are correct in saying people who agree with evolution principles have been 'brainwashed'. Has it not occurred to you that out of 90 comments posted on here only one other person agrees with what you're saying? All the other 88 people who have commented must incorrect and you must be right!

    I am actually a very open-minded person and I have no problem whatsoever with other peoples beliefs, but to say evolutionary scientists are brainwashed is a step too far and is way off the topic under discussion. You asked me for scientific evidence for the theories put forward, let me ask you for scientific evidence that sauropods were just 'created'. If you provide that, then I will consider your claim.

  • Comment number 92.

    Charles L-G (80): "It is an error, from a game-theoretic point of view, to prefer a potential mate with a disadvantageous feature on the assumption that they must have a compensating advantage."

    Interesting point. Actually, the costs and benefiits of the two traits can balance out. This is known as the "handicap hypothesis", the idea being that, for example, a peacock with an especially fine tail is signalling to the females that his other genes, e.g. for disease resistance, are so strong that he can survive despite being encumbered by his tail. As disease resistance is important almost all the time, a gene that causes him to signal that he is likely to produce healthy offspring can be favoured by natural selection.

    It's also known as the Moshe Dayan effect. It was first proposed by an Israeli biologist called Daniel Zahav and the story goes that when he first described it at a conference, someone stood up and said, "that's ridiculous! It's like saying the best soldier will have only one eye." At which Zahavi shrugged and said, "one of our best generals has only one eye."

  • Comment number 93.

    "David Richerby is spot on when he says "The chance of anyone convincing anyone on the other side of that debate to change their mind is essentially zero." The evolutionist is so thoroughly brainwashed that he ridicules any contrary statement to his religion. It is just so sad that that they refuse to consider any differing view and insist on stating their case as though it were hard, established fact. We've all suffered the same brainwashing, but some of us have looked at the evidence with an open mind and found that the argument for evolution does not hold water."

    Google "Walter Veith" - he used to be a top evolutionist and then became a Creationist. I am not going to judge one way or another about people's motives who claim evolution as fact - that is for God to decide for the Day of Judgement - Jesus Christ is the truth and so is Creation - have the courage to oppose the "Goliath" of evolution.

  • Comment number 94.

    #87 David Richerby wrote: "Wow. Rule 1 of the internet is "Don't read the comments" but this page is a definite exception. Thanks to almost everyone for keeping up a really high standard of thoughtful comments and especially to Mike Taylor for spending so much time explaining his work. Perhaps the BBC could arrange to have this sort of thing happen more often? I'm sure you could make a feature of having a journalistic summary of an interesting paper or concept, such as this one, and then invite one of the paper's authors to contribute to the comments page."

    This sounds like a great idea to me. I'd be more than happy to participate in this way.

    "But, please, everyone. Let's not get side-tracked onto the evolution-vs-creation debate."

    Indeed. Rule 2 is of course Don't Feed The Trolls.

  • Comment number 95.

    OK, sorry, I know I said I wouldn't get dragged into this, but as a point of information I have to say that Walter Veith absolutely was not a "top evolutionist" -- I've never even heard of him, and it's my specialist field. His own page at http://amazingdiscoveries.org/speakers-WalterVeith1.html says that his research field is nutritional physiology, which is not particularly relevant. I've not been able to find a list of his peer-reviewed publications anywhere; but it was easy to find a list of his "products". Draw your own conclusions.

    *sigh*

  • Comment number 96.

    @Mike Taylor, #94: You are, of course, correct.

    I wonder if you would be kind enough to tell me your thoughts on my question/thoughts in the last paragraph of comment 55?

  • Comment number 97.

    "OK, sorry, I know I said I wouldn't get dragged into this, but as a point of information I have to say that Walter Veith absolutely was not a "top evolutionist" -- I've never even heard of him, and it's my specialist field. His own page at http://amazingdiscoveries.org/speakers-WalterVeith1.html says that his research field is nutritional physiology, which is not particularly relevant. I've not been able to find a list of his peer-reviewed publications anywhere; but it was easy to find a list of his "products". Draw your own conclusions.

    *sigh*"

    Maybe he was working at a university in the field before your time.

    If you watch his video testimonial about his evolutionary work and change of opinion with an open mind, it might just change your life: "http://amazingdiscoveries.org/media-Walter-Veith-testimony.html" - and he has made other videos also about evolution: "http://amazingdiscoveries.tv/c/9/Science/" - personally I like these numerous anti-evolution articles (by another organisation): "http://www.icr.org/index.php?module=articles&action=search&f_typeID=9" - oh yes and all these videos/articles are free to view/read.

  • Comment number 98.

    #97 www_onlinechristianityteacher_com, in the sciences a person's work isn't forgotten the moment they go off and do something else, or indeed when they die. I spend a huge proportion of my own time in the literature reading works by the likes of Marsh and Cope (19th Century) and Janensch and Osborn (early 20th). If Veith had been a "top evolutionist" at any point, I would have seen or at least heard of his papers. Sorry but that's the truth.

    #96 Delia asked me specially to address her own earlier question from #55: "Is it possible that a long/strong neck was a symbol of leadership in a 'herd' of dinosaurs and that the dinosaur with the largest neck led the herd and that this dinosaur could better protect the other members of that herd and was the best dinosaur to find food and to find shelter as it would be able to see further."

    I think that is perfectly reasonable to imagine -- after all, elephant herds are usually led by the largest individual -- but I can't think of any way to test the idea. Behaviour is notoriously reluctant to fossilise :-)

    "Perhaps the fact that a dinosaur was male or female made no difference in terms of which sex led the 'herd'. Just a thought...."

    i think that's unlikely, just based on analogues of animals that are alive today. I can't offhand think of any species where a herd might be led at random by either a male or a female. (Well, with the possible exception of Homo sapiens!)

    By the way, this touches on paulbyork's question in #65, "I wonder if there is any evidence that dinosaurs were herd animals? Or indeed any evidence at all about their social structure? I can't imagine that would be easy to come by..."

    For some dinosaurs, especially for some reason centrosaurine ceratopsids (dinosaurs kind of like Triceratops) there are several mass death assemblages which are hard to interpret as anything other than a herd getting caught in a flood. For sauropods it's not quite so clear cut, but there certainly are quarries that contain several individuals that died together (and often individuals of multiple species).

    But remember that Sauropoda was a huge and very long-lived group, and behaviour would certainly have varied between species, just as today tigers are solitary but lions live in prides. Based on patterns of fossilisation it's not unreasonable to guess (but it's only a guess) that Brachiosaurus was solitary but Camarasaurus was gregarious.

  • Comment number 99.

    "#97 www_onlinechristianityteacher_com, in the sciences a person's work isn't forgotten the moment they go off and do something else, or indeed when they die. I spend a huge proportion of my own time in the literature reading works by the likes of Marsh and Cope (19th Century) and Janensch and Osborn (early 20th). If Veith had been a "top evolutionist" at any point, I would have seen or at least heard of his papers. Sorry but that's the truth."

    Check out at 1 hour and 3 minutes: "http://amazingdiscoveries.org/media-Walter-Veith-testimony.html" to give an indication what he was up against.

  • Comment number 100.

    @Mike Taylor: thanks for your response.

 

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