Evolution: What the world's youngest species can teach us
When it comes to evolution, the world's youngest species can teach us more than the oldest.
When we think of evolution, we think old.
It's as natural as evolution itself. We think old, because it acts across vast time scales, and we see its hand down the ages, epochs and eras. Our focus on evolution as a grand old thing might partly explain our enduring fascination with extinct ancient beasts such as the dinosaurs.
Sometimes hybridisation reaches a different, natural end point: the emergence of wholly new, third species”
But when we think of evolution, we should also be thinking young.
Because some of the best evidence that evolution is happening, and how it happens comes not from the fossilised remains of the long fallen. It comes from still-living animals and plants; snails, fish, flies and flowers, for example.
And it comes from finding and studying the youngest species on earth.
Old species have their place. We love our fossils, and we particularly love our living fossils, a term we use to describe still-living species that have weathered, relatively unscathed, millions of years. They have proved themselves, in evolutionary terms, the great survivors: the fittest of the fit.
Rediscovered in 1938, coelacanths use their fleshly lobed fins to paddle the deep sea caves of the Indian Ocean. These modern coelacanths aren't much different than their long-dead relatives, another species of which was discovered in October this year.
EARLY LIFE ON EARTH
Crocodiles with their ancient, almost battered-looking bodies, have hardly changed in 230 million years; nautiluses for almost 500 million years. We celebrate when new living fossils are discovered, such as the aptly named Jurassic shrimp.
These species have evolved, of course, over the past millions of years, however subtly.
But their relatively unchanged nature serves to remind us, perversely, that other species can change quite a bit.
They either die out or evolve into something new and better able to survive; dinosaurs became birds, for example. Evidence of these transitions in the fossil record is some of the best evidence for evolution itself.Driven apart
But the old are giving way to the young.
Scientists are increasingly finding evidence of evolution in action. They are recording in numerous and varied detail how populations of similar animals, from lamprey and sea urchins to Drosophila flies and crickets, are diverging - splitting into two or more distinct groups, driven apart by natural processes.
WHAT IS A SPECIES?
What a species is, is itself not clear-cut. Biologists attempt to define and identify what a species is according to different criteria and concepts:
- Biological species concept: Individuals are considered part of the same species if they breed with one another and create viable offspring that themselves can breed. But that doesn't help explain species that reproduce asexually, such as bacteria, some insects and even certain vertebrates
- Phenetic species concept: Individuals are considered part of the same species if they look the same. But in many species individuals look quite different, such as soldier ants and worker ants
- Recognition species concept: A species is a set of organisms that can recognise each other as potential mates even if they are prevented from breeding, by a geographical barrier, for example
- Ecological species concept: A species comprises individuals that occupy exact the same ecological niche, regardless of their genes or to what extent genes flow between them
Some are driven apart by geography; it's how most species endemic to islands are thought to have appeared. Some are separated by morphology; a study published this month shows how populations of periwinkles are evolving elaborate and different penises, which prevents them mating with other populations of snail, isolating them into different species.
Some by their environment; scientists isolate different populations of Drosophila flies under unique laboratory conditions, and are able to experiment with evolution, testing how environments trigger new adaptations. Drosophila flies bred this way over hundreds of generations can diversify to become less thirsty, more aggressive or live longer, to name just a few.
Some are diverging because of their behaviour; two subspecies of the sea urchin Heliocidaris erythrogramma now spawn at different times in the seas off Western Australia, one in summer, the other in winter, scientists report in the journal Evolution. As a result, they are unable to mate, destined to take their own, separate evolutionary journeys, perhaps to become separate species.
Tangible, quantifiable, observable evolution.
Other species are doing the opposite. They are not being driven apart, but together.
Relatively recently scientists have discovered that hybridisation can be the origin of many species.
Many species hybridise; blue and pygmy blue whales have been discovered hybridising in the Southern Ocean, scientists report. Different species of red oaks trees reproduce with each other in the forests of North America. Similar species of lamprey, seagull, wasp and sunflower all regularly mate, producing viable offspring.
These species often hybridise in response to some environmental pressure; whaling or human-induced climate change is thought to be driving the two types of blue whale together.
Usually hybrids are infertile, as a horse and a donkey might produce a sterile mule.
But sometimes this hybridisation reaches a different, natural end point: the emergence of wholly new, third species.
It can be difficult to pinpoint just when this happens. But in June, scientists managed to do just that; publishing details of a small, inconspicuous species of monkey flower growing in the UK.
Their study published in PhytoKeys showed that this species, Mimulus peregrinus, is one of the youngest recorded, appearing less than 140 years ago. A new life form, emerging out of the bank of a stream in Scotland, within a few generations of our lifetime, perhaps even within that of Charles Darwin himself, one of the fathers of evolutionary theory.
Other species of plant break even that record.
In the 1880s a flower called Spartina anglica originated in Southampton Water in the UK.
In the mid-1900s another new flower, Senecio cambrensis, naturally speciated in North Wales in the UK, while around the same time two species of flower Tragopogon mirus and T. miscellus appeared in Washington State in the US.
These flowers were created by a process of hybridisation, where the genetic material of their parent plants fuses. The offspring have double or triple the number of chromosomes of their parents, with their DNA being arranged in such a way that fertility is restored.
Two other flower species have appeared within the lifetime of many of us.
PRIVATE LIFE OF PLANTS
More recently, in the latter part of the 20th Century, the flower species Cardamine schulzii appeared in Switzerland. Senecio eboracensis may have evolved into a new species even later, in the past 40 to 50 years, being discovered in 1979 in York, England, growing next to a parking lot and being formally described in 2003.
S. eboracensis is thought to have evolved from its parents, S. vulgaris, which is native to Britain, and S. squalidus introduced from Sicily in the early 18th century. The new species is already unable to reproduce with either of its parent plants.
These seven flowers may represent something much bigger, suggesting that new species are being created relatively often in nature, says a study published this month in the journal Molecular Ecology.
Reliably demonstrating their recent origin requires documentary evidence, which can be very hard to come by. But scientists can take the seeds from such flowers and cross them, attempting to reproduce the moment of speciation.
Such studies teach us much about the origin of species and about how evolution itself can work.
Evolution, and speciation, as we live.
Species so young we have the capacity to witness their birth.
Now that is something to think about.