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29 October 2014

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Does Size Matter?


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In the animal world, the battle of the sexes doesn't end with finding and courting a mate. For the males, the act of mating can be a difficult and dangerous business.

And in many species, evolution can favour females who are able to select only the fittest sperm from the fittest males.

From fruit flies to elephants, take a look at the weird and wonderful world of animal reproduction.

Fruit flies

Fruit flies

The tiny fruit fly Drosophila bifurca produces sperm that is 10mm long. Do you think this statement is correct?

That statement was wrong. The tiny fruit fly Drosophila bifurca produces sperm that is almost 6cm long, more than 20 times the size of its body. Female fruit flies may have evolved longer reproductive tracts alongside a preference for longer sperm. The males that can produce the longest sperm, those that can travel all the way to the egg lying at the end, will automatically be selected to father offspring.

Snakes

Snakes

Some snakes have two penises. Do you think this statement is correct?

That statement was correct. Some snakes do have two penises. The reason for the split arrangement isn't clear. But many snakes indulge in group matings where hundreds of them compete for females. It may be that the twin organs allow them to copulate more frequently - one side can recover while the other is still in use.

Hyenas

Hyenas

Female hyenas have such an extended clitoris that they look exactly the same as a male with a penis. Do you think this statement is correct?

That statement was correct. Female hyenas have such an extended clitoris that they look exactly the same as a male with a penis. Because of this extended clitoris it's very difficult for the male to mate effectively. It may be that the female uses her long and convoluted reproductive tract as a barrier to screen out the males who aren't up to the task.

Chimpanzees

Chimpanzees

Chimpanzees only mate to make babies. Do you think this statement is correct?

That statement was wrong. Pygmy chimpanzees, or bonobos, appear to be the only primates other than humans that indulge in sex for reasons other than reproduction. Sex in bonobos is used not just to make babies - resolving social conflicts as well as forming and reinforcing alliances seem to be equally important reasons for an intimate liaison in the trees.

Gorillas

Gorillas

An adult gorilla's erect penis is about 40cm (15in) in length. Do you think this statement is correct?

That statement was wrong. An adult gorilla's erect penis is about 4cm (1.5in) in length. Scientists speculate that the size of penises among primates may reflect the degree to which males have to compete with other males over partners. In gorillas, males may mate with many partners, but each female is monogamous, mating with only one male. As there is no competition between males, their penis size is relatively small.

Elephants

Elephants

The sperm of an elephant is shorter than the sperm of a mouse. Do you think this statement is correct?

That statement was correct. The sperm of an elephant is shorter than the sperm of a mouse. The incredible variety of sperm shapes and sizes found in the animal kingdom seem to be more closely linked to the level of promiscuity or the length of the female reproductive tract than anything else.




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