How the human penis lost its spines

You've read the headline, and it probably made you giggle. Go ahead. Get it out of your system. Then take a deep breath and consider how evolution affected a few specific body parts, and why.

Humans and chimpanzees share more than 97% of DNA, but there are some fairly obvious differences in appearance, behavior and intellect. Now, scientists are learning more than ever about what makes us uniquely human.

We know that humans have larger brains and, within the brain, a larger angular gyrus, a region associated with abstract concepts. Also, male chimpanzees have smaller penises than humans, and their penises have spines. Not like porcupine needles or anything, but small pointy projections on the surface that basically make the organ bumpy.

Gill Bejerano, a biologist at Stanford University School of Medicine, and colleagues wanted to further investigate why humans and chimpanzees have such differences. They analyzed the genomes of humans and closely related primates and discovered more than 500 regulatory regions -- sequences in the genome responsible for controlling genes -- that chimpanzees and other mammals have, but humans do not. In other words, they are making a list of DNA that has been lost from the human genome during millions of years of evolution. Results from their study are published in the journal Nature.

Think of it like light bulbs and their switches, where the light bulbs are genes and the switches are these controlling DNA sequences. If there's no bulb, the switch can't turn the light on. Now imagine there's one bulb and five switches to turn it on at different times in different places. If you take one of the switches ........


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Ducks fight the battle of the sexes in their genitals

If ever there was a story that illustrated the lengths a male will go to have sex, it is this. Male Muscovy ducks have a penis up to 40 centimetres long – almost half the length of their body – but that's just one of the twists and turns in the story of how female and male ducks try to outsmart each other.


A female Muscovy duck chooses a mate based on her assessment of his courtship and plumage. But rejected males don't give up easily, and can force copulation on unwilling females. The long, flexible penis helps them do so.



So females have evolved to wrest back control of copulation, says Patricia Brennan at Yale University. "The males and females become locked in this arms race, each trying to dominate the outcome. It's fascinating to find such a clear and obvious example of sexual conflict."



Do the twist

The male duck's penis is spiral-shaped: like a corkscrew, it twists in a counter-clockwise direction so that sperm will target the oviduct on the female's left-hand side. In almost all birds only the left ovary is functional, but in a 2007 study, Brennan and colleagues noticed that in ducks the female's vagina twists in the opposite direction.



To see whether these clockwise twists and turns would make copulation more difficult for the male, the group managed to get male ducks to unfurl their penises into glass tubes shaped like a female's vagina. The males found it difficult to evert their penises down the length of the tube – which is what the team reckons happens in the vagina.



Brennan thinks that, while the males are .........

WARNING - DUCK PENIS VIDEO





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