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__Female ducks fight back against 'raping' males__
16:35 01 May 2007 NewScientist.com news service Andy Coghlan Some female ducks and geese have evolved complex genitalia to thwart unwelcome mating attempts, according to a new study. Males of some species, such as mallard, have a notorious habit of "raping" females. They and other wildfowl are among the 3% of bird species whose males have phalluses big enough to insert into the vaginas of females, whether or not the female consents. Now, in the most detailed analysis yet of duck and goose vaginas, researchers have established that females of these species have evolved vaginal features to thwart unwelcome males. Tim Birkhead at the University of Sheffield in the UK and colleagues examined vaginas and the corresponding phalluses from 16 wildfowl species. They discovered that the longer and more elaborate the male member, the longer and more elaborate its female recipient was. Some vaginas had spiral channels that would impede sex by twisting in the opposite direction to that of the male phallus. Others had as many as eight cul-de-sac pouches en route, that could prevent fertilisation by capturing unwelcome sperm. Moreover, these features were only found in species renowned for forced sex. All other species had simple male and female genitalia. “These structures are wonderfully devious, sending sperm down the wrong road or impeding penetration,” says Birkhead. He says that the features demonstrate an evolutionary "arms race" in which control over reproduction alternates between the sexes. If the male develops a longer, more elaborate phallus to force copulation, females wrest back control by developing features to thwart males who rape. “It shows that females are not passive in averting exploitation by males with large phalluses,” says Birkhead. The study appears in the online version of the journal
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__Chimps 'more evolved' than humans__
22:00 16 April 2007 From New Scientist Print Edition. Bob Holmes It is time to stop thinking we are the pinnacle of evolutionary success – chimpanzees are the more highly evolved species, according to new research. Evolutionary geneticist Jianzhi Zhang and colleagues at the University of Michigan in Ann Arbor, US, compared DNA sequences for 13,888 genes shared by human, chimp and rhesus macaques. For each DNA letter at which the human or chimp genes differ from our shared ancestral form – inferred from the corresponding gene in macaques – researchers noted whether the change led to an altered protein. Genes that have been transformed by natural selection show an unusually high proportion of mutations leading to altered proteins. Zhang's team found that 233 chimp genes, compared with only 154 human ones, have been changed by selection since chimps and humans split from their common ancestor about 6 million years ago. This contradicts what most evolutionary biologists had assumed. "We tend to see the differences between us and our common ancestor more easily than the differences between chimps and the common ancestor," observes Zhang. The result makes sense, he says, because until relatively recently the human population has been smaller than that of chimps, leaving us more vulnerable to random fluctuations in gene frequencies. This prevents natural selection from having as strong an effect overall. Now that the [|macaque genome has been sequenced], biologists will be able to learn more about the differences between the apes. Journal reference: //Proceedings of the National Academy of Sciences// (DOI: 10.1073/pnas.0701705104)
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