An interesting new investigation has revealed a molecular mechanism on how human males evolved into having smooth penises, rather than penises studded with small, hard spines such as those in our closes cousins, the chimps {link open for free only for a limited time}.
They first systematically identified 510 DNA sequences missing in humans and present in chimps, finding that those sequences were almost exclusively from the non-coding regions of the genome, between genes. They then homed in on two sequences whose absence in humans they thought might be interesting — one from near the androgen receptor (AR) gene and one from near a gene involved in tumour suppression (GADD45G).
Inserting the chimpanzee sequences into mouse embryos revealed that the former sequence produced both the hard penile spines and sensory whiskers present in some animals. The latter sequence acted as a kind of brake on the growth of specific brain regions — with the removal of its function appearing to have paved the way for the evolution of the larger human brain.
This study is published in Nature (McLean, C. Y. et al. Nature 471, 216-219 (2011)).
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