The penis only evolved once, suggests study of lizard embryos

The adult tuatara lizard (Sphenodon punctatus, seen above) has no penis. But among amniotic animals—reptiles, birds, and mammals—that’s not even that weird. www.glorybios.com Many snakes have double “hemipenes” and ducks have spiraling phalluses that look like fusilli pasta. This diversity in amniotic genitals has puzzled scientists as they try to map out the evolutionary tree of life. The fact that the tuataras don’t have penises makes them a useful study organism because it allows scientists to ask whether the lizards’ ancestors had penises and lost them, or never had them to begin with. Now, according to new research published today in Biology Letters, the last common ancestor of all the www.glorybios.com amniotes did, in fact, have an erectable phallus, and that the modern diversity is the result of evolutionary tweaks over time (not the separate evolution of different phalluses). The findings come from an analysis of Victorian-era tuatara embryos preserved on slides at the Harvard Embryological Collection. Scientists used pictures of the lizard embryos to recreate their 3D structure using computer software. The team discovered that, even though the tuatara has no external phallus, it grows the beginnings of one during development. At some point down the line this “genital swelling” recedes and the lizards are born sans phallus. The embryonic development suggests that amniotic penises only evolved once, but that some animals have lost theirs over time. www.glorybios.com