Location, Location, Location: A Real Estate Axiom For The Genesis Of Genitalia

Nature enjoys variety, that is why it seems like evolution must have been drinking during the creation of some of the crazier things in biology.  There is no intelligent reason why snakes and lizards have two genitalia while birds and people have one - or why the former group's paired structures are located somewhat at the level of the limbs while with humans and birds it appears a bit further down. In fact, snake and lizard genitalia are derived from tissue that gives rise to hind legs, while mammalian genitalia are derived from the tail bud. But despite such noteworthy contrasts, these structures are functionally analogous and express similar genes.  How do these equivalent structures arise from different starting tissues?  read more

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