Repeated evolution: Penis-baculum evolved multiple times and have been lost multiple times

Several hypotheses for the function of the baculum have been proposed which lead to testable predictions in a comparative framework. Unfortunately, comparative studies have failed to yield general and consistent results 

Here, we specifically test this hypothesis by modeling the presence/absence of bacula of 954 mammalian species across a well-established phylogeny and show that the baculum evolved a minimum of nine times, and was lost a minimum of ten times