Whales' Pelvic Bones: Evolutionary Science at its Best

This summer I took my kids to the Royal Museum for Natural Sciences here in Brussels. Apart from the usual dinosaur exhibits and a very nice exposition on evolution, there was also a large room (evidently) for the display of whale skeletons. Impressed by the sheer size, I added an educational note to the experience by pointing to the remains of the hip or pelvic bone. Explaining that whales were actually land mammals that returned to the sea, I told my kids this small bone was just what remained of the hip, where the now-lost legs attached. The correct word for it is "vestigial," and some researchers have even speculated that, given a few million years, this bone will probably disappear altogether.

But science keeps on evolving and getting better, so I probably need to give my kids a new tour of the museum with updated information. Futurity reported on an interesting study on whales, showing that the pelvic bonesare indeed necessary for sexual reproduction (for males). The penis is attached viamuscles to this bone,and so it cannot actually disappear.

What is even more interesting is that this bone is not "just there," but also undergoes evolutionary pressure. For instance, in whale species that are more promiscuous, the pelvic bone is bigger to allow for a more "mobile" penis and bigger testes (relative to overall body size). Monogamous whale species, on the contrary, have a very small pelvic bone, as there is no need to develop a larger apparatus. The researchers, who catalogued and 3D-scanned hundreds of skeletons, also showed that there is no correlation with rib size, so it is not just an issue of anatomic proportionsbut the result of a specific sexual selection strategy.

The Futurity article made a very good summary of the scientific paperby Dines et al. (to which they alwayslinkâ€"cool!), andis a very interesting read in and of itself. The researchers apply some reallyneatstatistical methods (including a Bayesian analysis). This is evolutionary science at its best.

And that is maybe what I will explain my kids, too. Not only the new explanation, but also why and how science got to that new explanation. I hope that as a result they will love evolution as much as I do.