Elvis Presley earned the moniker of “Elvis the Pelvis” for his tendency to gyrate his hips in erotic fashion. It turns out that whales and dolphins, known as cetaceans, also use their pelvic bones in the most sexual of ways.
Forty million years ago, whales’ and dolphins’ ancestors walked the Earth and a pelvis was crucial for that task. Today, cetaceans, of course, are ocean dwellers, but their anatomy still includes pelvic bones. Marine biologists had thought that the pelvic bones were purposeless in the marine environment, and would eventually disappear given another million or so years of evolution. But now, a comparative look at different species’ pelvic bones reveals that they may have an unsung benefit: helping maneuver cetaceans’ penises.
Gettin’ Busy Bones
The muscles that control the highly mobile penises of whales and dolphins attach directly to the pelvis, so researchers wanted to see if pelvic bone size and genitalia size were correlated.
Since cetaceans are in highly competitive mating environments (females mate with numerous males), having the biggest and most agile member might give the male an advantage over his competitors, researchers reasoned. That would lead to larger pelvises being evolved through sexual selection, since a bigger pelvis would allow for a more flexible organ.
How They Measured Up
Using precise 3-D scanning and measuring techniques, scientists examined 130 pelvic bones from 29 different cetacean species. Then, they gathered data – as far back as whaling days – on the size of the testes. It turned out, the larger the testes, the larger the pelvic bone. Further, species that are more promiscuous tended to have larger penises and pelvic bones.
To ensure the size difference wasn’t just the result of a bigger whale, they also compared testes size with rib size, but there was no size correlation. Therefore, cetacean pelvic bone size, scientists say, is a direct result of sexual selection. They published their findings last week in the journal Evolution.
And, based on recent reports, it looks like blue whales in California are putting their pelvic bones to good use: their population is making a comeback from whaling.
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