From the “Yes, a researcher really said that in a real study” file comes this observation from a female evolutionary biologist who claims that the wide pelvis she and her fellow females of the human species have came from ancestors who once laid eggs instead of giving birth to live babies. Don’t worry, this is not a treatise on the modern day gender identity debate, so we can all set aside our differences for a moment, join hands and raise our voices in a hearty “Wait … WHAT?”
“It is commonly assumed that the strong sexual dimorphism of the human pelvis evolved for delivering the relatively large human foetuses.”
Evolutionary biologist Barbara Fischer lead a team from the University of Vienna, the KLI for Evolution and Cognition Research, and the University of Calgary in research that became the study “Sex differences in the pelvis did not evolve de novo in modern humans” published this week in the journal Nature Ecology & Evolution. They start with one of those accepted theories that never seemed debatable – human females have wider pelvises and hips than human males because they give birth to huge babies with huge heads. That pattern probably holds true when one looks back at human ancestors and cousins like the Neanderthals, but Fischer’s team went sideways and noticed that similar mammals, like chimps and apes, also have wide pelvises but give birth to smaller babies so easily that they have no grunt that means “Call a midwife!”.
That’s interesting, but what about women laying eggs?
The explanation, like the eggs, is coming. The researchers then looked at the pelvises of non-ape mammals and found that some, like bats and some primates, give birth to larger fetuses like humans, while others, like cats and opossums, give birth to tiny babies. Yet all show differences, sometimes subtle, between the pelvises of males and females. That led them to look at common evolutionary ancestors, a search that found pelvic differences between the sexes dating WAY back.
“In our paper, we show that the evolutionary pattern of a sexually dimorphic pelvis [differing between the sexes] has not been developed by modern humans but is inherited from our ancestors and it might indeed stem from early mammals or amniotes [other animals such as birds and reptiles], who laid large eggs or gave birth to large fetuses.”
In an interview with Daily Mail, Dr. Fischer gives the unusual big reveal – wide female hips come from reptilian ancestors that laid eggs. However, as the evolutionary tree split off mammals, the need for egg-wide hips went away but the wide hips didn’t. That came in handy when some primates began to grow the large brains and necessary big heads that made them humans – their mothers’ hips were ready for them.
Well, when you put it that way, it makes sense … doesn’t it? While laying eggs like platypuses and echidna – the only mammals that still do it – would make for less messy birth videos, it would require even longer pregnancy leaves than most employers are willing to give. And, with the resistance to breast-feeding in the workplace, imagine trying to convince your employer to allow you to sit on eggs while doing your job.
It’s good that human females have wide hips to accommodate our big heads. If only our brains took advantage of all that space.