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More on male vs. female body form and Darwinian sexual selection


Recently, we noted a dissent from Darwinian sexual selection on male vs. female form by U Rhode Island prof Holly Dunsworth. It turns out that Chase Nelson also weighed in on that:

There is no evidence to support the assumption that mechanically efficient bipedal walking requires a narrow pelvic morphology. If there are metabolic costs to walking and running with wider hips, they could be offset by subtle changes in movement patterns. Nor is brain size necessarily the primary cause of birth complications; fetal shoulders are also very broad and, like the head, require rotational movements for passage through the birth canal.

In a 1992 review, Allan Wilson and Rebecca Cann argued that genetics provides a better approach to human origins than paleontology. While “living genes must have ancestors,” they wrote, “dead fossils may not have descendants.” The genome is a matter of fact, but the fossil record requires interpretation.

Chase Nelson, “The Obstetrical Dilemma” at The Inference Review

Most of his article deals with the more fascinating topic of the development of the human brain:

Human infants have brains roughly one third the size of adult brains; for chimpanzees, the figure is much higher, at roughly 40%.43 At 16 weeks of gestation, the human brain is twice the size of the chimpanzee brain. After 22 weeks of gestation, chimpanzee rates of growth slow and human rates of growth accelerate. At 400cc, human newborn brains are roughly 2.7 times larger than chimpanzee brains.44 Since maternal energy demands increase exponentially during human fetal development, waiting longer than nine months would exceed the maximum sustainable maternal metabolic rate, which is approximately the same across primates.45 Other mammals rely on progesterone depletion for the initiation of birth, but primates give birth when progesterone levels are at their height. It is an energetic ceiling that signals the onset of labor.

Chase Nelson, “The Obstetrical Dilemma” at The Inference Review

And much more.

See also: A new challenge from an anthropologist to cozy Darwin tales about men vs. women. Holly Dunsworth seems to have actually researched the literature rather than signing on to the narrative.


Rob Sheldon offers some thoughts on the recent challenge to Darwin’s sexual selection. Sheldon: Finally, somebody is saying what ID has claimed for decades–Darwin has no clothes. It’s just-so stories stacked on just-so stories with the very thinnest of experimental evidence. And that’s the only thing I admire about post-modernists.

All this stuff about mechanical efficiency and metabolic efficiency is meaningless. Nature doesn't work that way. Nature has a PURPOSE for everything, and finds a way to accomplish the purpose with the available equipment. The way is sometimes efficient but more often wildly extravagant. Minimum energy is simply an irrelevant variable. We've gotten in the habit of using it because we can measure it reliably. That's where the streetlight is.polistra
August 16, 2020
08:17 AM

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