Ouch. Shin splints are just part of the joy of being human.

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Human Evolution: Gain Came With Pain

BOSTON—Humans are the most successful primates on the planet, but our bodies wouldn’t win many awards for good design. That was the consensus of a panel of anthropologists who described in often-painful (and sometimes personal) detail just how poor a job evolution has done sculpting the human form here Friday at the annual meeting of AAAS (which publishes ScienceNOW). Using props and examples from the fossil record, the scientists showed how the very adaptations that have made humans so successful—such as upright walking and our big, complex brains—have been the result of constant remodeling of an ancient ape body plan that was originally used for life in the trees. “This anatomy isn’t what you’d design from scratch," said anthropologist Jeremy DeSilva of Boston University. "Evolution works with duct tape and paper clips."


A better design for upright walking and running, DeSilva said, would be a foot and ankle like an ostrich. An ostrich’s ankle and lower leg bones are fused into a single structure, which puts a kick into their step—and their foot has only two toes that aid in running. "Why can’t I have a foot like that?" asked DeSilva. One reason is that ostriches trace their upright locomotion back 230 million years to the age of dinosaurs, while our ancestors walked upright just 5 million years ago.

Turning up the pain threshold a notch, anatomist and paleoanthropologist Bruce Latimer of Case Western Reserve University in Cleveland, Ohio, limped to the podium, dangling a twisted human backbone as evidence of real pain. "If you want one place cobbled together with duct tape and paper clips it’s the back," said Latimer, a survivor of back surgery.


Paleoanthropologist Karen Rosenberg of the University of Delaware, Newark, moved beyond pain. As our bodies had to adapt to upright walking and bigger brains, they had to balance both of those changes with the limitations of the birth canal—and allowing enough mothers and babies to survive that the big-brained, upright walking species didn’t go extinct. "Death in childbirth used to be leading cause of death for women in reproductive years." That’s because compared with other primates, humans give birth to babies with larger bodies and brains—on average, human babies are 6.1% of their mother’s body size compared with chimp babies (3.3%) and gorilla babies (2.7%).

Despite the high risks for death and injury in childbirth, our ancestors’ solution to the problem was to give birth with social support. Today, humans rely on culture, often in the form of modern medicine, to change that outcome, using assisted birth with doctors or midwives, for example. One sign of that is that is that caesarean sections account for about 30% of all births in the United States, Rosenberg said.

The point of citing all these problems? Evolution doesn’t "design" anything, says anthropologist Matt Cartmill of Boston University, a discussant on the panel. It works slowly on the genes and traits it has at hand, to jerry-rig animals’ and humans body plans to changing habitats and demands. “Evolution doesn’t act to yield perfection," he says. "It acts to yield function.”