The downsides of human evolution

Kate Lunau’s latest dispatch from the AAAS meeting

Content image

Kate Lunau is in Boston covering the 2013 annual meeting of the American Association for the Advancement of Science (AAAS), where some of the world’s finest brains and celebrities of science meet to mix, mingle, and share their latest and greatest ideas. On Feb. 14-18, she’ll give you a sneak peak into the current research—everything from dinosaurs to neutrinos, from stem cells to extreme weather, and all sorts of sorts of stuff in between. Follow her on Twitter: @katelunau, #AAASmtg

In a talk this morning on human evolution, I kept imagining that classic diagram of an ape transitioning to an upright human—and how it should show him hunched over in back pain, hobbling on a twisted ankle, on his way to the dentist to get his wisdom teeth removed. Evolution has put us at the top of the food chain, but “evolution doesn’t produce perfection,” anthropologist Jeremy DeSilva said today at the AAAS Meeting, where he spoke on a panel with others. Adapting to bipedal walking has left us with all sorts of aches and pains that no other animals seem to suffer, everything from hernias and flat feet, to fallen pelvic floors. He called these adaptations the “biological equivalent of duct tape and paper clips,” which affect us everyday.

Take our feet, which DeSilva studies: “The human foot isn’t something we’d design from scratch.” There are 26 bones in each of our feet, although they’d probably be much more effective if they were blade-like, similar to what paraplegic runners use. As we evolved to walking upright, we developed a range of foot problems, like fallen arches or bunions, which can’t simply be blamed on modern-day couch potatoism, sidewalks or footwear. In fact, we can see them dating back in the historical record.

Beyond just our feet, back pain is one of humankind’s most common ailments, said anthropologist Bruce Latimer. Over time, the switch to walking upright caused our spine to shift into an S-shaped structure. As we began to move around on two feet and our brains grew bigger, our head and face changed shape too, leaving our wisdom teeth with no room to grow, continued anthropologist Alan Mann. Some populations are less likely to have wisdom teeth: as many as 45 per cent of the Inuit lack third molars, he noted. Maybe unsurprisingly, the transition to a cushy modern lifestyle (which occurred on a very rapid timescale, as far as evolution goes) contributed to the rise in obesity, according to new research from William Leonard. Not only are our diets richer than ever before; we also move far less, which is an important contributor.

Humans give birth to large, big-brained babies. A newborn’s average size, relative to her mother, is about six per cent, said anthropologist Karen Rosenberg. For gorillas, it’s 2.7 per cent. Our babies’ brains continue to develop at a rapid rate even once out of the womb. The difficulty of birthing large, relatively helpless babies is made easier by the fact that we’re a cultural species, and help each other care for them once they’re born.

“Evolution is sometimes perceived as a dusty old science,” DeSilva said, “but it impacts us today.”