Since Darwin, we have considered our bodies to be an outcome of natural selection. But recent anthropological theories suggest that our own technology, even the most primitive, may have affected our own evolution, right down to our shape.
1. Stones and rough tools
“Stone tools are basically artificial teeth,” says anthropologist John Shea. Named Oldowan, after the site in Tanzania where they were discovered, the oldest known tools date back 2.6 million years. The pebble cores, which range in size from a soccer ball to a golf ball, and flakes as small as a quarter, could have been used to help early humans pre-masticate their food, Shea says.
“Our teeth are not well suited to meat,” says another anthropologist, Peter S. Ungar. Human evolution, he says, can be divided into roughly two parts. During the first half, the time of Australopiths, our ancestors’ molar teeth got bigger, stronger, and thicker. Difficult to chew foods—think beef jerky or raw steak— would strain the jawbone, stimulating bone-building cells to form stronger and lengthier jaws. Two and a half million years ago, our genus Homo split away from Australopithecus and “bucked the trend,” using tools to process more food outside of the mouth, Ungar says. “They reversed it, they over time developed smaller and thinner teeth with slightly, slightly sharper crests.”
“I believe the transformative moment that gave rise to the genus homo, one of the great transitions in the history of life, stemmed from the control of fire and the advent of cooked meals,” writes Richard Wrangham.
2. Baby Slings
When early humans became bipedal, their pelvises grew narrower, causing babies to be born with smaller heads—and therefore with an extended need for parental care post-gestation.
At the same time, evolutionary changes in our hands and feet, along with a loss of body hair, prevented human infants from clinging to their moms. Baby chimpanzees can grip the fur of their mother, points out archaeologist and anthropologist Timothy Taylor, author of The Artificial Ape, but “compared to a chimpanzee infant, our children are even more helpless.” Lugging offspring became an energy hog. Australopithecine and early genus Homo moms spent around 20 percent of their energy carrying their young. Coupled with another 20 percent required for producing milk, taking care of an infant demanded close to half their energy.
baby sling, possibly made out of dried animal viscera, solved this problem,
Taylor says, and would allow babies to continue developing after birth. This,
in turn, helped us develop a higher intelligence outside the womb.
“It is, I believe, the thing that makes us human,” Taylor writes in his book.
3. Cooking and fire
“I believe the transformative moment that gave rise to the genus Homo, one of the great transitions in the history of life, stemmed from the control of fire and the advent of cooked meals,” writes anthropologist Richard Wrangham in his book Catching Fire: How Cooking Made Us Human.
Cooking increased the amount of energy derived from food while making it softer and easier to chew, he says. This was reflected in bodily changes—smaller guts, narrow pelvises, and ribs that didn’t flare out. An abundant fuel supply also helped to maintain our glucose-hungry brains, which required a lot of energy. “Brains are one of the most expensive organs in the body,” he says. Our brain uses 20 percent of our energy although it represents only 2 percent of our body weight.
The control of fire was important for our ancestors to get out of the trees and onto the ground. “To sleep on the ground would be extremely dangerous and something that no other primate does,” he says. Fire offered the ability to see and thus to defend against predators.
4. Cooperative foraging and hunting
“Don’t fire until you see the whites of their eyes.” This well-known Revolutionary War quote may hint as to why humans developed a uniquely white sclera, paler than their faces. Hiromi Kobayashi and Shiro Kohshima investigated this phenomenon in their comparative study of human versus other primate eyes. Out of 92 primate species they examined, 85 had brown or dark brown sclera.
Kobayashi and Kohshima also note that a human’s “eye outline is extraordinarily elongated in the horizontal direction.” These traits make it “very easy to discern the gaze direction in humans, in contrast to the gaze-camouflaging eyes of other primates,” they write. The ability to follow other humans’ eyes and the clues they give may have helped us develop cooperative skills like hunting. Other primates may have developed darker sclera to hide their gaze from predators.