We Are All Descended From an Actual “Eve.” So?

She lived between 100,000 and 200,000 years ago in southern Africa. These days she’s known as Mitochondrial Eve, but that’s a little misleading. Unlike the Biblical Eve, she wasn’t the first woman nor was she the only woman alive at the time—and there were plenty of men around as well. Still, Mitochondrial Eve was an actual person. We don’t know much about her except that she is the most recent woman to whom everyone alive today—male and female, all 7.6 billion of us—is connected through their mothers by a speck of DNA.

But as important as such a linkage may be to scientists, how significant is it for the rest of us? Frankly, I’m not sure. See what you think.

Every cell in any organism contains small particles that keep the cell alive. The  nucleus, with the genetic DNA masterplan of the body, is the cell’s control center. Smaller particles carry out other functions. Mitochondria produce energy for the cell. They contain their own, separate, bit of DNA because millions of years ago they were free-floating bacteria that were absorbed by cells, proved useful, and took a permanent place in the cell anatomy.

Mitochondria in a cell (Flickr)

Mitochondria in a typical cell. The long thread of genetic DNA in the nucleus is shown but not the bits of mitochondrial DNA, which are incidental and much smaller. (Flickr)

Over time and countless cell divisions, and separate from any mutations in the genetic DNA, the DNA in the mitochondria also changed in small ways. As a result, the early apes, then the pre-humans, then the earliest modern Homo sapiens all carried the slight variations in mitochondrial DNA that they inherited.

But they inherited them only through the females. Males couldn’t pass theirs along. Why? Because we inherit our cellular structure from mom’s egg. While men may deliver their genetic DNA by sperm to the egg, it’s mom’s egg cell itself that grows into the embryo and into all human cells. Complete with the mother’s mitochondria.

Over the course of five thousand generations or so, women around the world passed their variations of mitochondrial DNA to their daughters. Along the way, though, some mothers bore only sons and other women had no children at all. Gradually, all the variations of mitochondrial DNA fizzled out, except one. We all carry it, as did a woman a long time ago, Mitochondrial Eve.

What to make of all this? Compared to the Biblical Eve and her list of firsts—first woman, first human to be curious, first mother—we have little to show for our ancestry from the other Eve, Mitochondrial Eve. And the merging of genetic DNA from our mother and father has by far a greater influence on who we are and what we’re like. By comparison, Mitochondrial Eve is just a woman a very long time ago whom we all happen to be linked with inconsequentially on our mother’s side.

Still, as Siddhartha Mukherjee writes in The Gene, without elaborating, “I find the idea of such a founding mother endlessly mesmerizing.” For Mitochondrial Eve is one of our Most Recent Common Ancestors–an MRCA. The MRCA for any group of organisms, whether the same species or not, is the individual or type after which subsequent generations evolved in different directions. The MRCA of primates (humans as well as chimps, apes, monkeys, baboons) lived 65 million years ago. The MRCA of all animals, 600 million years ago. And the MRCA of all living things, 3.6 billion years ago. For many people, interesting to know but not so easy to imagine.

But it’s a little less difficult to imagine in the case of the most recent MRCA, the one who looked a lot like us. Maybe Mitochondrial Eve’s value lies here after all: by thinking about her, we may be learning to wrap our heads around the reality of many ancestors who seem impossibly ancient yet who made us what we are.

Walk, Run, Eat: The Evolution of Our Body

Visualizing the evolution of our bodies from our chimp ancestors to what we see in the mirror does not come easily. But Daniel E. Lieberman’s The Story of the Human Body: Evolution, Health, and Disease is a fine time machine. It took me back six million years to changes in our feet, legs, arms, head and torso, all molded as our ancestors searched for food.

Reconstruction of sahelanthropus tchadens, who lived six to seven million years ago. (smithsonianscience.org)

Reconstruction of Sahelanthropus tchadensis, who lived six to seven million years ago. Not your average chimp. (smithsonianscience.org)

Human evolution can be said to have begun when one of our ancestors developed a feature that is still unique to us: We walk on two legs. That ability separated us from our cousin chimps between six and seven million years ago. We remain the only two-footed walking animal that doesn’t carry the feathers of a bird or the tail of a kangaroo.

Why walk? We began walking when the fruit that we ate became sparser. The African continent was cooling and the forests were shrinking. (I’ve conflated the species that Lieberman names to “us.”) Those who could stand upright and walk distances on two feet found not only more fruit but also edible stems and leaves. We were chimp-size, but as bi-pedal walkers our arms and hands became free for new uses.

intermediate human

A reconstruction of Australopithecus bosei, “Nutcracker Man,” who lived two million years ago, discovered by Mary and Louis Leakey in 1959. Our intermediate stage. (Wikipedia)

The transition continued. By four million years ago, our anatomy had changed again. Foraging over distances fostered “more habitual and efficient long-distance walking.” Our feet acquired an arch that put a spring in our step and pushed the body forward. For stronger chewing, molars and jaws became much larger than ours today. These ancestors are nicknamed “Nutcracker Man.” We were still small but more upright, still with relatively long arms and short legs.

Next was the Ice Age, two and a half million years ago. Foraging over larger areas required more calories, calories that meat could provide. Our ability to throw accurately brought down animals. Sharp stone tools cut up their flesh to make chewable and digestible. We grew taller, with arms and legs close to today’s proportions. We developed external noses that humidify the air we inhaled during long walks. We began to run—far—with Achilles tendons for more spring and unique sweat glands and finer fur to stay cool.  As teeth and snouts shrank and brains grew, heads became rounder. Organized hunting and gathering became necessities. Generally, females gathered while males hunted. Unlike chimps, we shared food readily with extended families. Cooperation, coordination, and communication were means of survival. We—Homo erectus—became “significantly human.” 

homo erectus

Homo erectus reconstructed.
“Significantly human,” writes Lieberman. (Wikipedia)

Lieberman continues the story of our evolution into the present and discusses its relevance to disease. After millions of years of seeking food and storing its energy in our bodies whenever we could find it, today we eat more calories than we need while we burn off fewer calories than ever before. As a result we suffer from “mismatch diseases” like diabetes and conditions like hardening of the arteries that our ancestors never worried about. We may treat the symptoms successfully, but given evolution’s slow clock, we won’t be adapting to resist them any time soon.

But we are always walking. We walked our way into becoming human, we walked our way around the world and into history, we speak of journeys, progress, protest marches. There is little else we do that is more essentially us.

march of progress

The original version of the “March of Progress,” from Time magazine in 1965. The details are out of date now but the image remains indelible.
(Wikipedia)