Our Actual “Eve”

She lived between 100,000 and 200,000 years ago in southern Africa. These days she is known as Mitochondrial Eve, but the “Eve” part is 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 every human today, male and female, can be traced back on his or her mother’s side—from daughter or daughters back to mother, back to the mother’s mother, and so on.

But interesting as such a linkage may be to scientists, how significant is Mitochondrial Eve for us? I’m not sure. See what you think.

Mitochondria produce energy. Originally independent cells themselves, they were engulfed by larger cells long ago and made themselves at home. They brought with them their own tiny DNA molecules that are unrelated to the DNA of the cell itself that make up our genes and reside in the cell nucleus.Mitochondria in a cell (Flickr)

Mitochondria in a typical cell. The long thread of genetic DNA in the nucleus is shown, but the unrelated DNA inside the mitochondria is not. (Flickr)

But the bits of DNA in the mitochondria, like genetic DNA, mutate over time; they change slightly as they copy themselves. These variations in a cell’s mitochondrial DNA were handed down through generations of pre-human primates and then early humans themselves, a trail of inheritance separate from our genes.

All of this is difficult to visualize. Here is a rough analogy. Automobiles have their own specialized energy component, the 12-volt battery that cranks the starter motor. Car batteries come in different brands and shapes with coded serial numbers and dates on them. Over the years, independently of yearly changes to cars themselves, battery manufacturers make changes to car batteries. Now imagine—it’s admittedly a stretch—that if you had no other way of knowing when a specific car model first went into production, you could get an approximate date by examining the style and code numbers on the car battery.

The variations in mitochondrial DNA serve a similar purpose. All humans inherit in only through their mothers. Males don’t pass theirs along. Why? Because the basic parts of our cells come from the woman’s ovum. Fathers deliver their genetic DNA by sperm to the egg, but the egg cell itself that divides into two cells, then four cells, and so on, is mom’s. Complete with her mitochondria.

Over the course of five thousand generations or so, women around the world passed their mitochondrial DNA, with its small but distinctive variations, 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. As if all lines of car batteries, in car models that changed or were discontinued, went out of production except one.

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 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, the biomedical historian Siddhartha Mukherjee writes in The Gene, “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  is the individual after which later 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 lived 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 is possible with some effort to envision the Most Recent Common Ancestor who looked a lot like us. Maybe Mitochondrial Eve’s value lies here: by thinking about her, we may be getting better at wrapping our heads around the reality of even older ancestors who seem impossibly ancient yet who made us what we are.

Who Were Homo Sapiens’ Parents?

Let’s imagine for a moment that you don’t know who your parents were. No records of them have been found yet. And because you don’t know your parents, you also don’t know for sure who your grandparents, great-grandparents or other direct ancestors were. But by some fluke you do know about some of your great-aunts and great-uncles, though none are alive now.

So you know about your general ancestry, where you came from, how your ancestors lived. But the family tree is complicated and you can’t be sure who your direct relatives were. You may be the offshoot of one of these aunts or uncle for all you know, you may be the result of a one-night fling or other scandalous pairing, or maybe your parents and grandparents just haven’t shown up in the records…yet.

Such a situation is where we stand with our species as a whole. We were “born” as a species when our bodies reached their present proportions about 195,000 years ago. Here’s a basic  version of the family tree around us and just preceding us, with some species omitted. There isn’t complete agreement on it, and it keeps changing as new bones and DNA samples come in.

  • Homo habilis (“handy man”) might be viewed as our great-great-grandfather (the masculine here will stand for both genders). He was good with tools and lived in Africa from 2.5 million years ago to 1.4 mya.
  • His descendant or cousin, Homo ergaster (“working man,” even better with tools) lived at about the same time,  1.9 to 1.4 mya.
  • homo_heidelbergensis-wikipedia-com

    Homo heidelbergensis (wikipedia)

    One of H. ergaster’s descendants was our grand uncle, Homo erectus, the first to stand tall and erect. Overlapping with our origins and a dominant presence in our past. H. erectus lived a long life not only in Africa but in Asia as well until 70,000 years ago. He used fire and he cooked. He lived in small, organized bands of families. He was thought to be our parent for a while but today the connection looks shaky.

  • The strong contender for our immediate ancestor at present is Homo heidelbergensis, an offshoot of the handy man H. habilis. H. heidelbergensis lived about the same time that we appeared.
  • Some H. heidelbergensis migrated into Europe where they evolved into the Neanderthals, our genealogical brothers or cousins. When we H. sapiens later migrated out of Africa, some of us lived near H. neanderthalensis, interbred with them (today almost all of us have a little Neanderthal in our genes), and survived them.

It’s a stunning story, all the more so because where we connect to it is still uncertain. The traits that we recognize as us—the abilities to walk and run, the skillful eye-hand coordination, the smarts to keep track of who to trust and who not to, our abilities both to exchange gossip and to discuss philosophy—all appeared step by step through such interesting early versions of us. And imagine being Homo erectus, with curiosity about how to chip a slightly sharper edge on your cutting stone or the skill to try out slightly different sounds as you talk to others. Or hearing the rumor that a group of men that look a little different than you, men who seem more organized and who carry longer spears, were appearing in the next valley.