Our Actual “Eve”

She lived about 150,000 years ago in southern Africa. These days she is known as Mitochondrial Eve. The “Eve” part is a little misleading since unlike the Biblical Eve, Mitochondrial Eve wasn’t the first or only woman alive at the time, and there were also plenty of men around. Still, Mitochondrial Eve was an actual person to whom every human today, male as well as female, can be traced back on his or her mother’s side—from mother to mother’s mother and so on.

But interesting as such a linkage may be to scientists, how significant is Mitochondrial Eve for us? See what you think.

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)

Mitochondria (my-de-KAHN-dree-ah) are particles inside of cells that produce energy for the cell. Originally independent cells themselves, mitochondria were engulfed by larger cells long ago, proved useful, and made themselves at home.

When they did so, mitochondria brought with them their own bits of DNA. These strands are not related to, and are much smaller than, the complex DNA in a cell’s nucleus that make up our genes. But like all DNA molecules, as mitochondrial DNA makes copies of itself, it sometimes mutates; copying errors occur and the DNA changes slightly. As a result, mitochondrial DNA, handed down through generations of female humans, forms a record of our ancestry separate from our genes.

If this is difficult to visualize, a rough analogy is the battery in a car. These 12-volt energy-units that power the starter motor come in different brands with serial numbers and other codes on them. Over the years, independently of changes in cars themselves, battery manufacturers make changes to car batteries. Now imagine that you had no other way of telling the age of a car that had, say, been crushed beyond recognition. One option w ould be to dig out what was left of the car battery to find its codes or numbers. The car battery would date the car.

But if a particular version of mitochondrial DNA is passed down through women, how is it that males also carry it?  Because this DNA comes in the cell that each human grows from, and that cell is our mother’s. Fathers, through their sperm, contribute some of the genetic DNA that creates the new person, but the cell that begins to divide and multiply is mom’s, complete with her formulation of mitochondria DNA.

At the time that Mitochondrial Eve lived, of course, other mothers were passing along their own mitochondrial DNA to their own children, to their daughters’ children, etc. What happened to all those versions? Why is it that today’s humans everywhere carry the same version, the same mutation, of mitochondrial DNA? Apparently all those other lines of mitochondrial DNA fizzled out. Some mothers bore only sons, with no daughters to carry on their cell line. Other women had no children at all. The single remaining “brand” of mitochondrial DNA has been traced back to an approximate place and time five thousand generations ago. It is as if over the years all brands of car batteries went out of production except one, and that one is now installed in all cars.

What are we to make of all this? Compared to the Biblical Eve and her list of firsts—first woman, first human to be curious, first mother—Mitochondrial Eve wasn’t a forerunner of any of our significant traits. It’s that other  DNA, the genetic DNA from our mother and father, that plays a role in the color of our eyes and our musical aptitude.

Still, as biomedical historian Siddhartha Mukherjee puts it The Gene: An Intimate History:  “I find the idea of such a founding mother endlessly mesmerizing.”

It is mesmerizing to know that a small identifier in each of us can be traced back to a single human mother long ago. In theory, any diverse group of living things has a common ancestor after whom its descendants branched off. But that common ancestor may be difficult to “relate” to. The ancestors of all primates (not only humans but also monkeys, baboons, and chimps) lived about 60 million years ago and looked something like a squirrel with large eyes. I don’t feel the warmth.

On the other hand, I like the idea of being descended from a mother a long time ago from whom all other humans today are matrilineally descended as well, and whom we could, if we saw her, recognize as one of us.

Who Were Homo Sapiens’ Parents?

Let’s imagine 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 who some of your great-aunts and great-uncles were. Because you know a little about them, you know about your general ancestry, where you came from, how your ancestors lived. Still, the family tree is complicated and incomplete when it comes to your own parents. You may be the offshoot of one of these aunts or uncle for all you know.  You may be the result of a fling or other scandalous pairing. Or maybe your parents and grandparents just haven’t shown up in the records yet.

This is about 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

    H. heidelbergensis. Hello, Dad? (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 has been thought to be our parent for a while but today the connection looks shaky.

  • The strongest 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 members of 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 us), and survived them.

It is 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 these early versions of us.

And imagine being our great-uncle H. 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 people that look a little different than you—a little taller, with shorter hair—were walking through the next valley.