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.

 

My Genome and Me

Recently I sent a DNA sample on two Q-tips swabbed inside my mouth to the National Geographic genome project. The information I received back described the whereabouts of my ancestors over the last 50,000 years or so. I’d known bits and pieces about my parents’ parents, all from different parts of Europe. But the DNA analysis showed me when their own early ancestors came to Europe out of Africa and what groups they belonged to when they got there.

Long before their journey, about 2 million years ago, earlier human species began migrating from Africa. Then about 60,000 years ago Homo sapiens began crossing Egypt and the Arabian peninsula. When we got to Europe, our cousins the Neanderthals were settled there and we settled down with them. Really, with them. My genetic make-up is 1.1% Neanderthal, which is the average for modern day non-Africans.

(crystallines.com)

(crystallines.com)

The genome report goes on to describe the two particular migrations on my mother’s and father’s sides out of Africa. On my father’s side, Branch H5 spread into Central Asia to points east and west, around 10,000 years ago. Today, H5 genes are common around the Black Sea and less so throughout Europe. Viking King Sven Estridsen, born in England but king of Denmark from 1047 to 1074, belonged to this group. He may have been one of my ancestors, but more likely he collected tribute from them.

On my mother’s side, Branch L2, about which less is known, left their genetic marker most frequently in Algeria, in northern Africa, but also in Asia and Europe, routes indicated quite clearly on the inset map.

Finally, there is my more recent regional ancestry, the combined information about both parents connecting me to any of 18 population groups around the world six or more generations ago. My genome links to three such groups. Forty-one percent of my DNA is descended from the Jewish Diaspora, the dispersal of Jews from the Near East, in this case into Europe. Thirty-one percent comes from Southern Europeans, the original peoples of the northern Mediterranean Coast. Finaly, 28% comes from Scandinavians, the most recent of the groups, since that area was peopled only after its glaciers melted around 12,000 years ago.

I’ve shared these results with family and friends, with mixed responses. Some find them too general to mean much. But they’ve also set off alarms about the pitfalls of knowing such information—about oneself or about others. The percentages and group identities make it tempting to imagine that a person is the way he or she is because of his or her ancestry—that I’m studious, for example, because of Jewish ancestry. A TV commercial shows a man who enjoys Swiss dances and lederhosen and who then finds from his genome that he is Scots, so he quits the lederhosen and takes up kilts. As if his genes made him suited for one but not the other. Did he feel it would be inappropriate or hypocritical to continue in the lederhosen? That seems not just silly but a little frightening. His genes are not him, not his abilities, not his interests.

True, some physical features, some potential abilities, and predispositions to some diseases are inherited. But our specific and individual characteristics depend as much if not more on the web of family, community, and culture and the flux of time. Saying a person has a specific characteristic because of his ancestral group is a shade less inaccurate than saying he has it because of his astrological sign.

For me, the genome history helps fill in my reveries about ancestors leading their particular lives a very long time ago. I picture a family walking in Eastern Europe, another farming in Italy, or a group crossing the water from Denmark, none of them knowing that far in the future, the paths of their descendants will come together in me. I imagine myself greeting them from their future and watching their surprised smiles as they realize who I am and as I tell them how often I’ve been thinking of them.

Walk, Run, Eat: The Evolution of Our Body

It can be difficult to visualize the stages that led from our chimp ancestors to the body that we see in the mirror. 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 feet, legs, arms 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 tchadens, 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 has been 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 australopithicus 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, and still with relatively long arms and short legs.

The next stage 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 and made it chewable and digestible. We became taller, with arms and legs close to today’s proportions. We developed external noses to humidify the air that 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” such as diabetes and other conditions like hardening of the arteries that our ancestors had no need to adapt to. We may treat the symptoms successfully, but we ignore the reality that, given evolution’s slow clock, we won’t be adapting to resist them any time soon.

march of progress

The original version of the “March of Progress,” from Time magazine in 1965. The details are out of date now and the notion of linear, progressive development has been criticized. But the image remains indelible.
(Wikipedia)