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.

 

“Your Inner Fish”

Most people accept the idea that we are descended from earlier primates. But descended from fish? That might seem to be a stretch. In Your Inner Fish: A Journey into the 3.5-Billion-Year History of the Human Body (2008), Neil Shubin makes a vivid case. He traces our body parts back to fish and beyond. And he comments passionately on the beauty and unity of life’s development over billions of years.

tiktaalik

Tiktaalik, ready for push-ups–and land
(shubinlab.uchicago.edu

Along the way, Shubin narrates the painstaking detective work of the paleontologist. He weaves the opening chapters around his own years in the barren Arctic as he helped to discover, in 2004, the 375-million-year-old fossil of a missing link between fish and amphibians.

The discovery  of Tiktaalik, Inuit for “large freshwater fish,” was exciting for several reasons:

All fish prior to Tiktaalik have a set of bones that attach the skull to the shoulder, so that every time the animal bends its body, it also bent its head. Tiktaalik is different. The head is completely free of the shoulder. This whole arrangement is shared with amphibians, reptiles, birds, and mammals, including us. The entire shift can be traced to the loss of a few small bones in a fish like Tiktaalik. (p. 26 in the Vintage paperback edition).

Say hello to our neck.

neck

In the middle, Tiktaalik’s new neck.
(avonapbiology.wikispaces.com)

There was another surprise about Tiktaalik. Earlier fish had fins with bones that were the ancestors of our arms and fingers. To these early forearms and fingers Tiktaalik added small bones that were, in fact, the earliest wrists. These crude wrists mean that Tiktaalik, as Shubin puts it, “was capable of doing push-ups….The wrist was able to bend to make the fish’s ‘palm’ lie flat against the ground….Tiktaalik was likely built to navigate the bottom and shallows of streams or ponds, and even to flop around on the mudflats along the banks” (39-40).

So Tiktaalik had fins capable of supporting the body—these were the first limbs for moving on land. Since then, the same structure has appeared in not only the arms, legs, and hands of humans and other mammals but also in the wings and flippers of bats, penguins, birds, and whales. In all these, one bone is attached to the torso (in us, the upper arm bone and the upper leg bone), followed by two bones, followed by little bones (wrists and ankles), followed by smaller fingers and toes.

limb bones

Limb bones from fish to humans
(noreligionblog.wordpress.com)

Shubin’s other chapters trace the development of teeth, heads, noses, eyes, ears, and even bodies themselves, which emerged 3.5 billion years ago. In each chapter at some point, Shubin pauses to explain his appreciation of the patterns he is describing. “Beauty” and “beautiful” are common words in the book. The anatomy of the head “is deeply mesmerizing, in fact, beautiful. One of the joys of science is that, on occasion, we see a pattern that reveals the order in what initially seems chaotic. A jumble becomes part of a simple plan, and you feel you are seeing right through something to find its essence” (82). Echoing Carl Sagan’s thought that “looking at the stars is like looking back in time,” Shubin says the same about the human body. “If you know how to look, our body becomes a time capsule that, when opened, tells of critical moments in the history of our planet and of a distant past in ancient oceans, streams, and forests” (184).

I would guess that many scientists feel the same way about looking into the essences behind the apparent chaos. But not many write about it so well. That’s unfortunate, because I think that if they did, more non-scientists would value what our biological history can tell us about who we are and what our lives mean.