It happened again.
Every time a new fossil is described, a new science discovery makes it into the mainstream media, headline writers do their best to convince us that everything that came before is wrong, and this discovery, this find, changes science forever.
Today’s Dispatch carries the headline “Newest Fossil Shakes the Tree.” The article that follows is actually a pretty decent account of how Ardipithecus ramidus fits into the story of human evolution. “Ardi” does contain some surprises, but those surprises fit well into the story that has been developing now for some time.
The headline is almost clever, because it could refer to two different trees. First is the tree of evolution, showing how we have changed over time. Ardi doesn’t so much shake this tree as add another very interesting branch. But second is the “tree” that Ardi herself (and others like her, of course) actually lived in part-time. That’s an interesting finding, and it does push us in a particular direction.
The difficulty so many people have with evolution is summed up well by the famous line, “If humans evolved from apes, why are there still apes?” While it might draw a chuckle, the line displays more a profound misunderstanding of evolution than it does a profound thought. And Ardi brings the difficulty to light.
Our closest living ape relatives are chimpanzees, bonobos, and gorillas. All are more or less ground-living apes that walk on their knuckles. So did we evolve from ground-living apes that walk on our knuckles? With no other models, we might have thought so. But evolution doesn’t work that way. Chimps, bonobos, and gorillas are evolving, too. Six million years ago, when the human and chimp line split, the last common ancestor was not human, but neither was it chimpanzee.
Instead, Ardi indicates that this common ancestor probably was a smallish, tree-living creature with flexible wrists and ankles. It may have even been leaning toward some bipedality. Later, this creature’s descendents went in at least two directions. One direction was toward knuckle-walking, ground-living apes that became chimps and bonobos. The other was toward smaller, more upright walkers that became (in time) us.
The other interesting thing Ardi seems to show is that knuckle-walking, seen in both chimpanzee species as well as in gorillas, must have evolved separately at least twice. We and chimps are more closely related to each other than either is to gorillas. To me, this is one of the most amazing findings of science. We and chimps are close cousins, and gorillas are the outlyers of the group. To a gorilla, we and chimps are basically the same, just as to us horses and zebras are the same sort of creature.
Anyway, the point is that gorillas moved toward ground living and knuckle walking before our ancestor split with chimps, and that ancestor was apparently not a knuckle walker. So knuckle walking and all that comes with it – including larger size and distance covered – must have evolved separately in those chimp-like descendents.
The most amazing part of all this, of course, is not so much the facts themselves, but the fact that we humans, descendants of a tree-dwelling ape that lived some six million years ago, have awoken to this world, learned of the passage of time, and discovered that we can discover.
The powerful play goes on, and we may contribute a verse.
How’s that for a headline?