Human = Chimp

In a piece at ENV, biologist Ann Gauger debunks the notion, widespread in the popular press, that humans and chimps are genetically almost identical. The oft repeated figure is that the two species share 99% of their genes which implies a very close evolutionary relationship. There are numerous faults with this reasoning, however. Gauger explains:

You have probably heard that our DNA, the stuff that makes us human, is only 1% different from chimps. The claim that we are little more than apes is now part of the Zeitgeist of our culture, having been propagated in the popular press for nearly forty years. However, that statement and the conclusions drawn from it are false.

Let's look at the first claim, that we are only 1% different from chimps. That measurement only compares base changes in human and chimp DNA. It doesn't include other kinds of changes to the DNA, like deletions and insertions or rearrangements. In addition, because of the sequencing methods used, repetitive DNA is not included. Now that complete or nearly complete genome sequences for humans and chimps are available, a better picture of our differences and similarities is emerging. A 2007 essay in the journal Science, says this:

Researchers are finding that on top of the 1% distinction, chunks of missing DNA, extra genes, altered connections in gene networks, and the very structure of chromosomes confound any quantification of "humanness" versus "chimpness."

To be specific, in addition to the 1% distinction already noted, entire genes are either duplicated or deleted between the two species, sometimes in long stretches called segmental duplications. Such duplications represent a 6.4% difference between chimps and humans. There are also insertions and deletions within genes, which affect the structure and function of the proteins they encode. That contributes another 3%, according to some estimates. And there are entirely new genes, specific to humans.

This is just the beginning of the differences. Go to the link for the rest of Gauger's catalog of variances between the two species. The reason some are so interested in showing a close genetic relationship between humans and chimps, of course, is the more closely we are alike genetically the easier it is to draw the conclusion that we are biologically related and descended from a common ancestor.

This is predicated on the assumption, however, that DNA is what makes species different (or alike). Evidence is mounting that DNA is only one factor, maybe not even a major factor, in establishing the characteristics of a species. Gauger talks about some of these other factors and then concludes:

And that brings me to another false assumption underlying the mismeasure of man -- that genes make us who we are. Many things beyond our genes contribute to making us who we are. Our genes do not control us. Certainly, they can influence our predisposition to disease, the shape of our nose, or the color of our eyes, but they do not specify how we will respond to the challenge of disease, or what spouse we will choose.

Our experience and our moral character have something to contribute to those things. New studies in psychology indicate, for example, that we can rewire our own brains to think in new patterns; those new thoughts actually change the underlying neural connections. The choices we make matter. And this is a very non-Darwinian thought.

None of this means that chimps and humans did not descend from a common ancestor, but what it does mean is that there's good reason to doubt the notion, common in some circles, that we are "just" a naked ape, that we are "just" an animal pretty much like every other mammal. It also confirms the suspicion that so much of what we thought we knew about our evolutionary past is simply not true.