Monday, October 09, 2006

Chimps and Humans Evolved From a Common Ancestor?

This is an excerpt from "The Wonder of the World." Also the 2% difference translates into 35 million specific genetic differences (cf. story last week on Neanderthal DNA).

Geek: I have to agree that you’ve raised inescapable issues on the mechanisms of evolutionary change. Let me take a different tack: your whole thesis of supernal interventions faces rough sailing when we get to homo sapiens. As you no doubt know, chimps and humans evolved from a common ancestor. Chimpanzees and human beings, in fact, share 98% of the same DNA. So the culmination of the evolution of life, the grand finale, is a glorified ape!

Guru: Let me first address the widely publicized 98% issue.

What conclusions do you draw from the fact that we share 98% of our DNA with chimpanzees? In his acclaimed What It Means to Be 98% Chimpanzee: Apes, People and Their Genes, the anthropologist Christopher Marks has given us a superb overview of the illicit premises and inferences that lead in general to false genetically-based explanations. The 98%statistic is just one more such red herring. “In the 1990’s,” writes Marks, “we routinely heard that we are just 1 or 2% different from chimpanzees genetically, and therefore … what? Should we accord chimpanzees human rights, as some activists have suggested? Should we acknowledge and accept as natural the promiscuity and genocidal violence that lurks just beneath the veneer of humanity and occasionally surfaces, as some biologists have implied? Or should we perhaps all simply go naked and sleep in trees as the chimpanzees do? None of these suggestions, of course, necessarily follows from the genetic similarity of humans to apes, although the first two have been proposed within the academic community and promoted in the popular media over the past few years.”

So what, he asks, “does the genetic similarity of apes to men mean? What is it based on? Does it have profound implications for our understanding of human nature? Here we will see that the universe of genetic similarities is quite different from our preconceptions of what similarities mean. For example, the very structure of DNA compels it to be no more than 75% different, no matter how diverse the species being compared are. Yet the fact that our DNA is more than 25% similar to a dandelion’s does not imply that we are over one-quarter dandelion – even if the latter were a sensible statement. This will be the primary illustration of the confrontation between scientific data and folk knowledge, and of the exploitation of the latter by the former. The extent to which our DNA resembles an ape’s predicts nothing about our general similarity to apes, much less about any moral or physical consequences arriving from it.”

We cannot draw any conclusions about the relation of anything that chimpanzees do to anything done by humans, says Marks, because we still lack the detailed physiological and genetic data and analyses required. “ Since they have been different species for several million years, anything that chimpanzees do may be either (1) an element shared with human nature; or (2) an ancient element of human nature now lost by humans; or (3) an evolved element of chimpanzee nature, never possessed by human ancestors.” In brief, as Marks said in an interview, the fact that an animal shares 98% of its DNA with humans does not mean it is 98 percent human.

Moreover, most of the DNA we share with chimpanzees is the non-coding or “junk” DNA (DNA that doesn’t code for proteins).

Elaine Morgan draws our attention to the big picture: “Considering the very close genetic relationship that has been established by comparison of biochemical properties of blood proteins, protein structure and DNA and immunological responses, the differences between a man and a chimpanzee are more astonishing than the resemblances. They include structure differences in the skeleton, the muscles, the skin, and the brain; differences in posture associated with a unique method of locomotion; differences in social organization; and finally the acquisition of speech and tool-using, together with the dramatic increase in intellectual ability which has led scientists to name their own species Homo sapiens sapiens – wise wise man. During the period when these remarkable evolutionary changes were taking place, other closely related ape-like species changed only very slowly, and with far less remarkable results. It is hard to resist the conclusion that something must have happened to the ancestors of Homo sapiens which did not happen to the ancestors of gorillas and chimpanzees.”