Proposed changes in the primate order are stirring up evolutionary debate. Humans and chimpanzees should be grouped in the same genus, Homo, according to WSU researchers in a May 19 article (#2172) published in the Proceedings of the National Academy of Sciences. Although WSU's Morris Goodman, PhD, has already proven with non-coding DNA sequences that chimpanzees are closest in kinship to humans rather than to gorillas, evolutionary traditionalists say chimps and humans are functionally markedly different and therefore belong on different branches of the family tree.

New analyses show humans and chimpanzees to be 99.4 percent identical in the functionally important DNA, which codes for proteins and is shaped by natural selection. This provides further evidence for revisions in our genus classification. Dr. Goodman proposes that all living apes should occupy the family Hominidae (which currently contains only humans), and that both humans and chimpanzees should occupy the genus Homo.

In traditional taxonomic schemes that are still widely employed, humans are classified as Hominids, while orangutans, gorillas, and chimpanzees are classified as Pongids. Genetically, however, chimpanzees are more closely related to humans than they are to gorillas. "The accumulating DNA evidence provides an objective non-anthropocentric view of the place of humans in evolution. We humans appear as only slightly remodeled chimpanzee-like apes," Dr. Goodman said.

The WSU research team compared 97 functional genes in six different species: humans, chimpanzees, gorillas, orangutans, old world monkeys, and mice. Based on genetic mutation tracking rates, the scientists constructed an evolutionary tree that measured the degree of relatedness among the six species.

Chimpanzees and humans were the most closely related, sharing 99.4 percent identity at nonsynonymous (functionally important) sites and 98.4 percent at synonymous sites (functionally much less important).

Researchers determined that humans and chimpanzees diverged from a common ancestor roughly five to six million years ago, which in turn diverged from gorillas about six to seven million years ago.

"Revisions to our classification system would have far-reaching implications, much more important, in fact, than proving that humans and chimps are barely divergent. Such revisions would ensure that objective scientific measures of similarity and dissimilarity are used, rather than anthropocentric, subjective observations. Sound genetic analysis should always be the basis for understanding the place of humans in evolution," Dr. Goodman asserts.

These taxonomic changes had been proposed previously by several evolutionary experts, including Dr. Goodman, but a difference of scientific philosophies is at play. Traditional anthropologists argue that chimps are functionally different than humans because, for example, they lack spoken language and their genetic disease susceptibilities are different.

In contrast, Dr. Goodman opens his article with a quote from Charles Darwin that says: "As we have no record of the lines of descent, the lines can be discovered only by observing the degrees of resemblance between the beings which are to be classed. For this object numerous points of resemblance are of much more importance than the amount of similarity or dissimilarity in a few points."

Dr. Goodman is a distinguished professor in the Wayne State University School of Medicine's Department of Anatomy and Cell Biology and the Center for Molecular Medicine and Genetics.

In 1962, he sparked great debate when he originally asserted that chimpanzees and gorillas are genetically more closely related to humans than to other apes. His research has since been widely accepted and his work in this area has not only impacted the study of humankind's place in nature, but also has important implications for medical science.


The full article, "Natural Selection's Role in Shaping 99.4% Nonsynonymous DNA Identity Between Congeneric Humans and Chimpanzees," is featured as article #03-2172 in the May 19-May 23, 2003 issue of the Proceedings of the National Academy of Sciences. It can be viewed online, beginning May 19, at PNAS Web site.

Co-authors on Dr. Goodman's inaugural PNAS article, since his 2002 election into the National Academy of Sciences, are: Derek Wildman, Monica Uddin, Guozhen Liu, and Lawrence Grossman.