BY LENORE PIPES

In print | Published November 2, 2006

I am obsessed with how we, as one of over 200 existing primate species, are ultimately dominating Earth. Derived from a consummate capacity for culture, this dominance has allowed us to become ecologically generalized and to disperse into a variety of niches across the globe.

The features that caused such a colossal change in the evolutionary trajectory of humans compared with other closely related primates obviously underlie the significance of human uniqueness. Many fail to realize that the actual genetic basis for the unique features of human anatomy (e.g., facultative bipedal locomotion, cranial enlargement, larynx structure), physiology (e.g., susceptibility to AIDS) and behavior (e.g., speech, higher order cognitive functions) are not currently known. However, we’ve known for a long time that all these features seem to have analogies in other primate species.

Even when it comes to genes, humans and chimps are so similar that some scientists have attempted to classify humans and African great apes together in a single genus. Decades of genetic comparisons have consistently found that for any given genome region, humans and chimps share at least 98 percent of their DNA. How could one to two percent of our genome differences be responsible for how we became human? Advances in bioinformatics and genomics are allowing scientists to make molecular comparisons among primate genomes and zoom in on precisely what makes us human. Most recently, two independent groups of scientists are doing what had only been thought possible in science fiction movies — they’re planning on resurrecting Neandertal DNA by using new sequencing techniques that piece fragments of the nuclear genome together.

Although Neandertal DNA will quantitatively assist in teasing out the 35 million base pair differences between chimp and man, it will be more difficult to make a concrete connection between candidate genes that are identified and any sort of human-specific phenotypic trait. The bottom line is that we don’t know what these candidate genes do and because of ethical reasons we can’t experimentally knock out these genes in humans to identify their function.

Take brain evolution, for example; there are more than 20,000 genes that could have helped shape the human brain. And the tests that involve identifying the crucial ones are based on seeing what sequences of DNA appear to mutate more quickly than the background rate of evolution. I have a hard time being convinced which of these apparently rapidly changing genes are important for hominid evolution. Thus, the challenge does not come from identifying these genes but in linking the evidence of positive selection to a notable function. Despite the genetic hyping that is often proclaimed in the popular media, there have been 10 genes in the past four years that have been suggested to have been key to brain evolution, obtaining more than this suggestive evidence based on rapidly varying DNA sequences doesn’t seem like it’s going to change soon, although someday we might be able to insert human and Neandertal DNA segments into mice to see what kinds of consequences it has. Likewise, theoretically, we could also obtain female volunteers to become surrogate mothers to host human eggs containing Neandertal DNA. But based on the opposition that human cloning has received, this type of research isn’t likely to be conducted anytime soon.

So far, testing out our genetic differences has mostly been attributed to luck. FOXP2 is the first gene shown to be necessary for the ability to develop speech and language. The gene would not have been identified had it not been for the opportune finding of a family in which about half of the members have a point mutation in the FOXP2 gene and also display pronounced verbal and oral dyspraxia. Only then were scientists able to zero in on one possible genetic component to the capacity to develop language, which had long been thought to be too mechanistically complex.

I think it’s an exciting time to be a genetic anthropologist. Preliminarily, much of comparative primate genomics is in its infancy and the quest for the genetic basis of human-specific traits has great potential. With more luck and better methodologies linking human genes to functions, scientists might be able to reveal what unique mutations actually make us human.

_Lenore is a junior. You can reach her at lpipes1@swarthmore.edu. _

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