The Search for the Genetic Basis of Human Uniqueness

Dr. Caro-Beth Stewart

Associate Professor, Biology, SUNY Albany

This is the recap of a talk given at the Nov 9, 2003 CDHS monthly meeting.

Caro-Beth Stewart, Associate Professor, Biology, SUNY Albany, spoke with us at the November meeting on "The Search for the Genetic Basis of Human Uniqueness." The discussion covered a lot of ground, including the history of the human genome project and the 1.5% genetic difference between humans and chimps. Also discussed, was the attitude of the U.S. medical establishment to evolutionary research (it has a tendency to dismiss its value). Professor Stewart then reviewed evolution research as it relates to the study of AIDS, and also the different approaches involved in researching genomic evolution.

Some definitions of evolution:

1. Descent with modification – Charles Darwin.

2. Change over time (a better definition is: heritable change over time)

3. E=M ÍF (evolution = mutation Í fixation) Evolution is the product of mutation and fixation. Mutation is the alteration of the nucleotide sequence of DNA in an organism. Fixation is when a mutation spreads to 100% of the individuals in a species or population.

Professor Stewart pointed out that there is only a 1.5% difference between humans and chimpanzees at the genetic level. There is a similar percentage of difference found between different species of flies or different species of sea urchins. The big question, of course, is what are the genetic changes that make us uniquely human? Stewart says it is those that were fixed on the lineage leading from the common ancestor of humans and chimpanzees to the common ancestor of modern humans.

Stewart's research covers a wide range of primate anatomical parts from stomachs to testicles to sperm DNA. It is increasingly awkward for her husband to explain her work to others, which he describes as covering the ground "from guts to nuts." In amongst the complex charts and graphs of the presentation, there was the occasional startling example of the large size of chimp and bonobo testicles in relation to other primates. Stewart says that a common question has been to ask why humans evolved to be so monogamous. But a better question, she says, is why have chimps and bonobos evolved to be so promiscuous (monogamous primates include humans, gorillas, orangutans – and Stewart says gibbons are so monogamous they make humans look like sluts!).

This question, and the many others that biologists are asking, are researched by utilizing a comparative genomic strategy. Stewart described two comparative genomic strategies. One is to search for similarities between distant relatives to identify the conserved functions. The other (and this is the one that Stewart uses in her research) is the search for differences between close relatives to identify the evolved functions. The talk then concluded with an intense question and answer session.

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