Science Covers the Sequencing of the Chimpanzee Genome
Tammy the chimpanzee. Photo by Carol Weerts, Saint Louis Zoo
The sequencing of the chimpanzee genome is covered in the 2 September 2005 issue of the journal Science and includes a report, an editorial, two "Perspectives" and a news story.
Evolution in Humans and Chimps
Using data from the soon-to-be published chimpanzee genome sequence, researchers have addressed the role that changes in genetic material over time played in the emergence of humans and chimpanzees from their common ancestor.
Svante Pääbo and colleagues compared the evolution of both gene expression patterns and the corresponding gene sequences in brain, heart, liver, kidney and testis of humans and chimpanzees. They found that gene sequences and their expression patterns evolve in a similar manner and that overall this evolution in humans and chimpanzees conforms to the "neutral theory" of molecular evolution.
According to this theory, a large portion of the genetic changes that occur during evolution have neither positive nor a negative effect, but they are passed along to future generations nonetheless, through a process called "genetic drift." Genes on the X-chromosome that are expressed in testes, however, showed evidence of "positive selection." In this scenario, new variants of genes appear to have conferred advantages on both human and chimp ancestors.
Although genes expressed in the brain have changed less than genes expressed in other analyzed tissues, the researchers found that genes active in brain have accumulated more changes on the human than the chimpanzee lineage, suggesting a special role for the brain during human evolution.
The Future of Great Ape Research
The chimpanzee genome has the potential to help answer the question "what makes us human," but this understanding will also require more information about what it's like to be a great ape. The pair of "Perspectives" looks at the knowledge we've gained thus far from studying chimpanzees and other great apes and highlights the need for conserving these species.
Edwin McConkey and Ajit Varki describe some of the lines of research that will be necessary to complement our understanding of the chimp genome itself. These include sequencing other primate genomes and comparing human gene expression with that of other primates. These efforts must take into account ethical considerations, the authors say, since it is unacceptable to sacrifice a great ape simply to obtain tissue samples. Thus, there is a need for a network of great ape keepers, such as sanctuaries and zoos, to make tissue samples available from great apes that die of natural causes or must be euthanized because of incurable suffering. The authors also foresee research using great ape genes in transgenic mice, the possible creation of stem cell lines from ape embryos under ethically acceptable circumstances, and studies that lead to better care for great apes.
In a second "Perspective," Marc Hauser reflects on his experiences observing great apes, what researchers have learned about chimpanzees from studying them in the wild, and the danger that there may soon be no individuals left to study. Alison Jolly echoes these sentiments in an editorial, noting that "All the great apes of the world together number less than the human population of Brighton, England; the most numerous species less than the people of Abilene, Texas."
Daniel B. Kane and Kathy Wren
31 August 2005