Human Evolution At The Crossroads: Integrating Genetics And Paleontology

Using her own research on the teeth of baboons as a case in point, Leslea J. Hlusko said that some of the traits considered important to human evolution, such as the thickness of molar enamel, may be too simplistically interpreted by some paleontologists.

Hlusko organized a Monday symposium on human evolution at the annual meeting of the American Association for the Advancement of Science. She brought together experts who study phylogenetics, ancient DNA, developmental genetics, quantitative genetics and primate evolution so that they could share the same stage to discuss their current work, and where they may be able to go on together in an effort to understand the evolution of our ancestors. The session was discussed Sunday at a news briefing.

Hlusko's call for an integration of paleontology and genetics is also the focus of a perspective article that will appear online Monday ahead of print publication by the Proceedings of the National Academy of Sciences.

"Data from developmental genetics and biomedicine, coupled with advances in computer technology, now provide us with a wealth of new information from which to better understand the genetic and non-genetic influences underlying primate, including human, evolution," Hlusko said in an interview. "By combining these different data sets with the fossil record, we don't have to be just paleontologists, or just geneticists. Because selection operates on the genome through our anatomies, it makes better sense to conduct our research with a similarly integrative approach. Recent advances in genetics have now made this method more feasible for primate studies."

Research on early hominids, she argues, has benefited from an abundance of new fossil finds, but the emerging data are leading to competing interpretations of human origins and evolution instead of providing clarity. Research that integrates paleontology and genetics may provide some resolution to these debates, she said.

As an example, her recent study of teeth in more than 400 savanna baboons housed at the Southwest Foundation in San Antonio shows that, contrary to long-held assumptions, enamel thickness varies widely within a population. She and her colleagues also found that the underlying genetic architecture may have enabled rapid evolutionary changes in enamel thicknesses that could reflect changes in dietary habits over time.

The study, published online ahead of print by the American Journal of Physical Anthropology, is the largest genetic analysis of primate enamel thickness done so far.

"People have assumed that it is hard to change certain traits -- that if an organism has evolved thick enamel, its descendents cannot easily go back to thin enamel," she said. "The thinking has been that if hominid fossils 5 million years old have thick enamel, they are human ancestors. If they have thinner enamel, they must be chimpanzees."

That assumption, Hlusko said, "may be over simplified." Using their baboon study, Hlusko and colleagues argue that "when used uncritically, enamel thickness has the potential to confound rather than to clarify phylogenetic studies of higher primates."

The Monday morning AAAS session reflects a desire to "see integrative paleontological and genetic approaches as the norm rather than the exception in primate and human evolutionary studies," Hlusko said at a news briefing on Sunday. This integrative approach was first developed by scientists working outside the study of primates, such as Rudolf Raff of Indiana University, also a participant in the AAAS symposium. One of the goals for the symposium and Hlusko's PNAS article is to highlight the application of integrative biology to human evolutionary studies.

"Although many of the scientists currently involved in this integrative approach are united by their common interest in human evolution, I've realized over the last few years that many of us sometimes seem to speak different languages," she said.

"We often think about genetics and evolution from very different perspectives," Hlusko continued. "These conceptual divides lead to a bit of isolation and separation, and are actually holding back progress in both research and training. This symposium will give us an opportunity to come together and talk across our differences."

The true advancement in the understanding of human evolution will come primarily from two sources, Hlusko said: recovery of new fossils (fieldwork); and the integration between genetics, development and paleontology.

Speakers in the symposium who discussed their current research, in addition to Hlusko, a paleontologist incorporating quantitative genetic approaches, were Alan Walker of Pennsylvania State University, a primate paleontologist who discussed efforts to understand contradictory paleontological and genetic phylogenies; Chi-hua Chiu of Rutgers University, who gave a developmental genetics perspective on human evolution; and Hendrik Poinar of McMaster University in Canada, who studies the molecular components extracted from ancient fossils (ancient DNA).

Speaking in more general terms about the current state of integrated hominid paleontological/genetics research and where it may be headed were Kenneth M. Weiss of Pennsylvania State University, a developmental geneticist, and Raff, the author of the 1996 book "The Shape of Life: Genes, Development and the Evolution of Animal Form" and founder of "EvoDevo" (evolutionary-developmental biology).