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Paper Sets Framework For Exploring Evolution Of Species

In 1999, a seminal article put forward a new framework for exploring the evolution of species. The paper was by Dr. Sergey Gavrilets, Associate Professor of Ecology & Evolutionary Biology and Mathematics at the University of Tennessee.

On June 30 of this year, the American Society of Naturalists (ASN) honored Dr. Gavrilets with the Presidential Award for that article, the best paper published in The American Naturalist in 1999.

"It is very helpful to have a simple model when trying to understand a complex phenomenon such as biological evolution," said Gavrilets. "We can start by looking at the relationships between an organism's sequence of genes -- its genotype -- and the probability of that organism surviving until reproductive age -- its fitness."

In 1932, Sewall Wright, one of the founders of modern evolutionary biology, introduced the concept of using a three-dimensional geographic landscape as a metaphor for the complex interactions between genotype and fitness.

Following Wright, these landscapes have usually been imagined as "rugged" surfaces composed of "adaptive peaks" separated by "adaptive valleys." Peaks are different species, the valleys between, unfit hybrids. A new species is created when a population shifts from one peak to another, crossing an adaptive valley.

In his award-winning paper, Gavrilets describes a new approach to modeling speciation, one that more fully addresses genetic complexity.

"The analogies coming from our three-dimensional world are not necessarily good for biological evolution," said Gavrilets. "Even bacteria have over a thousand genes with over a million base pairs. Looking at the possible variation among individuals, this means that the dimensionality of adaptive landscapes is really on the order of thousands (or millions) rather than the three of our world."

Within the highly dimensional space formed from all possible combinations of genes, genotypes with high fitness tend to form networks rather than peaks. These networks can be visualized as ridges that populations can explore without ever having to cross an adaptive valley. Among the ridges are holes that represent genotypes with low fitness, those that will probably not reproduce successfully. Viewed from the three-dimensional world, the resulting "holey adaptive landscape" is a flat surface with many holes.

"In the new metaphor, microevolution can be viewed as the climbing of a population from a 'hole' towards the holey adaptive landscape, and macroevolution can be viewed as the movement of the population along the holey landscape," said Gavrilets. "New species are formed when diverging populations come to be on opposite sides of a hole."

Funding from the National Institutes of Health (NIH) supports Gavrilets' research on new approaches to modeling speciation. The American Naturalist article and others are available in PDF format from Gavrilets' website.

[Contact: Dr. Sergey Gavrilets, Zoe Hoyle]






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