Is it possible to infer the ancestral demography of a species from genetic data, based on its current genetic composition? "Yes," answers Jérôme Goudet, SIB Group Leader and associate professor in Population Genetics at the Department of Ecology and Evolution of the University of Lausanne. "If you consider a given species' genetic variants, their frequencies all have something to say about the species' past. An excess of rare variants, for example, is a signature of population expansion. A high genetic diversity is an indicator that a given population has been established over a long period." The hard part, though, is quantifying the data.

To address this, Jérôme Goudet and his lab put two species to the test: today's barn owl and humans. The current frequencies of barn owl and human genetic variants were quantified using Approximate Bayesian Computation (ABC). The results were then fed into quantiNEMO, a genetically-explicit stochastic simulation program specifically developed by Goudet's lab, to perform demographic simulations. Goudet shows that observations made on the demography of present-day barn owl and humans matched, satisfactorily, the simulations inferred by quantiNEMO.

"Besides understanding the past, such methods can also help to clarify the present-day distribution of genetic factors in a given species," says Jérôme. "As an example, he continues, this work has given us a greater understanding of the polymorphism observed in today's barn owl. As for humans, our research has shown that changes do not always occur under pressure but also merely by chance - thus countering the too popular notion that if a variant exists, it must be there for a reason."

Jérôme Goudet studied biology and agronomy at the Institut national agronomique in Paris. He then moved on to earn his PhD in 1993, at the University of Wales (UK) where he studied the genetics of geographically structured populations. He pursued his career at the Institute of Ecology in Lausanne, the Genetic and Biometry Laboratory in Geneva and the Department of Ecology & Evolution at Lausanne University, where he is currently associate professor in Population Genetics, and Head of the master program Behaviour, Evolution, Conservation.

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