When Charles Darwin first sketched how species evolved by natural selection, he drew what looked like a tree. The diagram started at a central point with a common ancestor, then the lines spread apart as organisms evolved and separated into distinct species.
In the 175 years since, scientists have come to agree that Darwin's original drawing is a bit simplistic, given that multiple species mix and interbreed in ways he didn't consider possible (though you can't fault the guy for not getting the most important scientific theory of all time exactly right the first time). Using a tree-like structure is a great way to show the history of the evolution of a species, or its phylogeny. But it's not so great for showing the population history of groups within a single species, such as humans, who can move around and interbreed with each other.
Jonathan Pritchard, PhD, professor in the department of human genetics, studies the nature of these human genetic variations by combining methods from evolutionary biology and statistics. Intrigued by recent research on the Neanderthal genome that suggests more interbreeding with Homo sapiens than previously thought, Pritchard wanted to develop a general method for estimating gene flow between different groups within the same species over time. In a recent paper published in PLOS Genetics, he and Joseph Pickrell, a former University of Chicago researcher now at Harvard, described a software model they developed that can infer the history of population splits and mixtures within a species based on modern DNA.
"If you try to make a tree of population histories within a species, there's always the possibility that you've got genes flowing from one branch to another," Pritchard said. "The populations can interbreed, so if they're geographically together or if there's movement from one place to another, then this tree representation is not necessarily going to be a good way of representing history
|Contact: Matt Wood|
University of Chicago Medical Center