Yale Biologists Examine Long-Standing Genetics Mystery

Researchers discover several genes whose evolution appears to have been critical to the divergence of humans from their common ancestor with chimpanzees.

What makes humans different from chimpanzees? Evolutionary biologists from Howard University and the Yale School of Public Health have developed a unique genetic analysis technique that may provide important answers.

Michael C. Campbell, Ph.D., the paper’s first author and assistant professor in the Howard University Department of Biology, and co-author Jeffrey Townsend, Ph.D., the Elihu Associate Professor in Biostatistics at Yale, published their findings in the journal Molecular Biology and Evolution.

Their method—Model Averaged Site Selection via Poisson Random Field (MASS-PRF)—looks at protein-coding genes to identify genetic signatures of positive selection. These signatures are actually DNA changes that contribute to the development of beneficial traits, or human adaptations, that emerged during human evolutionary history and that are shared across the human species.

Other approaches have examined this question but analyses have focused on whole genes, typically missing focused evolution that often occurs in small regions of genes. The method Campbell and Townsend created identifies selection within genes, pinpointing sets of mutations that have undergone positive selection.

“It’s a quantum leap in our statistical power to detect selection in recently diverged species.”

Jeffrey Townsend

“Our method is a new way of looking for beneficial mutations that have become fixed or occur at 100 percent frequency in the human species,” Campbell said. “What we are concerned with are mutations within genes and traits that are specific to humans compared to closely related species, such as the chimpanzee. Essentially, we want to know is what are the mutations and traits that make us human and that unite us as a biological species.”

Townsend said the technique has far-reaching implications. It helped the research team discover several genes whose evolution appears to have been critical to the divergence of humans from their common ancestor with chimpanzees. The genes play roles in neurological processing, immunity, and reproduction, and the method could eventually help scientists identify many more. “It’s a quantum leap in our statistical power to detect selection in recently diverged species,” Townsend said.

Reference: “Detection of regional variation in selection intensity within protein-coding genes using DNA sequence polymorphism and divergence” by Zi-Ming Zhao, Michael C. Campbell, Ning Li, Daniel S.W. Lee, Zhang Zhang and Jeffrey P. Townsend, 28 July 2017, Molecular Biology and Evolution.
DOI:10.1093/molbev/msx213

Campbell began the research project with Drs. Zhao and Townsend while they were associate research scientists in the Department of Biostatistics at the Yale School of Public Health before he arrived at Howard University in 2015. Dr. Zhao, currently a research scientist at The Jackson Laboratory for Genomic Medicine, co-authored the paper.

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