( Humans and chimps share most of their g...)Less is more, gene study shows

Scientists would like to know how and when such differences arose, and new research from the University of Michigan shows how one process---gene loss---may have figured in.

The work, by a group led by associate professor of ecology and evolutionary biology Jianzhi Zhang, is reported in the Feb. 14 issue of the open-access journal PLoS Biology.

Researchers who speculate about human origins have come up with three main scenarios for how we ended up with our unique traits, Zhang said. The first possibility is that we acquired completely new genes that other apes don't have. Another is that some of our genes have taken on different functions through mutation.

It's also possible that we humans lost some genes along the way, and those losses provided opportunities for changes that otherwise could not have occurred. For example, scientists have shown that over the course of evolution, humans lost a gene that produces a particular jaw muscle protein. Perhaps the loss of that gene gave us smaller jaw muscles, making room in our skulls for bigger brains.

That's just speculation, and until now there was no concrete evidence for the "less is more hypothesis" that losing certain genes offered tangible benefits, Zhang said. "So we wanted to know how many genes have been lost and what kinds of genes have been lost in human evolution, and second, whether any of those gene losses was a good thing."

Zhang's group started by scrutinizing a database of human pseudogenes---stretches of DNA that look like known genes but don't function as genes. Then the researchers weeded out pseudogenes that never had been functional in any organism. From those that remained, they further narrowed the field to only those human pseudogenes that had working counterparts in
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Source:University of Michigan