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5 December 2013 11:26 am ,
Vol. 342 ,
Dyslexia, a learning disability that hinders reading, hasn't been associated with deficits in vision, hearing, or...
Exotic, elusive, and dangerous, snakes have fascinated humankind for millennia. They can be hard to find, yet their...
Researchers have sequenced and analyzed the first two snake genomes, which represent two evolutionary extremes. The...
Snake venoms are remarkably complex mixtures that can stun or kill prey within minutes. But more and more researchers...
At age 30, Dutch biologist Freek Vonk has built up a respectable career as a snake scientist. But in his home country,...
Since arriving on the island of Guam in the 1940s, the brown tree snake ( Boiga irregularis ) has extirpated native...
An animal rights group known as the Nonhuman Rights Project filed lawsuits in three New York courts this week in an...
Researchers have been hot on the trail of the elusive Denisovans, a type of ancient human known only by their DNA and...
- 5 December 2013 11:26 am , Vol. 342 , #6163
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Chimps Are Champs of Genetic Changes
16 April 2007 (All day)
Whose genome has evolved more, chimpanzee or human? You might answer "human.” After all, with our nearly hairless skin and larger brains, it would surely seem that genetically we've outpaced our closest relatives since parting company 7 million years ago. But that anthropocentric view is mistaken, according to a new study by researchers from the University of Michigan, Ann Arbor.
The team was searching for genetic evidence of adaptive changes. These mutations are positively selected; that is, they confer a benefit that makes survival and reproduction more likely and have spread throughout a population via natural selection. Jianzhi Zhang, a population geneticist, and his colleagues compared nearly 14,000 protein-coding genes in humans and chimpanzees, which have about the same size genome. Using a statistical analysis, they identified 154 human genes that have been positively selected. In contrast, they found 233 such genes in chimpanzees, a 51% increase, they report online this week in the Proceedings of the National Academy of Sciences.
What explains that discrepancy? The chimpanzees' larger past population, says Zhang. Other genetic data have shown that the human population remained smaller than that of the chimpanzee for most of the last 1 million to 2 million years, he notes, and as population genetic theory predicts, recombination will produce more adaptive genetic changes in larger groups.
Intriguingly, the fast-evolving genes in humans and chimpanzees do not readily account for the obvious physical differences between the two species, Zhang points out. In the chimp, genes that have outpaced those in humans include ones involved in protein metabolism, gene transcription, and stress response. "You wouldn't immediately notice if the chimpanzee has a better stress response than a human," says Zhang. In the human, too, the differences appear to be subtle, with selection working rapidly on genes concerned with fatty acid metabolism and phosphate transport.
The study "challenges the idea that there was a great burst of adaptive change in humans, one that was more profound than in other primates or mammals," says Morris Goodman, an evolutionary biologist at Wayne State University School of Medicine in Detroit, Michigan.
But that's not the whole story, argues Ajit Varki, a physician-scientist at the University of California, San Diego. "It's a terrific paper, but they're only looking at one mechanism, the changing amino acids in proteins. Other mechanisms in gene evolution--such as gene expression, duplication, conversion, and inactivation--are likely to be equally important." Further, Varki adds, these types of genomewide analyses are limited, because they do not address the issue of gene function. "It could be that the deletion of a specific gene or a single amino acid change could have more biological significance than a large number of genes that seem to have undergone many changes." And that means we're still a long way from explaining what makes us human--or them chimpanzee, he says.