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April 26, 2010

DETROIT- Large brains are uncommon in the animal kingdom and many of the species in which they appear - primates, elephants, dolphins - are far apart in lineage. A recent Wayne State study, however, suggests that for humans and elephants, the evolutionary path toward a large brain was very similar.


The study was made possible by the expanding set of publicly available genomes. "In the genome age that we're in, there's a great opportunity to elucidate the evolutionary steps that resulted in the origin of humans," Goodman said.



The analysis, which encompassed about 6,000 genes from each lineage, investigated the ratio of nonsynonymous mutations - which are indicative of adaptive evolution - to synonymous or "silent" mutations. They found that humans and elephants both have a high ratio of non-synonymous mutations in a set of genes known as aerobic energy metabolism (AEM) genes. AEM genes control the production of aerobic energy, a process that occurs in mitochondria.

One likely hypothesis for these similar adaptations - also known as convergent evolution - is that increased production of aerobic energy would satisfy the huge amount of energy that the large brains of elephants and humans require. "The study strengthens the evidence for the importance of these genes in the development of a large brain," Goodman said.

The next steps in this line of research will include the investigation of the specific nucleotide and protein replacements that comprised this genetic evolution. It also opens the door for similar genetic studies comparing humans to mammals of other lineages. "It will be very interesting to see if other large-brained, social mammals such as dolphins have the same adaptations in AEM genes," Goodman said. "These studies, among others, will further elucidate the genetic evolutionary mechanisms that resulted in characteristics that define us as humans and shaped the animal kingdom as we know it."

