Building bigger dolphin brains

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Ed Yong reports on a new study demonstrating a history of positive selection on the gene ASPM in cetaceans. Bruce Lahn’s group previously showed that this gene has been positively selected in primate lineages, including recent humans: “Same gene involved in bigger brains of dolphins and primates”.

Now, Shixia Xu from Nanjing Normal University has found that a gene called ASPM played an important role in the evolution of cetacean brains. The gene shows clear signatures of adaptive change at two points in history, when the brains of some cetaceans ballooned in size. But ASPM has also been linked to the evolution of bigger brains in another branch of the mammal family tree ours. It went through similar bursts of accelerated evolution in the great apes, and especially in our own ancestors after they split away from chimpanzees.
It seems likely that both primates and cetaceansthe intellectual heavyweights of the animal worldboth owe our bulging brains to changes in the same gene. Its a significant result, says Michael McGowen, who studies the genetic evolution of whales at Wayne State University. The work on ASPM shows clear evidence of adaptive evolution, and adds to the growing evidence of convergence between primates and cetaceans from a molecular perspective.

Molecular mechanisms of convergence have proved to be very common in the evolution of different mammalian orders. Mechanistically, evolution seems to select the same pathways when the same general functional requirements are adaptive. It is interesting that cetaceans and primates have broadly similar social and communication constraints, but very different ecological constraints in other respects, such as diet, thermoregulation navigation and home range.