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New wrinkle in tale of wolf-to-dog evolution
By analyzing MRI scans of the foxes, Hecht and her colleagues showed that both the foxes bred to be tame and those bred to be aggressive have larger brains and more gray matter than those of the control group. These findings run contrary to other studies on chickens, sheep, cats, dogs, horses, and other animals that have shown domesticated species have smaller brains, with less gray matter, than their wild forebears.
Hecht and her team of researchers from Harvard, University of Illinois at Urbana-Champaign, Emory University, Cornell University, and the Russian Institute of Cytology and Genetics say they can’t be sure why this happens without further study. Their leading hypothesis centers on how the tame and aggressive strains have both been bred for specific behaviors at an accelerated time frame compared with many other domesticated animals. Dogs, for example, have been domesticated for at least 15,000 years.
“Both the tame and aggressive strains have been subject to intense, sustained selection on behavior, while the conventional strain undergoes no such intentional selection,” they wrote. “Thus, it is possible that fast evolution of behavior, at least initially, may generally proceed via increases in gray matter.”
As they analyzed the MRI scans, scientists noticed another surprise: similarities in the ways that the brains of the aggressive and tame foxes were changing. Both, for instance, showed enlargement in many of the same regions, including the prefrontal cortex, the amygdala, the hippocampus, and the cerebellum.
Results suggest that selection for opposite behavioral responses can produce similar changes in brain anatomy. It also appears that significant shifts in the structure and organization of the nervous system can evolve very quickly. In fact, it can happen within the span of less than 100 generations.
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