Brain parts evolve independently: Study

The brain, the body’s most powerful organ, is not a single uniform entity but has parts that can evolve independently of one another, a new study says.

The unique 15-year study, based on compelling evidence unearthed by researchers from the universities of Tennessee and Manchester, as also the Harvard Medical School, also identified several genetic loci (the position of a gene on chromosome) that control the size of different brain parts.

They were tasked with finding out whether if different parts of the brain can respond independently of one another to evolutionary stimulus (individual evolution) or whether the brain responds as a whole (concerted evolution), the journal Nature Communications reported.

Unlike previous studies, researchers compared the brain measurements within just one species, involving about 10,000 mice. Seven individual parts of each brain were measured by volume and weight.

The entire genome, except the Y chromosome, was scanned for each animal and the gene set for each brain part identified, according to a Machester statement.

Reinmar Hager, evolutionary biologist from Manchester, who compared variation in the size of the brain parts to variation in the genes, found that the variation in the size of brain parts is controlled by the specific gene set for that brain part and not a shared set of genes.

He also compared the measurements for each mouse to the overall size of its brain. Surprisingly he found very little correlation between the sizes of the brain parts and the overall size of the brain.

Hager said: “If all the different brain parts evolved as a whole we would expect that the same set of genes influences size in all parts.

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“However, we found many gene variations for each different part of the brain supporting a mosaic scenario of brain evolution.

“We also found very little correlation between the size of the brain parts and the overall size of the brain. This again supports the mosaic evolutionary hypothesis,” concluded Hager.

Using the data collected from the mice Hager and colleagues found evidence that the size of the brain is governed by an independent gene set to the one that controls the size of the body.

Genetic architecture supports mosaic brain evolution and independent brain–body size regulation, Reinmar Hager, Lu Lu, Glenn D. Rosen & Robert W. Williams, Nature Communications 3, Article number: 1079 doi:10.1038/ncomms2086

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