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In Brain Evolution, Size Matters – Most of the Time

Summary: Study reveals we may have first evolved larger brains that allows for adaptions which enhanced brain regions controlling specific abilities.

Source: Cornell University.

Which came first, overall bigger brains or larger brain regions that control specialized behaviors? Neuroscientists have debated this question for decades, but a new Cornell University study settles the score.

The study reports that though vertebrate brains differ in size, composition and abilities, evolution of overall brain size accounts for most of these differences, with larger brains leading to greater capabilities.

The study of 58 species of songbirds also found that once a species evolved a larger brain, brain regions that control the beak and mouth, and the area for song, developed additional complex neural networks.

The paper, co-authored by Jordan Moore Ph.D., currently a postdoctoral fellow at Columbia University, and Timothy DeVoogd, a Cornell professor of psychology, was published May 10 in the Proceedings of the Royal Society B.

The findings suggest that this principle may also help explain human evolution; we may have first evolved larger brains, which then allowed for adaptations that enhanced brain regions that control specific abilities, such as language.

“Most neuroscientists believe there is nothing special about the way that our brains have evolved, that what we need to do is understand the principles that underlie brain evolution in general, which is what this study involves,” said DeVoogd. “The way you build a bigger brain is not just making everything bigger but rather slowing down or lengthening late pieces of development.”

In this way, bigger brains have a more developed cortex (which plays key roles in memory, attention, perception, awareness, thought, language and consciousness) that is the last region to develop in animals and humans.

The study is the first to compare — and resolve — two competing theories of brain evolution. One theory holds that natural selection drove progressive changes in particular areas of the brain, which then led to larger overall brains in species that needed them to survive.

The other theory contends that some species acquired a bigger brain in general, and its larger basic parts could then be recruited for specific complex behaviors.

To test these theories, Moore and DeVoogd measured the sizes of overall brains and 30 discrete areas that control behaviors in 58 songbirds spanning 20 families.

“One of the advantages of looking in the brains of birds is that it’s relatively easy to get samples from lots of different species, and there’s a lot of data on what the different species do. And specific areas devoted to these functions can be easily seen in the brain,” DeVoogd said.

Most of the variation in brain regions was accounted for by differences in the brain’s overall size. But in two specific systems there was a significant amount of variation beyond what could be explained by brain size. Areas that controlled song were much larger in species that produce more varied and complex songs. Also, brain areas controlling the face and mouth were especially large in species with short, fat beaks that eat seeds, and they were small in species with long, thin beaks that eat insects.

Image shows a drawing of a brain.

The findings suggest that this principle may also help explain human evolution; we may have first evolved larger brains, which then allowed for adaptations that enhanced brain regions that control specific abilities, such as language.NeuroscienceNews.com image is for illustrative purposes only.

“If you’ve ever watched a bird deal with a sunflower seed, it pushes the seed around with its tongue and grasps it with different points in its beak. And then it is able to break it open and get the inside out,” DeVoogd explained.

When it comes to humans, “it’s always been controversial how we got to be who we are,” DeVoogd said. Since supporting a big brain requires great demands on energy and oxygen, some researchers speculate that changes in the diets of early humans, including the ability to find and cook high-quality food, helped facilitate overall human brain growth by supplying the needed calories and protein.

Others speculate that living socially protected early humans and created evolutionary pressures for developing language, DeVoogd said.

About this neuroscience research article

Funding: The study was funded by the National Science Foundation, the Frank M. Chapman Memorial Fund, the American Ornithologists’ Union and the U.S.-Hungarian Joint Scientific Fund.

Source: Daryl Lovell – Cornell University
Image Source: NeuroscienceNews.com image is in the public domain.
Original Research: Abstract for “Concerted and mosaic evolution of functional modules in songbird brains” by Jordan M. Moore and Timothy J. DeVoogd in Proceedings of the Royal Society B. Published online May 10 2017 doi:10.1098/rspb.2017.0469

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Abstract

Concerted and mosaic evolution of functional modules in songbird brains

Vertebrate brains differ in overall size, composition and functional capacities, but the evolutionary processes linking these traits are unclear. Two leading models offer opposing views: the concerted model ascribes major dimensions of covariation in brain structures to developmental events, whereas the mosaic model relates divergent structures to functional capabilities. The models are often cast as incompatible, but they must be unified to explain how adaptive changes in brain structure arise from pre-existing architectures and developmental mechanisms. Here we show that variation in the sizes of discrete neural systems in songbirds, a species-rich group exhibiting diverse behavioural and ecological specializations, supports major elements of both models. In accordance with the concerted model, most variation in nucleus volumes is shared across functional domains and allometry is related to developmental sequence. Per the mosaic model, residual variation in nucleus volumes is correlated within functional systems and predicts specific behavioural capabilities. These comparisons indicate that oscine brains evolved primarily as a coordinated whole but also experienced significant, independent modifications to dedicated systems from specific selection pressures. Finally, patterns of covariation between species and brain areas hint at underlying developmental mechanisms.

“Concerted and mosaic evolution of functional modules in songbird brains” by Jordan M. Moore and Timothy J. DeVoogd in Proceedings of the Royal Society B. Published online May 10 2017 doi:10.1098/rspb.2017.0469

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