In brain evolution, size matters—most of the time

In brain evolution, size matters -- most of the time
An African sedge warbler, a species with a simple song that is also adapted to eating insects. Credit: Jordan Moore

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 size accounts for most of these differences, with larger brains leading to greater capabilities.

The study of 58 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 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 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.

"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.

Explore further

Size matters: Length of songbirds' playlists linked to brain region proportions

More information: Concerted and mosaic evolution of functional modules in songbird brains, Proceedings of the Royal Society B, rspb.royalsocietypublishing.or … .1098/rspb.2017.0469
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May 10, 2017
"...we may have first evolved larger brains, which then allowed for adaptations that enhanced brain regions that control specific abilities, such as language."

- We didn't evolve. We're domesticated. You wouldn't say that dogs evolved from wolves.

Our brains began to grow in response to technology. Tech gave us the ability to systematically eliminate the attritive elements in our environment. The result was chronic overgrowth.

Overgrowth made tribalism the norm, and conflict among tribes began to select for tribes whose members were better at foregoing their natural tendencies for self-preservation and repro rights in favor of tribal unity and cooperation.

Tribes with more internal turmoil and distrust were then overcome by tribes whose members were better at communicating, cooperating, planning, and remembering complex strategies. Our brains continued to grow.

This explains the delicate, unwieldy, defect-prone, and energy-hungry brains we are plagued with today.

May 10, 2017
And this is certainly not my idea.

"There can be no doubt that a tribe including many members who, from possessing in a high degree the spirit of patriotism, fidelity, obedience, courage, and sympathy, were always ready to give aid to each other and to sacrifice themselves for the common good, would be victorious over most other tribes; and this would be natural selection" (Darwin, 1871)

-And many others, as the link shows. Many, including Darwin and Dawkins, have trouble with this unique form of group selection, even though it explains so very much.

The trouble with academes is they cannot acknowledge a theory that leads to the heinous conclusions stemming from the tribal dynamic, that being defined as internal amity in conjunction with external enmity.

The conclusion for instance that bigotry is normal, that the dynamic is the source of morality, or that war has always been inevitable.

May 10, 2017
The weakness of this conclusion is that humans with brains the size of chimp's brains, due to microcephaly, none the less have language capabilities far beyond those of chimps not just in vocabulary but in the way they can process information, the way they can interact socially and so on.

This indicates that even with far less brain matter, it is the nature of the brain structure in humans that plays a strident role in the difference between human and non-human.

Once again the desire for simplistic answers to complicated questions has resulted in ridiculous conclusions. An adversarial approach to research where one camp is right and the other wrong significantly delays progress where both sides actually contribute to the overall outcome.

May 10, 2017
If you add the entire nervous system into the definition of "brain" you would be much closer to getting rational results.

Out bodies are our souls, our minds are just a virtual construct.

May 11, 2017
Once again the desire for simplistic answers to complicated questions
Your one example and sweeping conclusion are pretty simplistic yes? Can you provide test results that say those brains are equivalent to normal brains?

The pro who did the paper knows all about the theory you describe while putting much professional time and effort into his.

May 13, 2017
Microcephaly brains ARE NOT equivalent to normal brains and I said nothing of this sort, but they are also nothing like chimp brains even though they can be of the same size.

There are numerous papers describing the shortcomings of chimp brains and their inability to comprehend a number of abstract concepts that humans, including those with microcephaly, though to a diminished extent, can achieve. I have discussed this with Sue Savage Rumbaugh, Duane Rumbaugh and Frans de Waal, all members of a discussion group I run and there is no doubt in the truth of this observation.

I note that, while my comments were directed to the article above, the paper is nowhere near as one sided and far more professional saying that both brain size and structure are contributors which is what I said in my earlier comment, so I assume that the professional you mention would be equally as annoyed with the article's implication as I was...

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