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Can a Bigger Brain Be Engineered?

Part 3: Yes, but it doesn’t necessarily make an organism smarter.

Key points

  • Research suggests greater intelligence comes from our experience of a changing world and our ability to adapt to it.
  • One study showed fish that experienced a changing world performed substantially better on cognitive tasks than those reared on constant ration.
  • If a young organism can be flexible when faced with new conditions around them, they may achieve higher cognitive abilities as adults.

In Parts 1 and 2 of this series on brain size and intelligence, I discussed how brain size on its own tells us little about intelligence and behavioral complexity both within and across species, and I pointed out that human brains have, in fact, been shrinking over the past 30,000 years.

But you could object to these arguments by pointing out that they are retrospective: the evidence I cited compares brains from the past and in different species. In other words, the relevant data are not from experiments in a strict sense, where a scientist interacts directly with the system under study—the brain in this case—and manipulates it somehow.

Scientifically, we would like to perform an experiment where we can engineer bigger brains and measure performance on cognitive tests for manipulated individuals compared to control brains that have not been manipulated, or compared to individuals engineered to have smaller brains.

Source: Thiszun/Pexels

We obviously can't (and shouldn't) do this in humans, but it has been achieved in other species. A series of experiments where fish are bred to have larger brains have been performed by evolutionary biologists Alexander Kotrschal, Niclas Kolm, and colleagues in Sweden and elsewhere.

These studies have produced curious results. In a 2013 study of guppies, selective breeding over just a few generations produces large-brained individuals with 5-10% more brain mass than those bred to have smaller brains. Do the lucky big-brained fish get smarter? To answer this question, we need to ask how we can tell if a guppy is smart.

One way is to train them to perform behavioral tasks for a reward. Specifically, the task the researchers used involves associating some sensory stimulus with a reward. The ability to learn to associate visual cues with outcomes is something that presumably requires smarts.

The researchers did this by dividing the tank into three sections. The fish were initially in the middle section and could see cards in the other two sections on opposite sides of the tank. The cards had either two or four symbols on them. They were trained to associate food with one of the cards by putting the food in only the side with that card over several trails. Then the fish were presented with just the cards and no food. At this point, the scientists measured how many times they swam toward the correct card. So how did the big and small-brained fish do?

There was an effect of brain size for females: the larger-brained individuals made substantially more correct choices than small-brained females. However, though the small-brained females had brains more than 1/3 bigger than the small-brained males, both groups performed the cognitive task with the same success.

Moreover, the small-brained males did just as well at associating the cards with receiving a reward compared to the males bred to have larger brains. So even substantial changes in brain size engendered in careful experiments have no consistent effects on cognitive ability, at least in simple learning tasks.

What about cognitive performance in more natural situations? One behavior that requires a degree of cognitive ability is finding mates, and animals are naturally motivated to do this. So in a later experiment, the researchers again bred big-brained male fish—up to 13% bigger—and tested their mate-finding abilities. They put male fish into plexiglass mazes, lured by virgin females. You might expect the bigger-brained males to finish the maze more quickly. But the small-brained males were, on average more than a minute faster to complete the maze on the first try than the big-brained males (although the group averages were not significantly different).

Over time, the big-brained males reached a faster average rate than the small-brained animals, but the difference was relatively small—only about 40 seconds difference on average. In any case, both groups had some guidance provided by a hand-drawn net that pushed them along.

So in these guppies, at least, males seem to benefit little, if at all, from having a bigger brain. Females might benefit, but we can't necessarily extrapolate this possible sex difference to humans since guppy males and females differ much more than human males and females (sexual dimorphism).

The authors conclude, cautiously, that there are “costs and benefits” to having a bigger brain. But another study by Kotrschal and evolutionary biologist Barbara Taborsky points to something potentially more important than brain size that can be usefully associated with intelligence: the environment we are surrounded by. The idea is that greater intelligence comes from our experience of a changing world and our ability to adapt to it. In other words, if an organism can be flexible and innovative when faced with new conditions around them, especially when they are young, they may achieve higher cognitive abilities as adults.

Kotrschal and Taborsky experimented with different species of fish species to support this notion. For a fish, feeding is a nearly constant activity and the behavior that their bodies are largely designed around (a comparative neurobiologist colleague memorably described fish as "an arrow with a mouth at the tip"). So manipulating the feeding environment is a big deal for a fish, more so than, say, changing aquarium furniture. The researchers raised fish either on a rigid feeding regimen or on a changeable regimen. They tested the fishes' cognitive abilities using an association test like the one used for the guppies. They found that the fish that experienced a changing world performed substantially better on the cognitive task than the fish reared on constant rations. This cognitive advantage lasted for a year afterward, once they had become adults.

These are, again, fish. But we can still possibly take a lesson from these findings: we should try to embrace flexibility. Seek out new situations and experiences and accept that change is inevitable, even if you don't seek it out. This is also the conclusion I draw in my book An Internet in Your Head, which compares our brain's functioning to the internet's message-passing architecture. As I have written in a previous post, our brains are always changing, and so is the internet. Both succeed because they are built to manage change gracefully. This idea can help us understand fish intelligence and is perhaps even more salient for us humans.

So instead of engineering a bigger brain to become more intelligent, we may be better off performing "surgery" on our environment to make it more varied and diverse.

Copyright © 2021 Daniel Graham. Unauthorized reproduction of any content on this page is forbidden for reprint requests, email


Kotrschal, A., Corral-Lopez, A., Amcoff, M., & Kolm, N. (2015). A larger brain confers a benefit in a spatial mate search learning task in male guppies. Behavioral Ecology, 26(2), 527-532.

Kotrschal, A., Rogell, B., Bundsen, A., Svensson, B., Zajitschek, S., Immler, S., ... & Kolm, N. (2013). Experimental evidence for costs and benefits of evolving a larger brain. Current Biology, 23, 168-171.

Kotrschal, A., & Taborsky, B. (2010). Environmental change enhances cognitive abilities in fish. PLoS biology, 8(4), e1000351.