Big Brains Strike Again
Two back-to-back studies on how big-brained animals thrive in new habitats piqued my curiosity about the real implications of relative brain size.
If you heard last week’s podcast, you know that species with big brains relative to their bodies are more successful than small-brained ones in new habitats. That holds for birds, mammals, amphibians, and reptiles—all of which often land in unfamiliar environments due to human trade and travel.
Now another study finds that a big brain-to-body ratio helps birds thrive in cities. Among 82 songbird species in France and Switzerland, birds such as magpies that flourish in urban centers are bigger-brained than birds like wood warblers that avoid cities.
In a sense, moving to a city is much like moving to a habitat on the other side of the planet. Both require a species to discover new foods, avoid new predators, and cope with different physical surroundings than those with which it evolved.
But how does a big brain help an animal meet such challenges? Certainly, dozens upon dozens of studies link relatively large brains to complex traits such as social group size and innovation (creating new tools and new foods). The authors of the newest studies suggest that it’s this behavioral flexibility that also confers success in new environments.
That may be logical, but behavioral biologist Sue Healy finds the argument frustrating. She’s at the University of St. Andrews in the U.K. In 2007, Healy co-authored a paper that essentially said, enough already with the brain size correlations! These studies tend to treat the brain as a black box. Rarely does anyone know which specific brain areas control a given trait—and individual brain areas are hard to measure. So, whole-brain volume stands in as a proxy.
It’s also unclear which of the many traits linked to big brains are also correlated to one another, and none of the correlations clearly imply causation. In other words, things are a bit murky.
At the very least, Healy would like to see all the brain-related traits—from bonding with a mate to using unpredictable habitats—go into one big statistical analysis to tease out the most important ones for future study. Ideally, that would be followed by experiments that show in greater detail which brain areas vary in size with those traits.
In the meantime, whole-brain volume serves as a black box proxy for… something, or maybe for different things in different species. Clearly, big brains can be helpful for certain things. Until the underlying biology is worked out, brain size can be duly noted as one predictor of how a species may fare in the face of urbanization, climate change, or introduction to a new habitat.
But it’s frustrating to rely on proxies instead of detailed experiments. Perhaps we ourselves need still bigger brains to figure it out.
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