While it may seem obvious, the hypothesis that big brains are an adaptation to novel environmental conditions has had relatively meager empirical support. This paper goes far to turn that around.
Today’s Research Review:
- Title: Big Brains, Enhanced Cognition, and Response of Birds to Novel Environments,
- Authors: Daniel Sol, Richard P. Duncan, Tim M. Blackburn, Phillip Cassey, and Louis Lefebvre.
- Date: 2005.
“The widely held hypothesis that enlarged brains have evolved as an adaptation to cope with novel or altered environmental conditions lacks firm empirical support. Here, we test this hypothesis for a major animal group (birds) by examining whether large-brained species show higher survival than small-brained species when introduced to nonnative locations. Using a global database documenting the outcome of > 600 introduction events, we confirm that avian species with larger brains, relative to their body mass, tend to be more successful at establishing themselves in novel environments. Moreover, we provide evidence that larger brains help birds respond to novel conditions by enhancing their innovation propensity rather than indirectly through noncognitive mechanisms. These findings provide strong evidence for the hypothesis that enlarged brains function, and hence may have evolved, to deal with changes in the environment.”
It looks like the big brain hypothesis, what they call the Brain Size-Environmental Change (BS-EC) hypothesis, has survived this test, helping to bolster our intuitions.
Notes & Quotes
“Theoretical models and empirical evidence suggest that large brains can process, integrate, and store more information about the social and physical environment, enhancing the propensity of individuals to modify or invent new behaviors in potentially adaptive ways. Particularly remarkable is the recent finding that brain size is positively associated with the ability for behavioral innovation and learning in birds and mammals. Despite this progress, it remains to be demonstrated what selective advantages large brains provide for the survival and or reproduction of animals in the wild.”
But this was the first time the adaptive hypothesis has been tested directly in a study of this size (so far as I know). They believed that “A strong test of the BS-EC hypothesis would require a direct measure of differential survival of species in an obvious situation where new environments are encountered and behavioral flexibility may make a life-or-death difference.”
“We used a previously compiled global database documenting all recorded human-mediated introductions of birds to new locations.”
This database included info on “196 species and 35 families”. Further,
“We considered an introduction to be successful if it resulted in the establishment of a persistent or probably persistent population in the recipient island or state, and unsuccessful otherwise (introductions described as possible successes were ignored).”
They got data about brain mass for over 1,967 species. They noted that, “Larger species tend to have larger brains, and this allometric effect needs to be accounted for before any comparison can properly be made.”
Their results suggest that:
“… birds with larger brains are better able to invade novel locations. This result also is supported by our analysis at the family level. At this taxonomic level, there is a significant positive relationship between relative brain size and invasion potential.”
They also looked at the cognition link and found that:
“… innovation propensity was positively related to relative brain size among avian families.”
Our findings support the hypothesis that large or elaborated brains function, and hence may have evolved, to deal with changes in the environment… Finally, the ‘‘positive feedback’’ hypothesis proposes that it is the tendency of large-brained animals to discover and explore novel conditions that expose them to changes in the environment. Yet, all these hypotheses are essentially based on the same principle, that enlarged brains enhance the cognitive skills necessary to respond to changes in the environment, and thus may be integrated into the more general BS-EC hypothesis. The selective pressure to deal with novel or altered circumstances may have been a powerful evolutionary force for increasing the size of the brain.”
Just because a hypothesis seems to be intuitively “obvious” does not mean that it is (e.g., the sun does not revolve around the earth). It’s worth checking. I wonder how mammals would hold up…
Now go lift something heavy,
PS. The photo at the top is of a Woodland Kingfisher.