Expert: John Shea - 6/19/2003

Question
Hi Dr. Shea, I just stumbled onto this website and I think its fantastic that people like you help to make this resource available.  My question is this: how much of a correlation is there between brain size and intelligence?  In anthropology class, it was made to seem as if this was the most important factor in our success as a species.  But I can't help but think that surely there are animals alive today that have brains larger than ours (elephants, whales).  Why are they then not more intelligent than us?  What are your thoughts on this?  Thanks a lot.

Answer
Dear Jordan
Within Homo sapiens, there is no proven strong relationship between brain size and intelligence.  The strongest morphological correlates for intelligence involve soft-tissue neurological structure of the brain, the "wiring" if you will.  This quality is influenced jointly by genetics and behavior (learning).  As you might expect in a social species like ours, the reproductive consequences of relatively low intelligence are fairly severe (extinction), so there's probably not a lot of genetically-programmed variation in the neural structures underlying intelligence.  Most of the variation is probably a result of variation in learning.
Brain size differences between species have to be considered in terms of the size of the creatures being compared.  Most mammals have brain sizes more or less in proportion to their body sizes, except we modern humans, whose brains are somewhat large for our body size.
Among recent human ancestors, there is a long-term trend towards species with bigger brains, and this has been most plausibly connected to increases in social group size, and probably to dependence on language (to augment grooming behavior).  I'm not sure about intelligence/brain size as predictors of long-term evolutionary success. Evidence for complex intelligence is rare in the history of life on earth, and there are many successful mammal species (i.e., ones that lasted a long time in many different regions) that have relatively small brains.
If you want to read more about this, have a look at some of the recent books written by Robin Dunbar, e.g., Grooming, Gossip and Language, and Terence Deacon's The Symbolic Species.
Cheers,
John Shea