Big Brains - Intelligence ?

Jeanna Bryner
LiveScience Staff Writer
LiveScience.com

If this were true, then perhaps big-headed people wouldn't be so pea-brained.

This question is mired in many unknowns. For one, scientists still debate over the definition of intelligence. For any IQ definition, how do you measure it? Further, do differences in IQ show up in daily life? And finally, does more brain tissue or a heftier brain equate with higher IQ?


One thing scientists do agree on: A big brain alone doesn't equate with smarts. If it did, elephants and sperm whales would win all the spelling bees. Rather, scientists look at brain mass relative to body mass in order to make any speculation about a creature's cognitive abilities.


So while an elephant noggin, at 10.5 pounds (4,780 grams), could squash a human think box in a purely physical battle of brains, you and I take the cake in a war of wits. Our brains, which weigh an average of 2.7 pounds (1,200 grams), account for about 2 percent of body weight, compared with an elephant's under one-tenth of a percent.


Studies have shown that across species relatively large brains "do seem to provide some complex cognitive skills, such as innovative solutions to ecological problems, more efficient resource mapping and food acquisition, and more complex social strategies (such as deception)," said Nancy Barrickman, a graduate student in Duke University's Department of Biological Anthropology and Anatomy.


Differences in brain size within a species, such as humans, are relatively small, making it difficult to tease out the effects of brain size and the effects of other factors. For instance, the difference in intelligence between an organism with, say, a brain that's 1,100 grams and one that's 1,400 grams (which could be found in humans) is confounded by other variables, including differences in density of neurons, other structural brain differences and socio-cultural factors.


And the debate continues ...


Brain size has nothing to do with scores on standardized intelligence tests, according to a brain-scan study of young children.


Michael McDaniel, an industrial and organizational psychologist at Virginia Commonwealth University, has claimed that bigger brains do make for smarter people. Many researchers, however, disagree with McDaniel's conclusion. His research, published in 2005 in the journal Intelligence, suggested that across all age and sex groups, brain volume is linked to intelligence.


Men are smarter than women, according to research published in 2006, which the study researchers say could be due to men having relatively larger brains, a difference of about 0.2 pounds (100 grams). Another scientist put forth several socio-cultural factors that would make the men-smarter results null.


Average brain weights for primates (not relative to body size):

Chimpanzee (Pan troglodytes) - 0.77 pounds (350 grams)
Mountain gorilla (Gorilla gorilla beringei) - 0.95 pounds (430 grams)
Mouse lemur (Microcebus murinus) - 0.004 pounds (2 grams)

Sizing up brains for the rest of the animal kingdom, would include:

Sperm whale - 17 pounds (7,800 grams)
Walrus - 2.4 pounds (1,100 grams)
Domestic cat - 0.06 pounds (30 grams)

If brain size had anything to do with innovation and creativity, some scientists expected to see a link between the so-called Mind's Big Bang (the emergence of bone tools and cave paintings that occurred between 50,000 and 70,000 years ago) and the emergence of modern-size human brains.