Are Big Brains Smarter?

Are Big Brains Smarter?

 

Jeanna Bryner
LiveScience Staff Writer
LiveScience.com
Fri Apr 18, 9:55 AM ET

 

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. Not the case.

 


  1. seb

    The fact that so much of the brain is occupied by the association cortices raises a fundamental question: does more of it provide individuals with greater cognitive ability? Humans and other animals obviously vary in their talents and predispositions for a wide range of cognitive behaviors. Does a particular talent imply a greater amount of neural space in the service of that function?

    Historically, the most popular approach to the issue of brain size and behavior in humans has been to relate the overall size of the brain to a broad index of performance, conventionally measured in humans by “intelligence” tests. This way of studying the relationship between brain and behavior has caused considerable trouble. In general terms, the idea that the size of brains from different species reflects intelligence represents a simple and apparently valid idea (see figure). The ratio of brain weight to body weight for fish is 1:5000; for reptiles it is about 1:1500; for birds, 1:220; for most mammals, 1:180, and for humans, 1:50. If intelligence is defined as the full spectrum of cognitive performance, surely no one would dispute that a human is more intelligent than a mouse, or that this difference is explained in part by the 3000-fold difference in the size of the brains of these species. Does it follow, however, that relatively small differences in the size of the brain among related species, strains, genders, or individuals—which often persist even after correcting for differences in body size—are also a valid measure of cognitive abilities? Certainly no issue in neuroscience has provoked a more heated debate than the notion that alleged differences in brain size among races—or the demonstrable differences in brain size between men and women—reflect differences in performance. The passion attending this controversy has been generated not only by the scientific issues involved, but also by the spectre of racism or misogyny.

    Nineteenth-century enthusiasm for brain size as a simple measure of human performance was championed by some remarkably astute scientists (including Darwin’s cousin Francis Galton and the French neurologist Paul Broca), as well as others whose motives and methods are now suspect (see Gould, 1978, 1981 for a fascinating and authoritative commentary). Broca, one of the great neurologists of his day and a gifted observer, not only thought that brain size reflected intelligence, but was of the opinion (as was just about every other nineteenth-century male scientist) that white European males had larger and better-developed brains than anyone else. Based on what was known about the human brain in the late nineteenth century, it was perhaps reasonable for Broca to consider it an organ, like the liver or the lung, having a largely homogeneous function. Ironically, it was Broca himself who laid the groundwork for the modern view that the brain is a heterogeneous collection of highly interconnected but functionally discrete systems. Nonetheless, the simplistic nineteenth-century approach to brain size and intelligence has persisted in some quarters well beyond its time.

    There are at least two reasons why measures such as brain weight or cranial capacity are not easily interpretable indices of intelligence, even though small observed differences may be statistically valid. First is the obvious difficulty of defining and accurately measuring intelligence among animals, particularly among humans with different educational and cultural backgrounds. Second is the functional diversity and connectional complexity of the brain. Imagine assessing the relationship between body size and athletic ability, which might be considered the somatic analogue of intelligence. Body weight, or any other global measure of somatic phenotype, would be a woefully inadequate index of athletic ability. Although the evidence would presumably indicate that bigger is better in the context of sumo wrestling or basketball, more subtle somatic features would no doubt be correlated with extraordinary ability in Ping Pong, gymnastics, or figure skating. The diversity of somatic function vis-à-vis athletic ability confounds the interpretation of any simple measure such as body size.

    The implications of this analogy for the brain are straightforward. Any program that seeks to relate brain weight, cranial capacity, or some other measure of overall brain size to individual performance ignores the reality of the brain’s functional diversity. Thus, quite apart from the political or ethical probity of attempts to measure “intelligence” by brain size, by the yardstick of modern neuroscience (or simple common sense), this approach will inevitably generate more heat than light. A more rational approach to the issue, which has become feasible in the last few years, is to relate the size of measurable regions of known function (the primary visual cortex, for example) to the corresponding functions (visual performance), as well as to cellular features such as synaptic density and dendritic arborization. These correlations have greater promise for functional validity, and less pretense of judgment and discrimination




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