How smart is smart?
Is human intelligence still evolving?
EMBO reports (2009) 10 (11), 1198-1201
The development of higher cognitive functions in Homo sapiens—commonly and perhaps wrongly described as intelligence …
Bob Sternberg, for instance, a psychologist from Tufts University (Medford, MA, USA) and a pioneer of human intelligence research, believes that intelligence is an adaptive trait, but not a quantity that can be measured by standard intelligence quotient (IQ) tests. Instead, he has defined human intelligence as “a mental activity directed toward purposive adaptation to, selection, and shaping of real‐world environments relevant to one’s life” (Sternberg, 1985). However, there is a caveat to this so‐called ‘triarchic’ theory: its human devisers are not objective bystanders. “Higher levels of intelligence as we conceive of it can be and [have] been adaptive,” Sternberg said. “I say ‘as we conceive of it’ because the concept [of intelligence] is in large part a human invention of successful people to explain their own success.”
“For a neuroscientist, any aspect of ‘intelligent behaviour’ involves many different processes—attention, motivation, arousal, motor skills, perception, memory.
To lump all these together into one ‘crystallized intelligence’ makes no biological sense
A 2006 study from the University of Chicago (IL, USA) suggested that two genes, microcephalin and ASPM (abnormal spindle‐like microcephaly‐associated), which are thought to regulate brain size, have been under strong selective pressure since humans left Africa (Evans et al, 2005). However, the team, led by Bruce Lahn, do not claim that these genes are associated with cognitive functions, and others have suggested that they might have undergone selection to cope with the decreasing amounts of good daylight as humans migrated northwards through Europe, Asia and possibly North America. “There is now nice evidence of selection over recent time for genes that promote large brains at high latitudes, such as Bruce Lahn’s work,” Robin Dunbar agreed. “But this is almost certainly due to the need for a larger visual area at high latitudes [where light levels are lower], not for greater intelligence, although this is as yet unpublished data.”
However, human brains have actually decreased by about 10% in volume during the past 30,000 years; the rapid evolution of new cognitive functions—language in particular—might therefore have resulted from structural rather than volume changes.
One explanation for this reverse trend in human brain size is that brains come with metabolic costs attached—the brain consumes about 20% of the basal calories used by our bodies each day—and human evolution might have reached a point where increased metabolic demand outweighed the benefits of greater brain volume. Instead, selective pressures might have begun to favour genes that conferred greater processing efficiency and improved coordination between functional units.
“We should be more concerned with what is likely a distinctively human quality—wisdom—the skill in how to use our intelligence in a way that promotes a common good, over the long term as well as the short term, through the infusion of positive ethical values.”
average brain volume of 1274 cm3 for men, and 1131 cm3 for women
Neanderthals: 1,500–1,800 cm3