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发帖数: 29846 | 1 Charles Q. Choi, LiveScience ContributorDate: 26 July 2011 Time: 07:01 PM ET
Brains are larger in those who live farther from the equator — in order to
help them see better, researchers now suspect.
Scientists have long known that brain volume increases with latitude — that
is, the closer one gets to the poles.
"That might be mistaken for implying that intelligence increases with
latitude," said researcher Robin Dunbar, an evolutionary anthropologist at
the University of Oxford. "Our data suggests that this isn't so." [10 Things
You Didn't Know About the Brain]
The investigators noted that the amount of light that reaches Earth's
surface decreases the higher one goes up in latitude. They reasoned that in
order to compensate, both eyeballs and the brain regions linked with vision
might increase in size. Nocturnal primates do have larger eyes than ones
active during the daytime, presumably in order to help them see better in
the dark, and the same holds true for birds that sing earlier in the dawn,
when light is sparse.
Dunbar and his Oxford colleague Eiluned Pearce measured the size of eye
sockets and brains in 55 people from 12 different areas of varying latitude
across the globe, from Scandinavia to Kenya to Australia. They determined
that eyeball size increased with latitude just as brain size did, findings
that are detailed online July 27 in the journal Biology Letters.
The biggest brains belonged to populations who lived in Scandinavia, while
the smallest brains were those of Micronesians, the researchers found.
Under daylight conditions considered typical for each latitude, people from
higher latitudes were found to have the same level of visual keenness as
those from lower latitudes, the researchers noted. However, at dawn or dusk,
when light levels are lower, people from higher latitudes might have
markedly sharper eyesight, though this idea hasn't been tested, the
researchers said.
"In relatively recent evolutionary time, humans have adapted to the low
light levels of high latitudes by adjusting how much light enters the visual
system," Dunbar noted.
The researchers are now looking at a larger sample of brains and eyes and
measuring their dimensions more accurately with modern imaging techniques. |
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