[ExI] Gene shifts
hkhenson at rogers.com
Sun Sep 21 02:57:16 UTC 2008
The below article is indirect support for Gregory Clark's
concepts. He makes that case that genetic selection for traits he
deems "capitalist" during the 20 plus generations proceeding the
industrial revolution. That he thinks set the stage for the
You would expect a different set of trait to be advantageous to
reproduction in different kinds of societies. "Impulsivity and a
short attention span" seems to be one of them that was selected
against in the history of western Europe. When you think about it,
that's about what you would expect. :-)
Did hyperactivity evolve as a survival aid for nomads?
11:39 10 June 2008
NewScientist.com news service
Impulsivity and a short attention span may be the bane of every
parent with a hyperactive toddler, but those same traits seem to help
Kenyan nomads keep weight on.
A gene mutation tied to attention deficit hyperactive disorder (ADHD)
is also associated with increased weight among a chronically
undernourished group of nomads called the Ariaal. Notably, the
mutation offers no such benefit to a cousin population that gave up
the nomadic lifestyle in the 1960s.
The nomads' active and unpredictable life centred on herding might
benefit from spontaneity, says Ben Campbell, an evolutionary
anthropologist at the University of Wisconsin at Milwaukee, US, who
was involved in the new study.
"If you are a nomad then you ought to be little more impulsive than
if you are settled," he says. "You should be a little quicker on the
The Ariaal are an isolated group of nomads who wander around northern
Kenya, herding cows, camel, sheep and goats. Encouraged by Christian
missionaries in the 1960s, some members settled in the same region
and started relying on agriculture for some of their food.
The nomads and the settled groups still interact and intermarry, but
they live drastically different lifestyles. "The nomads are always
doing something. They are always walking to herd their animals,"
Campbell says, while settled Ariaal tend to be sedentary.
A previous study found that nomadic cultures around the world tend to
have the same mutations, which determines the brain's response to a
pleasure-delivering chemical called dopamine and is linked to
impulsivity and ADHD.
Campbell and his colleague Daniel Eisenberg, of Northwestern
University in Evanston, Illinois, US, looked for the mutation in 87
settled and 65 nomadic Ariaal men.
About a fifth of the men from each group had the mutation. However,
their physiques differed. Nomads with the mutation, which is in the
gene called DRD4, tended to have slightly higher body-mass indexes
and more muscles than nomads without the mutation ? though both would
be considered undernourished by Western standards. No such difference
existed in the settled Ariaal.
Why the mutation isn't more common is a mystery, says Eisenberg.
Another study found the impulsive variation in about 60% of native
South Americans, but only 16% of Caucasian Americans. "It might be
that there is a niche for a few people with more impulsive behaviour,
but when there are too many of them those niches are filled," he says.
Also unexplained is how a gene linked to ADHD promotes greater body
weight in nomads, and not village dwellers. Campbell speculates that
a short attention span and penchant for risk taking could benefit
nomads who don't know where the next meal will come from.
However, the mutation could also make food more gratifying, or it
might affect how the body converts calories to kilograms. "We really
don't know," Campbell says.
The mutation "predisposes you to be more active, more demanding, and
not such a pleasant person," says
Henry Harpending, an anthropologist at the University of Utah in Salt
Lake City, also in the US. "You probably do better in a context of
aggressive competition." In other words, in lean times, violent men
may feast while passive men starve.
Journal reference: BMC Evolutionary Biology (DOI: 10.1186/1471-2148-8-
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