http://www.newscientist.com/news/news.jsp?id=ns99992547
Human brain "paid off" by long life
22:00 15 July 02
Robin Orwant
A theory portraying children as start-up companies and middle-aged
adults as their investors has been proposed to explain why humans have
such big brains and long life spans.
Evolutionary biologists have puzzled for decades over why humans live
twice as long as chimpanzees and gorillas and have brains three to
four times larger than their closest living relatives.
"We're thinking of the brain as an investment," says economist Arthur
Robson, at the University of Western Ontario. Robson and
anthropologist Hillard Kaplan, at the University of New Mexico,
believe this investment is so substantial that it requires a longer
human life span to give it the time to pay off.
"The combination of issues that they raise is novel - a useful first
step," says evolutionary biologist Michael Rose, at the University of
California at Irvine. But he warns against putting too much confidence
in a mathematical model: "If you're a good applied mathematician, you
can come up with a model to give you any conclusion you want."
Nonetheless, Rose is intrigued by the explanation of why human
children are so unproductive for so long. "This is the best paper on
the evolution of teenagers I've ever read," he says.
Enormous debt
The inspiration for Robson and Kaplan's theory came from the
observation that children in modern day hunter-gatherer societies
consume more calories than they produce, accumulating an enormous debt
that peaks at age 20.
As active young adults, they produce more than they consume, but it
takes decades to pay off their childhood debt. Only at age 50 do they
start moving out of the red and into the black. They then begin to
make a net contribution of resources to their society, offsetting the
debt of the children in the next generation.
The researchers noticed the parallels between the energy flows in
these societies and cash flows in start-up companies, and applied an
economic model to human evolution. They treated physical and mental
capacities as "embodied capital", with the brain representing a
special form of capital that increases in value over time.
Predator protection
According to the model, the brain requires such an enormous investment
of energy during childhood that human ancestors must have evolved long
life spans to make that initial investment worthwhile.
Robson and Kaplan believe these early humans must have lived in an
environment where food gathering was complicated, favouring the
development of big brains. They also suspect that the environment
reduced the risk of premature death by affording some protection from
predators.
The model therefore assumes that the environment was the key factor
shaping human evolution. But, Rose argues, this leaves out the
sophisticated social interactions that must have also contributed to
development.
Journal reference: Proceedings of the National Academy of Sciences
(DOI: 10.1073/pnas.152502899)
22:00 15 July 02
Ian Goddard : http://users.erols.com/igoddard
"To lengthen thy life, lessen thy meals." Benjamin Franklin
From Fat to Thin: http://users.erols.com/igoddard/me-cr.htm
Caloric Restriction: http://users.erols.com/igoddard/cr.htm
