Theory blends 'Deep Impact' with Darwin
 
Did cosmic catastrophes play a part in evolution of modern humans?

http://www.msnbc.com/news/563983.asp
By Robert Roy Britt
SPACE.COM
 
 April 24 -  In the 5 million years or so that it took for apes to become
human, many humanlike branches of the evolutionary tree were lopped
off. Scientists have long wondered why these other hominid species,
estimated to number a dozen or more, didn't make it. Were those who
came to travel to the moon and ponder their very origin the logical and
inevitable victors in the most important of all Darwinian struggles? Or
did we just get lucky?

A NEWLY PRESENTED mathematical argument suggests that the birth of
Homo sapiens was guided by catastrophic asteroid or comet impacts,
which created climate conditions that competing species, frankly, couldn't
handle.

       It also holds that our human ancestors avoided early elimination by
the statistical skin of their rotting teeth.

       "The reason that Homo sapiens have survived in spite of these
global disasters has little to do with the traditional explanations given by neo-
Darwinists," said Benny Peiser, a social anthropologist at Liverpool John
Moores University. "It is sobering to realize that we are alive due to
cosmic luck rather than our genetic makeup."

       Peiser bases his argument on the fact that populations of hominids
and early modern humans were extremely small. "Had any of these impacts
occurred in the proximity of these population groups, we might also have
gone the way of the dodo," he said.

       The study's assumptions and calculations have met with strong
caution and even sharp criticism among scientists who specialize in evolution, as
well as asteroid experts.

ADAPTIVE ADVANTAGE
         David Balding, a professor of applied statistics at University of
Reading in Britain, said the idea that human survival is due to "cosmic luck" does
not compute:

       "Perhaps we were lucky in avoiding a massive impact, but perhaps it
was our adaptive advantage that helped us survive modest regional impacts whereas
our hominid cousins did not," said Balding, whose own research focuses on
human evolution.

       But some called the new scenario plausible. It has not been
published in a peer-reviewed journal, but it is based on impact estimates that are generally
accepted by the asteroid research community, though there are disagreements over the
precise number of times a large asteroid or comet has struck our planet.

       Peiser laid the idea out earlier this month at a conference,
"Celebrating Britain's Achievements in Space." He worked with Michael Paine, a volunteer for the
Planetary Society in Australia who ran impact scenarios through a computer program.
(Paine has written freelance stories for Space.com in the past.)

       The researchers concluded that there would have been 20 "globally
devastating"  impacts during the past 5 million years, with effects strong enough to
have had "a catastrophic and detrimental effect" on human evolution. Five million
years ago is roughly the time when hominids diverged from other apes, though some
recent controversial evidence puts the split as far back as 6 million years ago.

Did space rocks set the human stage?
       No one argues that asteroids can be devastating when they tangle
with Earth. An impact 65 million years ago is widely believed to have spurred the
demise of the dinosaurs and many other animals and plants.
 
[balance at http://www.msnbc.com/news/563983.asp]

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