http://www.nature.com/news/2004/041115/full/041115-9.html
Distance running 'shaped human evolution'
Michael Hopkin
Our African ancestors may have been talented endurance athletes
Long-distance running was crucial in creating our current upright body
form, according to a new theory. Researchers have suggested that our
early ancestors were good endurance runners, and that their habit has
left its evolutionary mark on our bodies, from our leg joints right up
to our heads.
Early humans may have taken up running around 2 million years ago,
after our ancestors began standing upright on the African savannah,
suggest Dennis Bramble of the University of Utah, Salt Lake City, and
Daniel Lieberman of Harvard University in Cambridge, Massachusetts. As
a result, evolution would have favoured certain body characteristics,
such as wide, sturdy knee-joints.
The theory may explain why, thousands of years later, so many people
are able to cover the full 42 kilometres of a marathon, the
researchers add. And it may provide an answer to the question of why
other primates do not share this ability.
" Everyone says humans are bad runners. There's no question we're
appalling sprinters, but we're quite good at endurance running. "
Daniel Lieberman
Harvard University
Our poor sprinting prowess has given rise to the idea that our bodies
are adapted for walking, not running, says Lieberman. Even the fastest
sprinters reach speeds of only about 10 metres per second, compared
with the 30 metres per second of a cheetah. But over longer distances
our performance is much more respectable: horses galloping long
distances average about 6 metres per second, which is slower than a
top-class human runner.
"Everyone says humans are bad runners, because when you think of
running you tend to think of sprinting," he adds. "There's no question
we're appalling sprinters, but we're quite good at endurance running."
Race training
How did we get so good at running? Scavenging is the best answer,
Lieberman suggests. Our savannah ancestors would have been in
competition with hyenas, who are also good long-distance runners, to
get to the site of a big kill and pick over the remains. "You could
see a flock of vultures on the horizon and just take off towards
them," he says. Or perhaps early humans used their endurance simply to
chase prey to exhaustion.
The theory makes sense of a raft of human characteristics, Bramble and
Lieberman write in this week's Nature1. Not only do we have springy
Achilles tendons and stout leg-joints, our hairlessness and tendency
to sweat make us very good at dissipating heat.
Running may even have improved our balance, says Fred Spoor, who
studies human evolution at University College London. "Running
requires a lot of delicate coordination: your legs are off the ground
and you need to coordinate your eyes to see where your foot will
land," he says.
Many animals keep their balance with the aid of semicircular canals in
the inner ear, which are filled with fluid that acts as an
acceleration detector. These structures are unusually large in both
modern humans and our evolutionary cousin [censored] erectus and this shows,
says Spoor, that they might have helped primitive runners stay on
their feet.
In fact, running seems to be the only reason that we have prominent
buttocks, says Lieberman. He has measured the activity of the gluteus
maximus muscle in volunteers during a walk and a jog. "When they walk
their glutes barely fire up," he says. "But when they run it goes like
billy-o."
It remains to be seen how the theory will be received, says Spoor. If
correct, it means that the genus [censored] is unique among primates in its
running ability. But some experts maintain that there is nothing
special about human locomotion, and what separates us from other apes
is simply our outsized brains.