The ancestors of humans began walking upright
while they were still living in trees, and not out on open land,
according to a theory which was published in 2007.
The traditional view up to this point had been
that bipedalism evolved gradually from the four-legged
'knuckle-walking' displayed by chimpanzees and gorillas today.
The new study was published in the journal Science, disputing
the established idea.
The British authors of the study stated that
upright walking was always a feature of great ape behaviour.
Humans inherited it without ever passing through a knuckle-walking
phase. They believed that knuckle-walking evolved only recently
as a way of getting around on the forest floor.
Susannah Thorpe, Robin Crompton, and Roger Holder
came to their conclusions after analysing the movement of wild
orangutans, which spend most of their lives in trees. They found
that orangutans used upright locomotion to fetch food from the
small branches of trees and to cross directly from one tree to
Both access to fruits and crossing gaps in the
trees would require an ability to navigate very thin, terminal
tree branches which are liable to bend under body mass. The logical
conclusion from the environmental, fossil, and experimental evidence
is that upright, straight-legged walking originally evolved as an
adaptation to tree-dwelling.
They suggested the shift made by our ancestors
to a terrestrial lifestyle came about as climate change thinned
out their forest habitat.
In response, these ancient hominids may have
abandoned the high canopy for the forest floor. Here, they
remained bipedal and began eating food from the ground or from
smaller trees. The act by orangutans of walking upright on
springy branches is much like athletes running on springy tracks -
they use extended postures of knee and hip to give them straighter