The ancestors of humans began walking upright while they were
still living in trees - not out on open land, according to a new
The traditional view is that bipedalism evolved gradually from
the four-legged "knuckle-walking" displayed by chimpanzees and
Now, a study published in the journal Science disputes this
The British authors of the study say that upright walking was
always a feature of great ape behaviour.
Humans inherited it without ever passing through a
They believe that knuckle-walking evolved only recently as a way
of getting around 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
"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," said Professor Robin
Crompton, from the University of Liverpool.
"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 suggest the shift made by our ancestors to a terrestrial
lifestyle came about as climate change thinned out their forest
In response, these ancient ape-like creatures, or hominids, may
have abandoned the high canopy for the forest floor. Here, they
remained bipedal and began eating food from the ground or from
Professor Crompton explained that orangutans walking upright on
springy branches act much like athletes running on springy tracks -
they use extended postures of knee and hip to give them straighter