Two legs better than four
29 Mar 2012 by Evoluted New Media
Early ancestors began to walk on two instead of four limbs in order to carry as much food as possible and monopolise resources say Cambridge researchers.
By studying modern-day chimpanzees as they competed for food resources, researchers from the University of Cambridge now understand why our hominin ancestors became bipedal.
Their study – published in Current Biology – suggests chimpanzees began moving on two limbs in situations where they need to monopolise resources in short supply. Standing on two legs meant they could carry much more in one go because it freed up their hands.
The team think our early ancestors lived in shifting environmental conditions where some resources were hard to come by, and over time, intense bursts of bipedal activity led to anatomical changes that became the subject of natural selection.
“Bipedality as the key human adaptation may be an evolutionary product of this strategy persisting over time, said Professor William McGrew from the Department of Archaeology and Anthropology. “Ultimately it set our ancestors on a separate evolutionary path.”
Researchers remain divided over exactly when our ancestors became bipedal as there is a lack of evidence in the fossil record. However, it is widely believe they became bipedal because of climactic changes which reduced forested areas and forced them to move longer distances across open terrain more often.
The researchers believe that the need to transport resources with maximum efficiency prompted our ancestors to walk on two limbs. To test this, they monitored the behaviour of chimpanzees to determine when and why they resorted to bipedal movement.
Chimpanzees reaching for different combinations of two nuts showed that the more prized the nut, the more the chimpanzees attempted to move in one go. In such high competition settings, the frequency of cases where chimpanzees started moving on two legs increased by a factor of four.
A second survey showed bipedal movement arose in situations where chimpanzees needed to compete for rare and unpredictable resources.
The researchers conclude that when unpredictable resources – which the chimpanzees regard as valuable – are scarce and access to them is on a first come first served basis, they are more likely to switch to bipedal movement as they can carry more resources at once.
