Your own two feet
Bipedalism – walking on two feet – is one of the defining features of humans
The last common ancestor of chimpanzees and humans probably had a quadrupedal gait, walking on its knuckles as chimpanzees do now.
Walking upright would have had advantages, as it is more energy-efficient and would have permitted foraging farther afield. It has its disadvantages, though, particularly in the strains it imposes on the backbone, which may be why back complaints are now so common.
Bipedalism also calls for good balance and coordination. Some forms of brain damage can lead to difficulties with locomotion (ataxia). This is a symptom of some inherited conditions, although there are also non-inherited causes including alcoholism and tumours. In 2006 the Turkish researcher Uner Tan discovered an extended family that walked on all fours in a ‘bear crawl’.
Controversially, Tan has suggested that people with ‘Uner Tan syndrome’ illustrate a step backwards in evolution towards a more primitive gait. The more accepted view is that family members have difficulty balancing on two legs and tend to stand or use this adapted crawl rather than learning to crawl conventionally when infants. Unlike our presumed ancestor, members of this family do not use their knuckles to walk on.Lead image:
Anthea Sieveking/Wellcome Images CC BY NC ND