data from:

http://www.as.ua.edu/ant/bindon/ant475/evolution/human.htm

Walking Efficiency - Bipedalism

Why would our ancestors have invested in this awkward way of getting around on the ground?

Human bipedal running is both slower and less energetically efficient than is chimpanzee knuckle-walking or quadrupedalism.

But at a normal walking pace, for instance the way Australopithecus might have gotten from one food patch to another, human bipedal walking is more energetically efficient than is chimpanzee knuckle-walking

Bipedalism would confer an adaptive advantage especially in times of low food availability and sparse distribution of food resources. Bipedal hominids would expend less energy to move from patch to patch of food, and would get there faster on average than knuckle-walking early pongids.
 

Energetic Efficiency

Walking speed Species

Energy cost 
ml 02/kg/hr

Energy cost relative to quadruped

2.9 km/hr Chimp

0.522

149%

Human

0.193

86%

4.5 km/hr Chimp

0.426

148%

Human

0.170

94%

2.9 km/hr is normal knuckle-walking speed of chimps, 4.5 km/hr is normal bipedal walking speed of humans (after Rodman and McHenry 1980)
In a changing environment such as that found at the close of the Miocene, food resources became more sparsely distributed and there was less certainty about the location of food resources as forests shrank and expanded.
The ability to move from one forest/woodland patch to another efficiently would have been adaptive.

Bipedal hominids would have been well suited to do this.

Early Australopithecines appeared to have picked up bipedalism while they retained climbing abilities.
 

                           Copyright © 1998 Nature's Holism by Laurence Evans,  All Rights Reserved.

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