Causes of Bipedalism: Suspensory Feeding

Outline

Another theory revitalised since the discovery of Lucy. Like others it attempts to explain bipedalism in an arboreal environment. Increasingly popular as the savannah has become gradually discredited as the location for the origin of bipedalism. It has the strength that a number of primates have been observed 'running' along branches in trees bipedally and so, as a model that might work in a wooden environment it is attractive. Like postural feeding, it is commonly observed in chimpanzees. Unfortunately, it suffers from the same weakness that it does not explain why all chimpanzees did not become bipedal.

Authors

Attributed to Tuttle (1975.) 

Location

Woodland.

Selection Pressure

As with the postural feeding idea the individual selection pressure for an individual that is better able to feed whilst standing on its hind legs in trees is clear. It is more difficult to argue that moving on two legs would also be selected for, except potentially as a slight time and energy saver.

Intermediate Steps

As existing apes do often get up onto their hind legs to perform a this behaviour it at least has a solid starting point. However it is hard to see how this pressure alone would select traits that would lead to full bipedalism.

Both Sexes?

Both sexes would equally be selected for.

Explains Australopith Anomalies

Australopith morphology is ambiguous as to whether it favoured upright  or 'bent-hip-bent-knee' posture. It is possible that bent-hip bent-knee would be a suitable posture for this arboreal form of bipealism.

Why not Pan? Observed in Pan?

This is where the theory is at its weakest. If this was the only factor contributing to bipedalism why didn't other apes adopt it too?

Links with other Theories

This theory is very compatable with most of the other theories however, because it assumes a woodland, not savannah habitat, it largely contradicts Wheeler's hypothesis.

Popularity

Listed in 2 out of 8 of my sample textbooks.

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