Causes of Bipedalism: Postural Feeding

Outline

A theory that has been revitalised since the discovery of Lucy suggested that bipedalism did not occur on the savannah. If Australopithecus afarensis lived in a wooded environment it is logical to expect an explanation for bipedalism that relies on bushes and woodland. The strength of the theory is that postural feeding is the most commonly observed form of facultative bipedalism in chimpanzees. The main weakness is that it does not explain why all chimpanzees did not become bipedal.

Authors

Attributed to de Brull (1962) but championed more recently by Hunt (1994). Many other similar theories have been proposed based on postural feeding e.g. grass seed feeding. (Jolly 1970)  

Location

Woodland.

Selection Pressure

The individual selection pressure for an individual that is better able to feed whilst standing on its hind legs 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. One certainly would expect the posture to be totally upright if their bipedalism was for this purpose.

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

A popular theory. Listed in 5 out of 8 of my sample textbooks.

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