There are many distinct hypotheses as to how and why bipedalism evolved in human

Question

There are many distinct hypotheses as to how and why bipedalism evolved in humans. All evidence points to bipedalism evolving before the expansion in human brain size. The different hypotheses are not necessarily mutually exclusive and a number of selective forces may have acted together to lead to human bipedalism.

1)Postural Feeding Hypothesis

2)Provisioning Model

3)Thermoregulatory Model (heat based)

4)Carrying Models

5)Wading Hypothesis

6)Turn-Over Pulse Hypothesis

7)Other Behavioural Models (There are a variety of ideas which promote a specific change in behaviour as the key driver for the evolution of hominid bipedalism. For example, Wescott (1967) and later Jablonski & Chaplin (1993) suggest that bipedal threat displays could have been the transitional behaviour which led to some groups of apes beginning to adopt bipedal postures more often. Others (e.g. Dart 1925) have offered the idea that the need for more vigilance against predators could have provided the initial motivation. Dawkins (e.g. 2004) has argued that it could have begun as a kind of fashion that just caught on and then escalated through sexual selection. And it has even been suggested (e.g. Tanner 1981:165) that male phallic display could have been the initial incentive.)

Pick one of these "theories" (or another that you find) then write a 1-2 paragraph summary of the theory. Then discuss your opinion of the theory - do you find it plausible? Do you think it is possible as the only reason why bipedalism evolved or must it be in conjunction with another selective pressure?  Make sure that you cite your sources correctly.

Explanation / Answer

Bipedalism (walking upright on foot) in the Homo sapiens distinguish them from their other Pan (apes) relatives. There are a number of suggestive hypotheses regarding the emergence of bipedalism in Homo sapiens. One of this hypothesis is Postural feeding hypothesis. The hypothesis suggests that the earliest hominins started bipedalism to carry a large amount of food over large distances. This theory also indicates that the bipedalism helped them to balance while performing various tasks (collecting food, carrying materials). The provisioning theory supports the idea of postural feeding hypothesis by suggesting bipedalism in humans is because of the need for upright posture for food provisioning and monogamy (Ko, 2015). It is also suggested that the monogamy and bipedalism were related. The male’s job was mainly to collect food and resources for the females who were raising children. Therefore, in order to successfully provide the food, the males started walking upright on two legs as it helped them in finding the much larger amount of food in lesser time. Bipedalism helped both the males and females in food collection and simultaneously raising young ones (Wayman, 2012).

Further bipedalism was also important to save the amount of energy being required to carry out the task of food provisioning. Chimpanzees often use bipedalism while collecting food from trees while balancing themselves on two legs (Hunt, 1996). It ensured carrying energy-rich food in large quantities (like fruits and nuts, meat etc.) without wasting much energy in walking (Richmond et al., 2001). The fact that bipedalism saves a larger amount of energy is evident from a 2017 research on chimpanzees where they used 75% additional energy compared to humans on treadmills (Wayman, 2012).

In my opinion, the postural feeding hypothesis does explain the evolution of bipedalism in Homo sapiens with a lot of reasoning. However, there are a number of other theories that also effectively suggest various causal factors behind bipedalism. Though reasonable, the postural feeding hypothesis cannot be said as the sole explanation for the evolution of bipedalism in Homo sapiens. Also, there cannot be a specified time period suggesting the gradual use of bipedal solely for food provisioning. Evolution is rather a very complex phenomenon resulting from a number of reasons and causations suggesting even a slight change in behaviour to some factors. Multiple forces have pushed the biological evolution of a trait in multiple directions. Therefore, it’s rather difficult to explain the evolution of a trait (bipedalism, in this case) by a simple theory or any particular answer.

References:

Hunt, K. D. (1996). The postural feeding hypothesis: an ecological model for evolution for bipedalism. South African Journal of Science. 92(2). 77-90

Ko, K.H. (2015). Origin of bipedalism. Brazilian Archives of Biology and Technology. 58(6). 929-934

Richmond B. G., Begun, and Strait. (2001). Origin of Human Bipedalism: the knuckle-walking hypothesis revisited. American Journal of physical anthropology. 116(S33). 70-105

Wayman, E. (2012). Becoming Human: the evolution of walking upright. Smithsonian. Dt. Aug 06. Retrieved on 09-07-2018.

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