Sexual Preferential Theory * Original name: Carrying Hypothesis * Theory by: Owen Lovejoy

* “The behavioral model, as presented by Lovejoy, focuses on social behavioral mechanisms that influence survivorship and birthrate. Human sexual behavior and anatomy are hypothesized as implying a monogamous mating structure, a social form seen as prerequisite to male provisioning. Provisioning behavior with the upper limbs used to transport food to a mate and offspring is seen as a strong selection factor for bipedality by directly improving offspring survivorship and increasing reproductive rate.”

* This hypothesis based on sexual preference, generally. Due to the drought that happened 5 million years ago in the East of Africa, hominids had to look for new sources of food. As the male would be away for a long duration due to his search for food, monogamy was passed in order to keep his woman not to be involved with other men. His responsibility would mean, he would have to provide for his woman and carry the food. The man was able to carry it because his hands were free and walking bipedally instead of walking quadrupedally.

On the Lookout Theory * Original Name: Vigilance Hypothesis * Theory by: Raymond Dart

* “Raymond Dart's vigilance hypothesis described a situation where early hominids who stood upright would have the benefit of seeing over tall savanna grass (Dart 1926). This would allow them to see predators from a distance. Additionally, their other sense organs would be elevated with bipedalism.”

* This hypothesis/theory states that early hominids stood upright in order to have a better view of what’s over the tall savanna grass and would allow them to see possible predators coming from a distance. As one stands upright over the grass, the upper body will be elevated and only 2 limbs will support you from the ground.

Aquatic Phase Theory * Original Name: Aquatic Ape Hypothesis * Theory by: Alastair Hardy & Elaine Morgan

* “The AAH suggests that many of the features that distinguish humans from their nearest evolutionary relatives can be explained through a period of aquatic adaptation in which protohumans spent time wading, swimming and feeding on the shores of fresh, saline or brackish waters (though there has been disagreement and modification of the theory regarding the salinity of the purported watery environment)and suggests comparisons with other aquatic or semiaquatic species with similar characteristics.

* Hardy and Morgan argue that our ancestor, specifically those located near the seacoast, underwent an aquatic phase. Evidences prove that with human fat aided buoyancy and allowed them to wade through the shallow waters, controlled breathing as they go deeper, relative hairlessness and hands perfect for gripping, handling and eating shellfishes.

Body Temperature Theory * Original Name: Heat Hypothesis * Theory by: Peter Wheeler

* “Peter Wheeler suggested that bipedalism evolved to avoid overheating. He noted that a bipedal hominin exposes only 7% of its surface to sunlight, whereas quadrupeds expose 20% of their surface to the sun. Wind speed is greater and temperatures lower only a meter above the level baboons are forced to walk in, he found, and bipeds lift their torsos into this cool zone.”

* Since most hominids reside in the grasslands of the African savanna, they experience really hot weather. By standing up, they will be exposed to cooler air since air moves and circulates faster on higher altitudes than it is from the ground and solar radiation on the body will be lessened. He also insinuated that by becoming bipedal through this means, sweat also evolved.

Energy Conservation Theory * Original Name: Energetic Efficiency Hypothesis * Theory by: Rodman, McHenry, Steudel, Leonard and Robertson

* “The increased efficiency of transportation has been noted as a possible cause of the shift to bipedalism (Rodman and McHenry 1980). These authors concluded that human bipedal walking is at least as efficient as quadrupedal locomotion in general, and more efficient than chimpanzee quadrupedality specifically. A major problem with the energetic efficiency model of bipedalism is that early hominids did not have the morphological adaptations necessary for efficient bipedalism (Steudel 1996). It would be counterintuitive to assume that they would evolve an awkward new form of locomotion.”

* These authors inferred that human bipedal walking is as efficient as quadrupedal locomotion but a lot more efficient than chimpanzee quadrupedality.

BIBLIOGRAPHY:

Friedman '06, Michael J., "The Evolution of Hominid Bipedalism" (2006). Honors Projects. Paper 16. http://digitalcommons.iwu.edu/socanth_honproj/16 Jacobs, J.Q. (1990). The origin of bipedalism. Retrieved from http://www.jqjacobs.net/anthro/paleo/bipedalism.html

Hunt, K.D. (n.d.). Evolution of bipedalism. Unpublished manuscript, Department of Anthropology, University of Indiana, Indiana, US. Retrieved from http://www.indiana.edu/~semliki/PDFs/BipedalBirx.pdf

Aquatic ape theory. (n.d.). Retrieved from http://en.wikipedia.org/wiki/Aquatic_ape_hypothesis#The_hypothesis