University Assignment: Thermoregulatory Model of Bipedalism Analysis

This assignment is an essay that analyzes the thermoregulatory model of bipedalism, a theory proposed by Peter Wheeler in 1984, which suggests that bipedalism evolved to increase body surface area for heat dissipation and reduce heat gain. The essay discusses the model's strengths, such as the reduction of body hair and the sweat cooling mechanism, and its weaknesses, including the questionable assumption of early hominids being directly exposed to the sun in open savannahs and the lack of applicability to wooded habitats. The essay explores how bipedalism aided in hominin survival by preventing direct sunlight exposure and enabling efficient use of limbs for survival and food availability. The essay references key literature and concludes that bipedalism was a beneficial adaptation for hominins.

Running Head: TWO LEGS ARE BETTER THAN FOUR
Assignment 3: Two legs are better than four
Name of student:
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Author Note:

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Assignment 3: Two legs are better than four
Introduction
Bipedalism is a mode of terrestrial locomotion were the animal uses the rear limbs for
locomotion (Ko, 2015) Walking, running and hopping can be considered as different types of
bipedal movement. The majority of the vertebrates are quadrupeds and only a countable
number fall in the biped category. The possible reasons of evolution of human to bipedalism
includes freeing of the arms allowing the hominids to make and use tools successfully, they
could use their hands for communication and gathering food (Trevathan, 2017). There are
twelve distinct models in support of bipedalism and human adaptation of bipedalism. In this
article, thermoregulatory model of bipedalism is discussed.
Discussion:
Thermoregulatory Model
Thermoregulatory model of bipedalism was proposed by an evolutionary biology
professor, Peter Wheeler in the year 1984. According to the theory, bipedalism increase the
surface area of the body hence resulting in heat dissipation and reducing heat gain (McKee,
Poirier & McGraw, 2015). Wheeler explained with observation that when hominids are taller
than or equal to 1.25m the have an advantage of convective cooling over individual shorter
than 1.25cm. When the hominids are at an elevated position in comparison to the ground they
can avoid direct exposure to the sun and experiences higher wind speed that promotes the
heat dissipation, hence this made organisms feel more comfortable. Sweating is a distinctive
feature in human physiology as well as human anatomy that enhances the capacity of the
body to cool itself. The process of sweating ensures heat loss by evaporation. It requires
approximately 580 calories to transform 1gram of water to vapour at 35⁰C.this phase
transition helps in transforming and dissipating the considerable amount of energy in the
form of heat to the atmosphere from the organism. Hence, this results in cooling the body

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Assignment 3: Two legs are better than four
surface where the transition had occurred. Wheeler explained this by using two putative
hominid ancestors. One of the ancestors were positioned in quadrupedal posture while the
other one was positioned in bipedal posture. The observations were considered by taking
pictures of the two postures from different angles with respect to the position of the sun. It
was inferred from the study that bipedal posture reduced the body surface area exposed to the
sun rays. The mammals inhabiting the savannah have a specialised set of adaptation called
‘carotid rete’ that protects their brain from overheating.
Strength and Weakness of the Model
The key strengths of this model includes reduction of hair in the body and sweat cooling
mechanism adoption in support with bipedalism caused the evolutionary changes in human
making them distinct from their ancestors. These are the major promising advantages of the
thermoregulatory model on bipeds over quadrupeds in an equatorial habitat (David-Barrett &
Dunbar, 2016).
There are various weaknesses of this thermoregulatory theory. The first being that
positioning early hominids under the direct sun rays in open savannah is not a reasonable
explanation to add in to survival (Hanna & Tait, 2015). There is no analogues in extinct
mammals even if the primates are not considered. His study dealt with the paleoecology of
early savannah based hominids. This model majorly deals with hominids of savannah habitat
but there is no explanation on the impact of bipedalism on hominids of wooded habitat.
Conclusion
It can be concluded from the above article that bipedalism was a beneficial adaptation for
the hominins as it aided in survival of the individual as well as its offspring. It is evident that
it prevents the hominins from direct exposure to sunlight and ensures efficient use of the

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Assignment 3: Two legs are better than four
limbs to survive from predation, for food availability. Hence, proving that two legs are better
than one.

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Assignment 3: Two legs are better than four
References
Dávid-Barrett, T., & Dunbar, R. I. (2016). Bipedality and hair loss in human evolution
revisited: The impact of altitude and activity scheduling. Journal of human
evolution, 94, 72-82.
Hanna, E., & Tait, P. (2015). Limitations to thermoregulation and acclimatization challenge
human adaptation to global warming. International journal of environmental research
and public health, 12(7), 8034-8074.
Ko, K. H. (2015). Origins of bipedalism. Brazilian archives of biology and technology, 58(6),
929-934.
McKee, J. K., Poirier, F. E., & Mcgraw, W. S. (2015). Understanding human evolution.
Routledge.
Trevathan, W. R. (2017). Human birth: An evolutionary perspective. Routledge.