Many consider our first steps our first milestones. It is one of the most important developments for an individual. It was also the beginning of our development as a species. Bipedalism is the ability to walk on two rear limbs or legs. Charles Darwin believed that bipedalism was an evolution by natural selection. (Freidman 2006) However, fossil records do not provide enough information about the origin of bipedalism. There are many other theories on how our ancestors went from being quadrupeds to bipeds. One theory is the postural feeding hypothesis by Kevin D. Hunt in his article “The Postural feeding hypothesis: an ecological model for the evolution of bipedalism”. Owen C. Lovejoy created the provisioning hypothesis which can be found in his article “The Origin of Man”. Gordon W. Hewes has a similar hypothesis to Lovejoy but not completely the same in his article “Food Transport and the Origin of Hominid Bipedalism” Another theory for bipedalism is the thermoregulatory model created by P.E. Wheeler and is discussed in the article “Bipedality and hair loss in human evolution revisited: The impact of altitude and activity scheduling” by Tamas David-Barrett and Robin I.M. Dunbar. While all theories have been criticized, they all show how early hominids had to adapt in order to survive.
Kevin D. Hunts based his postural feeding hypothesis off chimpanzee ecology and Australopithecus morphology. Hunt discusses how chimpanzees are often most bipedal when eating small fruits on open forest trees. Hunt states that chimps get these fruits by either balancing on branches in a semi-hanging arm posture and reaching for them or reaching for the fruit with their arms while their feet are on the ground. (Hunt 1996) The reason for Hunts bringing this up is because chimpanzees are our closest living relatives. Also, Australopithecus had both ape like and human like features. Hunts makes an in-depth comparison of chimpanzee postures to early hominid while gathering food to support his hypothesis of bipedalism. Hunts states that postures such as hanging of the arms and vertically climbing on trees are what created the adaption of bipedalism. (Hunts 1996) While early hominids gathered fruit, they developed the torso structure and their changes to arm hanging also increased and developed. (Hunts 1996) Hunts goes on to say that early hominids developed arboreal bipedal from fruit gathering which evolved over time into what we know as bipedalism today.
In the article “The Origin of Man” by Owen C Lovejoy, Lovejoy suggests the provisioning hypothesis which states that in many species including early hominids a sexual division of labor occurs between provisioning and parenting because offspring are normally immature at birth and immobile. (Lovejoy 1981) Lovejoy focused heavily on social behaviors that influenced survival and birth. (Lovejoy 1981)He theorized that our early ancestor’s had a monogamous structure of mating and walking upright was viewed as a strong selection factor because it meant the male could carry food to his mate and offspring. (Lovejoy 1981) Lovejoy states “Oral carrying would have been inadequate for early hominids, however, and a strong selection for bipedality, which would allow provisions to be carried “by hand,” would thus accompany provisioning behavior” (Lovejoy 1981) The benefit of the male being able to carry more food is that it increased the survival rate for the offspring. Therefore, males tried to walk upright to get a mate. While it is true that reproduction is a driving force in most primates today, there is no proof that early hominids were monogamous; also it does not explain why females are also bipedal if the males were providing them with food. In actuality, It seems unlikely that Lovejoy’s theory can be concretely proven.
While Lovejoy seemed to be on the right track with bipedalism relating to gathering food, it would seem unlikely it was simply to impress females. Food is an essential part of survival for any living thing. Today, we use our hands to grab our food and drinks but imagine not having the ability to stand upright and be able to efficiently grab something to eat. This is an argument brought upon by many when discussing bipedalism and Gordon W. Hewes discusses this theory in his article “Food Transport and the Origin of Hominid Bipedalism”. Hewes states “I believe that the only activity likely to have had the capacity to trans form a mainly quadrupedal ground-dwelling Primate into an habitual biped would have been food transport from the places where food was obtained to a home base where it was consumed. Such carrying could only be accomplished efficiently by an animal with arms and hands for grasping and holding.”(Hewes 1961) Our ancestors had to be scavengers back then and carrying large carcasses or large limbs would have definitely been difficult for a quadruped. Also, being a scavenger means sometimes having to steal food from others so holding food with your hands while using your legs to run would make it easier to get away with the food. (Hewes 1961) However, Hewes did not believe that bipedalism came overnight, he proposes that “It is likely that spurts of running with the load clasped against the chest, as we have seen in macaques, came before the development of an even-paced stride with a well-balanced load. Running rather than walking, for an animal not yet anatomically well adapted to upright locomotion, would be easier on account of the arrangement and function of the leg muscles (Hexton 1947).” (Hewes 1961) Being bipedal allowed our ancestors to be more efficient.
Thermoregulatory model by P.E. Wheeler argues that bipedal locomotion is an adaptation to reduce heat load when roaming in more open habitats. In the article “Bipedality and hair loss in human evolution revisited: The impact of altitude and activity scheduling” Barrett and Dunbar explain “Unlike their great ape sister species that remained within the tropical forests, early hominids began to make increasing use of forest edge and more open woodland (but probably not open savannah) habitats where exposure to the direct rays of the sun was considerably greater, especially during the hottest times of the day when the sun is overhead.” (Barrett et al. 2016) Thermoregulatory model suggests that early hominids tried to reduce the effects of heat as temperatures increased by walking upright. Bipedalism increased the amount of body surface area, which helped reduce heat intake. (Barrett et al. 2016) Wheeler also believed that while walking upright hominids gained access to cooler wind speeds and temperature by being higher above ground. (Barrett et al. 2016) So hominids would feel more comfortable with higher wind flows and heat reduction. This theory has also been used to explain hair loss on the body. (Barrett et al. 2016) Hominids were also able to retain more body water while being bipedal because of the reduction of high temperatures. (Barrett et al. 2016) Bipedalism seemed to be a favorable trait which allowed many benefits.
In conclusion, there are many theories on the evolution of bipedalism. Whether bipedalism evolved from the postural feeding hypothesis, provisioning hypothesis, the thermoregulatory model, or all three; it is clear that early hominids were facing a lot of environmental pressure to adapt. All of these theories have been largely scrutinized and the truth is, we are not a hundred percent sure how we became bipedal but it seems with walking upright came many other advancements. With bipedalism came larger brains and the ability for higher intelligence which made us who we are today. If bipedalism would have never happened, perhaps we would still be in the trees of the rainforest or even extinct given all the climate change. Our first steps were and still remain our most important milestone.