What are 2 propsed causes of bipedalism?

Question

What are 2 propsed causes of bipedalism?

Answer 1

The "Reaching up" theory, in that we had to gather food from a standing position, and then carry it home. Also, they believe that living in the grasslands, it was beneficial to stand up because it is more efficient, and you can also see further. Bipedalism is also a more efficient way of dealing with heat, since you get more wind and less sunlight on your back than you would if you were on hands and feet.

Answer 2

Creation.

Some creatures are designed to walk on 2 feet, some on four.

There is nothing to suggest that one changes to the other (except evolutionary wishful thinking)

Answer 3

1. Humans were designed to walk on two legs.

2. Other primates were designed otherwise.

"Reaching Up" theory? That one goes against science. If I lose my arm, my children will still be born with two. If I become a body-builder, my kids will still be born weak. My actions in life will not effect a change in my DNA.

The walking ape in the Israeli zoo is sick. That is why she walks upright. If she lived in the wild, she would not survive. She is a bad argument for evolution, and a good argument for intelligent design.

Answer 4

One is that it was to see further, over the high grasses of the African savannah. The most likely, however, is provisioning theory; to enable the males to supply the females with  meat, from their hunts, or even larger quantities of fruit, which those females encumbered with small offspring would have difficulty accessing, and thereby gaining more opportunties to mate. ~~~~~ About Alopecia Areata (male pattern baldness) :

Alopecia areata is a particular disease affecting hair growth in the scalp and elsewhere. The loss is the cause of great concern to those affected, ...

home.vicnet.net.au/~aasa/About%20Alope... - 13k - Cached - Similar pages - Note this:

My intention here is to refute the above assertion, that Alopecia Areata is a disease (it is not more a disease than the relative hairlessness of Homo Sapiens Sapiens is, compared with, say Pan Troglodytes [the chimpanzee] ). Instead, it should be regarded as an evolutionary adaption.

ALOPECIA AREATA (MALE PATTERN BALDNESS):                                                                                                                                                                                                          Has a great deal to do with the fact that human beings (Homo Sapiens Sapiens) are a relatively hairless, and physically weak, (chimpanzees are several times stronger, yet smaller) and need a lot of high nutrient foods to maintain their large brains.                                                                             Those brains can take up to 40% of the blood pumped by the heart*. We are somewhat like sponges, perspiring a great deal, when compared with other primates.                                                                                                                                                                                                                                We evolved in tropical, and sub tropical East Africa, in the enormous rift valley, with its many and variable environments, from a group of hominins (on the evolutionary path leading to Homo Sapiens Sapiens).    

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We have only adopted regular bathing very recently. For millions of years, our ancestors never bathed. During sexual intercourse, the areas covered by the pubic hair on the male and female come into repeated contact. If it wasn't for the retention of that pubic hair, the stickiness involved in the partial drying of sexual fluids would have caused skin to be peeled off, exposing the area to infection (flies, as vectors of disease/parasites).                                                                                                                                                                                                                                                                                  No doubt, this is what happened to some groups, which were devoid of pubic hair, to the same extent that we are relatively hairless in other parts of our body. They were selected against, in the evolutionary pool, just like those which were uniformly hirsute, and unable to forage, scavenge, and hunt in the heat of tropical/subtropical Africa, in the middle of the day, because, for them, as with the big cats, it was too hot to do anything but lie down in the shade. As a result, those with less body hair had little competition, and were able to provision the females in their tribe better, receiving more sexual favours as a result of "bringing home the bacon", thereby producing more offspring, bearing similar characteristics. Our ancestors got the best of both traits, perpetuating them to this day.                                                                                                                                                                                                                                                                                                        In my view, male pattern baldness is an evolutionary adaption: an extension of bodily hairlessness (note: it occurs rarely in females, and usually only manifests in males after sexual maturity is attained. It would serve no purpose in females, since they remained in the shade, with their offspring, and may have developed in some groups of males at an early age, but skin cancer takes around 25 years to occur, after initial exposure, so those in which baldness developed early would start to be eliminated, not only by the skin cancer, but by the preference of the females for mating with males displaying no apparent physical defects. In those males in which it developed later, however, by the time skin cancer had developed, their reproductive life would have been over, since they died at a much younger age than we do).                                                                                                                                                                                                                                                      That thinning of the hair on the head, when combined with a male human's high rate of perspiration, and adequate airflow of low humidity air produces a significant increase in the cooling effect to the brain*, which acts to some extent in a manner similar to the radiator of an automobile. This is supported by the fact that males tend to perspire more than females, who, because they were not highly active in the hottest parts of the day, were not selected for that particular                                                      trait.                                                                                                                                                                                                                                                              In the Amazon jungle, the local tribes perspire very little, despite the heat, owing to the fact that the high relative humidity minimises the effectiveness of perspiration as a cooling mechanism. Incidentally, in every documentary I have ever seen of such natives, like the Yanomamu, I have yet to see one with noticeable alopecia. Note too the lack of facial hair, and chest hair on many Polynesian men. It only takes 30 - 40 generations, to bring about significant changes in a population.

Answer 5

I think it was just a quicker way to get up a tree, anyway, there is a news story about an ape in the Israel zoo that started walking upright after a long stomach illness that almost killed it.

Answer 6

Geophysical upwelling and the need to see over the tall grass.

The upwelling of rocky terrain, replacing the forest of East Africa about 3.5 to 4 million years ago forced our ancestors out of the disappearing trees.

The need for safety forced us to walk upright. This allowed for the extension of the laryngeal organ, allowing for more complex grunts and howls eventually leading to the ability for rudimentary speech.

A good example of this prehistoric speech would be our illustrious President for Life, Idi Amim DaDa Bush.

Answer 7

[edit] Humans

Main article: Human skeletal changes due to bipedalism

There are at least twelve distinct hypotheses as to how and why bipedalism evolved in humans, and also some debate as to when. 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.

Humans evolved from a chimpanzee-like, knuckle-walking ancestor. Various reasons have been proposed for the evolution of human bipedalism, including freeing the hands for tool use and carrying, sexual dimorphism in food gathering, changes in climate and habitat (from jungle to savanna) and to reduce the amount of skin exposed to the tropical sun. The first two explanations have been criticized for projecting modern social concerns and prejudices onto ancestral species. The latter two have been criticized for not making sense in the context of the forest and woodland biomes occupied by human ancestors. An alternative explanation is the mixture of savanna and scattered woods forced proto-humans to travel between clusters of trees and bipedalism offered greater efficiency for slow, long-distance travel between these clusters than knuckle-walking quadrupedism.[17]

[edit] Postural feeding hypothesis

The postural feeding hypothesis has been recently supported by Dr. Kevin Hunt, a professor at Indiana University. This theory asserts that chimpanzees were only bipedal when they ate. While on the ground, they would reach up for fruit hanging from small trees and while in trees, bipedalism was utilized by grabbing for an overhead branch. These bipedal movements may have evolved into regular habits because they were so convenient in obtaining food. Also, Hunt theorizes that these movements coevolved with chimpanzee arm-hanging, as this movement was very effective and efficient in harvesting food. When analyzing fossil anatomy, Australopithecus afarensis has very similar features of the hand and shoulder to the chimpanzee, which indicates hanging arms. Also, the Australopithecus hip and hind limb very clearly indicate bipedalism, but these fossils also indicate very inefficient locomotive movement when compared to humans. For this reason, Hunt argues that bipedalism evolved more as a terrestrial feeding posture than as a walking posture. As Hunt says, “A bipedal postural feeding adaptation may have been a preadaptation for the fully realized locomotor bipedalism apparent in Homo erectus.” A related hypothesis is that proto-humans learned upright posture not for picking fruit, as it is argued they would have stayed climbers if plucking fruit were all they were after, rather they learned to keep their head out of the water while searching for water plants, mollusca, and the like.

[edit] Provisioning model

One of the most elaborate theories on the origin of bipedalism is the behavioral model presented by C. Owen Lovejoy, which is known as "male provisioning".[18] Lovejoy theorizes that the evolution of bipedalism was a response to a monogamous society. As hominid males became monogamous, they would leave their families for the day in order to search for food. Once they found food for their family, the hominids would have to bring back the food, and the most effective way of doing this was through bipedalism.

There is some question over whether or not early hominids were monogamous. Some evidence indicates that early hominids, which were proven to be bipedal, were in fact polygamous. Among all monogamous primates, sexual dimorphism is greatly decreased. In Australopithecus afarensis, males were found to be nearly twice the weight of females (as well as a great deal taller), an attribute scientists would expect[citation needed] in a polygamous species. Lastly, monogamous primates are highly territorial, but fossil evidence indicates that Australopithecus afarensis lived in large groups. Overall, there is no concrete evidence to thoroughly discount or prove monogamy or polygamy in early hominids.

[edit] 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.

[edit] Thermoregulatory model

The thermoregulatory model explaining the origin of bipedalism is one of the simplest and most fanciful theories on the table, but it is a viable explanation. Dr. Peter Wheeler, a professor of evolutionary biology, proposes that bipedalism raises the amount of body surface area higher above the ground which results in a reduction in heat gain and helps heat dissipation. When a hominid is higher above the ground, the organism accesses more favorable wind speeds and temperatures. During heat seasons, greater wind flow results in a higher heat loss, which makes the organism more comfortable. Also, Wheeler explains that a vertical posture minimizes the direct exposure to the sun whereas quadrupedalism exposes more of the body to direct exposure.

[edit] Carrying models

Charles Darwin wrote that "Man could not have attained his present dominant position in the world without the use of his hands, which are so admirably adapted to the act of obedience of his will" Darwin (1871:52) and many models on bipedal origins are based on this line of thought. Gordon Hewes (1961) suggested that the carrying of meat "over considerable distances" (Hewes 1961:689) was the key factor. Isaac (1978) and Sinclair et al (1986) offered modifications of this idea as indeed did Lovejoy (1981) with his 'provisioning model' described above. Others, such as Nancy Tanner (1981) have suggested that infant carrying was key, whilst others have suggested stone tools and weapons drove the change.

[edit] Wading hypothesis

Main article: Aquatic ape hypothesis

The Aquatic ape hypothesis proposes that humans evolved bipedalism as a result of bipedal wading. Mammals that switch from quadrupedalism on land to bipedal wading appear mainly to be found among large primates, especially apes, with relatively few exceptions such as the grizzly bear. Bipedal wading has been observed in the bonobo, chimpanzee, lowland gorilla, orangutan, baboon and proboscis monkey. Bipedal wading provides the advantage of keeping the head above water for breathing.

[edit] Savannah hypothesis

This proposes that the onset of drier conditions severely reduced the amount of wooded habitats. During this period, when the forests became thin, early hominids adapted to an environment which was now more like the liminal forest-savanna mosaic zones of equatorial Africa. In order to remain effective in gathering food, the hominids had to travel relatively long distances with food or tools, thus making quadrupedalism extremely inefficient. Bipedalism developed both as an adaptation to facilitate movement across the grasslands and as a way to give early hominids use of their hands for food cultivation and tool use since they were no longer needed for locomotion