I am posting a second topic on this subject since the first one became overrun by snakes.
Cofty posted a link to a published paper discussing this topic and referred to the information in it as "facts". Here is my summary of that paper along with comments on it.
One of the opening statements says that:
Two frequently debated aspects of hominin evolution are the development of upright bipedal stance and reduction in body hair.
So for those who believe this is a stupid topic, it is a subject of interest to many stupid people including the authors of the paper referred to by Cofty. This paper proposes a new model for development of these features based on thermoregulation. Their new model assumes a high level of activity which alters the heat balance calculations proposed by previous authors. The graphs appearing below show the predictions of their model for "the amount of heat that must be dissipated by sources other than normal respiration (such as sweating) to maintain heat balance, as a function of time of day". The top graph is for females in the bottom graph for males. As stated in the legend the relatively straight lines the graphs are for hairy or fur covered animals and the two arcing lines are for hairless quadrupeds and bipeds respectively.
These authors do not come to any conclusions regarding the subject of bipedalism as far as timing or cause stating:
All their model does is predict that there would be a thermoregulatory advantage near dusk and dawn for highly active hairless creatures that were simultaneously losing their fur and acquiring a greater ability to sweat. These two changes continued to develop in tandem until humans didn't have fur and were extremely good at sweating at which point humans could run around for longer time in hot sunny conditions. This is the "answer" to my question and is referred to by Cofty as "facts".If both of these changes occurred primarily through thermoregulatory evolutionary pressures, then we predict that hair loss would occur before bipedalism. However, if physical evidence suggests a different relative timing, then this would suggest that the initial evolution of bipedalism was not driven by thermoregulatory selection pressures. . . .
So currently it appears that upright stance may have evolved earlier than hair loss; however, such a conclusion must be very tentative.
Specifically, we postulate progressive hair loss being selected and this allowing individuals to be active in hot, open environments initially around dusk and dawn without overheating. Then, as our ancestors’ hair loss increased and sweating ability improved over evolutionary time, the fraction of the day when they could remain active in such environments extended. Our model suggests that only when hair loss and sweating ability reach near-modern human levels could hominins have been active in the heat of the day in hot, open environments.
Dr. Nina Jablonski added that a third factor would have had to occur along with development of fur loss and sweating ability which is not mentioned in this paper. link
Specifically, we postulate progressive hair loss being selected and this allowing individuals to be active in hot, open environments initially around dusk and dawn without overheating. Then, as our ancestors’ hair loss increased and sweating ability improved over evolutionary time, the fraction of the day when they could remain active in such environments extended. Our model suggests that only when hair loss and sweating ability reach near-modern human levels could hominins have been active in the heat of the day in hot, open environments.
Dr. Rantala shot holes in this proposed model back in 2007: Rantala
The cooling device hypothesisRantala lists twelve different explanations offered by evolutionary scientists for the loss of fur and pokes holes in all of them except for the one he favors. In my opinion it is clear that there is no explanation for this situation and to cite one theory and refer to it as the "facts" is highly disingenuous. In my mind it calls into question all of the topics posted on the subject of evolution.
Perhaps the most commonly held explanation for the evolution of the nakedness in humans is that it evolved as a cooling device (e.g. Morris, 1967; Leakey & Lewin, 1977; Mount, 1979; Ebling, 1985). It has commonly been thought that by abandoning the shady forest, the hunting ape exposed himself to much higher temperatures than those to which he had previously adapted. Thus, it has been assumed that the hunting ape took off his hairy coat to avoid becoming overheated in the hot savannah (Morris, 1967).
Unfortunately, this hypothesis does not bear closer scrutiny. When we compare the thermal budgets of haired and naked hominids (Wheeler, 1992b), we can easily see that a naked skin is a disadvantage with regard to the circadian integral over both day time (it receives more solar energy, requiring dissipation) and night-time (it requires more endogenous heat production) (Amaral, 1996). Exposure of the naked skin to the air certainly increases the chances of heat loss, but at the same time it also increases heat gain and risks damage from the sun’s rays. Thus, it increases perspiration, leading to dehydration; this in turn may be detrimental in a dry savannah environment. A haired hominid in an open hot environment should actually increase its insulation rather than decrease it. This is precisely the trend followed by savannah monkeys, which have a dense hair-coat and are better insulated than forest primates (Mahoney, 1980).
- The cooling device hypothesis
- The hunting hypothesis
- The bipedality hypothesis
- The allometry hypothesis
- The clothing hypothesis
- The vestiary hypothesis
- Neoteny hypothesis
- Carrion-eating hypothesis
- Sex-related hypothesis
- Aquatic ape hypothesis
- Adaptation-against-ectoparasites hypothesis
- Darwin’s hypothesis
One point shared in common by all 12 theories is that humans have no fur due to an evolutionary process. Once creation is ruled out then all sorts of flights of imagination can occur.
