|
Post by Agrippa on Mar 29, 2005 20:51:05 GMT -5
If you mean Negritids which is the only type of the wider Australoid group which is rather paedomorphic, this is secondary specialisation imo
Furthermore its not the same being genetically an older branch and being archemorphic-primitive since some of the older populations (f.e. Khoisanids) evolved on in a certain direction (f.e. get smaller and somewhat more infantilised because they were displaced and driven in regions were they live in small groups and with low energy) whereas some newer groups like the Australids or some Indianid groups (Fuegide f.e.) kept in there rather isolated region older features which were extinct elsewhere.
Saying that where you find the most archaic features today means this populations are "so old" is like saying lemurs in Madagaskar or the platypus in Australia are older. They just didnt evolved on, they kept a form which was, at least a similar one, much more widespread. Same for Australids, they kept all the primitive-archaic features just because they were isolated and had no strong selective pressure to evolve on in another direction than the classical sapiens stratum already had.
If its about the browridges, it depends on more than one factor, but yes, weaker browridges might have been favoured by sexual selection and not too forget that the general robustness of sapiens is much weaker compared to Neandertals. More robust-masculine individuals tend to have stronger browridges usually...
Furthermore eyebrows were most likely nothing which replaced the strong browridges, but were there even in individuals which had strong browridges imho. The advantage is just too big, even on the contrary, I think that the eyebrows are weaker in moderns because of sexual selection...
|
|
|
Post by SensoUnico on Mar 30, 2005 9:02:08 GMT -5
Yes I mean negritids but not exclusively. Some melanesians are small statured and reduced in form. The Australian Aborigines in parts of North Queensland are small statured, and with child like features when compared to other typical Aborigines. The Vedda of Sri Lanka were reduced. Aborigines and negritids are not all the Australoids. The Australoid groups in SE Asia have mostly been absorbed by Malay type people. The Australian Aborigines are both archaic and old. Australia was for them an evolutionary dead end. It is interesting that the Aboriginal physical characteristics disappear very quickly by mixing with caucasians unlike negroid features which are more persistent.
|
|
Bryce
Full Member
Posts: 206
|
Post by Bryce on Apr 9, 2005 8:15:40 GMT -5
Your attention, everybody, here is the answer to my original question I got from Professor Mark Spencer, Arizona State University : "The supraorbital torus, or browridge, is variably present in several species of primates, and is very prominently displayed in some apes and Pleistocene hominids. It is essentially absent in orangutans, and is very weakly developed in most early hominids, such as the australopithecines. This pattern does not appear to have any obvious relationship to some need for shade or protection from sweat (which is pronounced only in humans), and the idea that this is the role that the browridge plays is simply not accepted within physical anthropology any longer. It never was very seriously considered, in fact. A more common idea has been that the browridge serves as a boney buttress in the upper face to assist in resisting the stresses produced during chewing, but this idea is also out of favor (experimental work on macaques using strain gages to measure the strains in the supraorbital region during feeding showed that the structure simple isn't stressed very much). The prevailing hypothesis currently is that browridge presence is related to the spatial positioning of the eye orbits and the brain case. When the orbits are positioned far forward of the frontal lobe of the brain, there is a shelf of bone covering them that probably serves to protect the orbit contents (the eyes) from blows. When the orbit is tucked in under the brain, however, there is no need for this shelf (the brain and brain case protect the orbits), and we see none. This hypothesis is consistent with measurements of orbit and brain positioning in old world monkeys, but has not been examined beyond this group. So, eyebrows and browridges are not functionally equivalent, and the prominence of hairy eyebrows in living humans is therefore unlikely to be a solution to some problem posed by the loss of browridges. As for the adaptive significance of eyebrows, it is reasonable to hypothesize that they protect the eyes from glare and the excessive sweat modern humans produce. But this is only an hypothesis until it is tested in some way. The idea that individuals who have sparse eyebrows are in some way displaying the ancestral condition is unlikely – most traits in humans display a range of variation."
|
|