Evolution, eyebrows and strong brow-ridges

[Bryce]

Here is a question I submitted on an "ask-a-scientist" website, without getting an answer for the while.
"Why did evolution favor eyebrows in replacement of visor-like brow ridges?". Additional comments :
If nature selected the emergence of these hairy patches called eyebrows in order to offer our eyes extra shade and keep sweat from trickling into them, why did it erase in the first place the supra-orbital torus or even strong projecting hairless brow-ridges? Is it an example of evolutionary error followed by its correction? Is it reasonable to think that people with very sparse or inexistent eyebrows (and they are not rare at all) display an archaic trait? On the other hand, having exceptionally projecting brow-ridges seems to be only seen in pathological conditions such acromegaly.
It makes one wonder...

[Drooperdoo]

Bryce, your comment about the disappearance of the large Neanderthal frontal lobe in the human race is a fascinating one. While I have no idea why Nature replaced man's frontal lobe with the ingenious invention of eyebrows, I *do* have an observation of my own: It might be a symptom of a larger phenomenon. That is to say, with each advance in evolution, Nature tends to favor infantilism over senility. Babies, for instance, absorb information at a far greater rate than adults. To create a smarter species, it is in the best interests of the animal to retain this infantile ability to learn more, to absorb information faster--and to keep this ability until a far greater age. So Nature encourages this sort of infantilism in Man. Many anthropolgists have noted that Homo sapiens displays infantile traits that appear in the chimp but then disappear when the ape reaches maturity. So, in other words, Man is an ape that has developed a prolonged adolescence.
Having a smaller frontal lobe is an example of this.
Following this logic, one sees infantile traits among the races of mankind. The sub-Saharan Africans are the oldest genetic group of mankind. The next-oldest are the Caucasians. Unlike the Africans, the Caucasians retained infantile traits into adulthood: Like blue eyes (which many babies have but which disappear upon maturity). The whites retain this "infantile trait" into adulthood. Likewise, the most recent race [the Mongoloid] has even more infantile traits: The epicanthic fold over the eyes [which appears in most babies but disappears soon enough]. Yet, in the Asians, this "infantile trait" remains, as do other body-features: Shortness of stature, greater mental elasticity which results in higher IQ's, etc.
This phenomenon has been observed in geniuses of all racial stripes, as well: They tend to be child-like . . . or in Mozart's case "childISH". These men of superior intellect seem to be caught in a prolonged adolescence--a superannuated childhood--and, as a result, their minds remain as absorbant as a baby's. Picasso, Einstein, Beethoven: All short men with childlike physiques and big brains.
It's in Nature's best interests to prolong infantile traits--hence the Homo sapiens' remarkable resemblance to the adolscent Neanderthal and the disappearance of the giant frontal lobe in favor of a less "mature," simian skull-shape.

[SensoUnico]

Interesting hypothesis. What if it was the other way round? The races with the most neoteny are the oldest. The least neotenous are the youngest. Australoids are an old race and there are neotenous groups among them. Mongoloids are neotenous as a whole. Caucasoids as you said retain baby characteristics into adulthood such as blue eyes and to a lesser extent light hair. In Africa, pygmies are more of a severe adaptation to a limited environment in the way elephants stranded on Mediterranean islands became smaller over time and eventually extinct. Bushmen are truly neotenous. But are they negroid? I think not myself. I think negroids are the youngest race. What is your opinion?

[mike2]

gundagai said:

But are they negroid? I think not myself. I think negroids are the youngest race. What is your opinion?

You're right, the Bushmen are not negroid. They're Capoid, a race apart. Many people also share your opinion that the Negroes are a young race.

[kiengi]

Out of africa theory is confirmed, but also a theory that N. Asians sometime later migrated back to Africa when global climate became colder. Bushman with eyelid fold suggest they might be originated from N. Asia.

[human2]

kiengi said:

Out of africa theory is confirmed, but also a theory that N. Asians sometime later migrated back to Africa when global climate became colder. Bushman with eyelid fold suggest they might be originated from N. Asia.

Actually, Bushmen are genetically the "oldest" population not just in Africa but in the world.
What are you basing this on? It's rather dumb.

gundagai said:

Interesting hypothesis. What if it was the other way round? The races with the most neoteny are the oldest. The least neotenous are the youngest. Australoids are an old race and there are neotenous groups among them. Mongoloids are neotenous as a whole. Caucasoids as you said retain baby characteristics into adulthood such as blue eyes and to a lesser extent light hair. In Africa, pygmies are more of a severe adaptation to a limited environment in the way elephants stranded on Mediterranean islands became smaller over time and eventually extinct. Bushmen are truly neotenous. But are they negroid? I think not myself. I think negroids are the youngest race. What is your opinion?

It's been the general trend for humans, moderns included, to develope more neoteny. Much of the reasons why moderns skulls look more modern/delicate is actually because of neoteny.

There is also a difference, I think, between neoteny (the retainment of childhood features into adulthood) and pademorphia (the cessation of growth in the teens as one ages into adulthood).

According to Nature magazine, Negritos and pygmies stop growth around their teens, as seen from their skulls and size. I think this is different from neoteny, where growth doesn't stop but it's more of a case of retainment of certain childish features as you grow.

This is different from the retainment of child-like features while fully growing into adults, I think.

The Bushmen might be a case of both. The eyes and malars seem to be a case of neoteny while some of the shape of the skull (big foreheads, weak chin, bopdy size) indicate arrrested development during teens.
The Bushmen are the oldest genetic population but that doesn't mean they always looked that way. In fact the skull finds of moderns before 20,000 are all rather "rough" and non-neotenic.

[Drooperdoo]

Interesting comments in here: As for me, I've heard quite the opposite [about Australian aborigines]. According to everything I've read, they aren't genetically old at all. They branched off from Asians, who branched off from Caucasians. The oldest race--according to current methods of gene-dating--are the sub-Saharan Africans. According to Cavalli-Sforza's work, the two furthest genetic groups are sub-Saharan Africans and Austroloids.
As to the theory of "old race" = "mature physical traits," any forensic anthropologist can attest that black Africans have the smallest crania-to-body-height ratio. This makes sense since they're the oldest race. Next come Caucasians, who have much larger skulls. Then--if we believe genetic dating--Orientals branched off of Caucasians and have even larger heads. Indeed, Asian skull-measurements are about equal with Caucasians--but when we consider that they are on average several inches shorter, than we see that the skull-size-to-height ratio is increasing with every new "race". Infantile traits supplanting "adult" traits as the species continues to re-invent itself.
The famous author H.G. Wells--who held his degree in biology--had a chapter in his last work "The Mind At the End of Its Tether" and a section entitled "Race Suicide by Gigantism". In this section he observes that at the end of every species' history, the animal in question gets large--right before extinction. This was true of dinaosaurs, birds, aquatic life, etc.
It's fascinating that when the Spaniards first decided to take sub-Saharan Africans as slaves they did so because this oldest race was also the tallest. Spaniards--as Europeans--were next in height; and Aztecs (as one of the world's youngest races) were by far the shortest. In other words, as each race ages it seems to get taller. I find this fascinating because European height is increasing. Some attribute it to coincidence, some to diet, others to more murky factors. But--if one follows H.G. Wells' hypothesis about "race suicide by gigantism," it falls right into the pattern: Within a hundred years, the Dutch went from Europe's shortest country to the world's tallest. And the same is true of most other Caucasoid groups: We're getting bigger--joining the Africans as the world's six-footers--as the younger races develop infantile traits . . . short statures, epicanthic folds, large skull-to-height ratios, etc.
So I find it amusing that as we Westerners get taller we assume its some sign of superiority, of vitality--when in fact (just as with the dinaosaurs) its an indication that the end is near . . . as the smaller and leaner mammals scurry about in the grass--the unimposing heirs of the future.

[SensoUnico]

I don't consider the Out of Africa theory proved beyond reasonable doubt. I have studied Australoids for a long time and the group is very old going back to 60000 years in Australia alone. The point about pedomorphism and neoteny is good. I differ in that the pygmies of Africa are not neotenous or pedomorphic. They are just small humans with the consequent exaggeration of West African negro features that arises from stunting. If you selectively breed caucasoid dwarves in Nebraska you would end up with the caucasoid equivalent of pygmies. Negritos as in the Phillippines are definitely pedomorphic and neotenous. Australian Aborigines are composed of three types of Australoids. Among Australian Aborigines the "pygmatoid" Aborigines of North Queensland are both pedomorphic and neotenous in comparison with typical Aborigines such as the Pintubi. The current accepted beliefs is that SSAs are the oldest humans. I don't see the evidence the same way as Cavalli-Sforza. I do not share his paradigm or biases. Africa is a big land mass with different races like the Sanids, Negrids, Ethiopids, Caucasians and it is very understandable that these races would vary genetically. I know SSA is a euphemism for negroid but most of Africa is sub saharan and that includes all the main races of Africa and their mixes. A lot of evidence is based on mtDNA and assumptions about mutation rates and what is older. mtDNA is labelled as such as it is not really human DNA or eukaryotic DNA being in reality a bacterium which infested eukaryotic cells millions of years ago and became mutually dependent on the eukaryotic cell. Frankly my female ancestress was a human being not a bacteria. mtDNA is an indicator and what it indicates is subject to interpretation.

[Bryce]

As I answered to one of the members who commented my post in a private message, I had not designed my question under the angle of neoteny, but rather as a question about the "try-and-fail / try-and-succeed" way that nature has to select distinctive traits. Nevertheless, the neotenic approach may well be valid.

[kiengi]

human2 said:

Actually, Bushmen are genetically the "oldest" population not just in Africa but in the world.
What are you basing this on? It's rather dumb.

Well, population genetics is just my passing interest at the moment, and am a least bit of an expert. But..

I read that, Khoisan gene pool of S.E. Africa region has M173 mutations, signals Asian origin, therefore back migration. That is, if out of Africa theory holds.

Other possibilities are, may be Chinese migrated there long time ago.

[human2]

kiengi said:

Well, population genetics is just my passing interest at the moment, and am a least bit of an expert. But..

I read that, Khoisan gene pool of S.E. Africa region has M173 mutations, signals Asian origin, therefore back migration. That is, if out of Africa theory holds.

Other possibilities are, may be Chinese migrated there long time ago.

M173 is R, which is associated with basically Europe. It's actually the predecessor of R1a/M73, which people think is proto-Indo-European. (Also, you just said M173 is European in dodona.proboards35.com/index.cgi?action=display&board=physanth&thread=1109223335&start=75

As for M173 in Khoisan, you've proven to be unreliable. Can't even get your facts right.

[nockwasright]

Drooperdoo said:

Interesting comments in here: As for me, I've heard quite the opposite [about Australian aborigines]. According to everything I've read, they aren't genetically old at all. They branched off from Asians, who branched off from Caucasians. The oldest race--according to current methods of gene-dating--are the sub-Saharan Africans. According to Cavalli-Sforza's work, the two furthest genetic groups are sub-Saharan Africans and Austroloids.
As to the theory of "old race" = "mature physical traits," any forensic anthropologist can attest that black Africans have the smallest crania-to-body-height ratio. This makes sense since they're the oldest race. Next come Caucasians, who have much larger skulls. Then--if we believe genetic dating--Orientals branched off of Caucasians and have even larger heads. Indeed, Asian skull-measurements are about equal with Caucasians--but when we consider that they are on average several inches shorter, than we see that the skull-size-to-height ratio is increasing with every new "race". Infantile traits supplanting "adult" traits as the species continues to re-invent itself.
The famous author H.G. Wells--who held his degree in biology--had a chapter in his last work "The Mind At the End of Its Tether" and a section entitled "Race Suicide by Gigantism". In this section he observes that at the end of every species' history, the animal in question gets large--right before extinction. This was true of dinaosaurs, birds, aquatic life, etc.
It's fascinating that when the Spaniards first decided to take sub-Saharan Africans as slaves they did so because this oldest race was also the tallest. Spaniards--as Europeans--were next in height; and Aztecs (as one of the world's youngest races) were by far the shortest. In other words, as each race ages it seems to get taller. I find this fascinating because European height is increasing. Some attribute it to coincidence, some to diet, others to more murky factors. But--if one follows H.G. Wells' hypothesis about "race suicide by gigantism," it falls right into the pattern: Within a hundred years, the Dutch went from Europe's shortest country to the world's tallest. And the same is true of most other Caucasoid groups: We're getting bigger--joining the Africans as the world's six-footers--as the younger races develop infantile traits . . . short statures, epicanthic folds, large skull-to-height ratios, etc.
So I find it amusing that as we Westerners get taller we assume its some sign of superiority, of vitality--when in fact (just as with the dinaosaurs) its an indication that the end is near . . . as the smaller and leaner mammals scurry about in the grass--the unimposing heirs of the future.

I don't see the pattern. Gigantism of dinosaurs (in the gigantism hypotesys) was due to sexual (and internal) selection and then proved to be a problem due to change of environment. Doesn't seem to be the same with humans. Also newest "race" means only group that isolated itself from the others later, it does not mean "more evolved". Finally, Austraoloids should be even "newer" than Mongoloids but they're not neotenic nor short.

[human2]

"Australoids" are not "newer" than "Mongoloids". Most of the early moderns found all over the world are of this type. Australia is also one of the first regions reached, right after India and SE Asia, and before northern Asia and Europe, if the genetics and paleontology is to be believed.

This makes sense since it's a hot coastal environment and early moderns didn't have to make lifestyle changes as they headed out of Africa along the coast, so they chose that route first.

There is no selection pressures in the tropics (no great fluctuations in environment that increase and decrease population size at will). The only way phenotype changes is because of selection pressures.

There was no selection pressures in Australian aborigines as well as Indian aborigines and they stayed true to the original look of moderns at the time.

[nockwasright]

human2 said:

"Australoids" are not "newer" than "Mongoloids".

Ok I thought they "branched off" later as I thought they are the fartest group from SSA. My knowledge of the subject is really skindeep so I may well be wrong.

This however doesn't save the gigantism theory IMO.

[kiengi]

human2 said:

M173 is R, which is associated with basically Europe. It's actually the predecessor of R1a/M73, which people think is proto-Indo-European. (Also, you just said M173 is European in dodona.proboards35.com/index.cgi?action=display&board=physanth&thread=1109223335&start=75

As for M173 in Khoisan, you've proven to be unreliable. Can't even get your facts right.

Full linage as i read in yr 2002 research paper:

M45->DYS257->M207->M173->M117,117b

Northern Europe was humanly un-inhabitable due to ice sheets up until 10K yrs ago. M173 is european roots that was in Asia at the time.

if you have any authority in this field to correct mistakes in some past group research results then please do so. I am just passing by.

I have no need to post something false on this board, as i do not want others to do the same.