How did all racial physical differences come about?

[bombus]

Ok you guys said skin pigment was effected by the climate and amount of sunlight, which makes sense, except for the eskimos...Why do they have dark skin and the Europeans in the cold climate developed lighter skin?

 

Eskimos also eat lots of fish - very high in Vitamin D. Thus no need to develop pale skin. Also, increased sunlight due to reflection from snow and ice may make darker skin advantageous.

 

No worries, I had an advantage. I was born there (makes it easier to remember). These are Turkana. That's me, bottom left at the front.

 

Neat! Great photo!

[JHAQ]

Incipient speciation ---

[lucaspa]

Also, increased sunlight due to reflection from snow and ice may make darker skin advantageous.s

 

That isn't going to change the amount of UV radiation.

 

Incipient speciation ---

 

I haven't seen any studies on incipient speciation involving Inuits. However, there are indications if incipient speciation in the !Kung. There is very limited gene flow there and it flows only one way: out of the !Kung. When !Kung mate outside the tribe, they must leave and live with the spouse's people.

 

There are studies indicating that the !Kung have several unique alleles in the population and, if the movie The Gods Must Be Crazy is accurate, neither Europeans nor !Kung view the other as desirable mates -- an early sign of reproductive isolation.

[insane_alien]

That isn't going to change the amount of UV radiation.

 

not overall but it will increase the UV radiation that happens to hit the person. as they will get both direct UV from the sun and indirect UV from the snow.

[waitforufo]

I agree with the comments on climate and its effect on evolution, but don’t neglect sexual attractiveness. For example, I saw a nature program where they discussed male peacocks. There is not much about the physical properties of male peacocks that make sense from the survival standpoint. By that I mean not getting eaten by predators. The physical properties of male peacocks that make them most attractive to female peacocks also make them poor at flying, running, being seen, and otherwise evading predators. But they do mate more.

 

The same I am sure is true to some degree with humans. If fair skin becomes “fashionable”, for lack of a better word, fair skinned people will mate more often. Currently, most glamour magazines select models from all races based on fairness of skin. Light skinned models are preferred. This could have a tendency to increase the sexual attractiveness of light skinned people thereby increasing the mating possibilities of fair skinned people of all races. This could move the entire human species in the direction of fairer skin. The same would be true for any physical characteristic and long as the attractiveness pervades for a long enough period of time. I would imagine that this type of selection would also work faster than a more random natural selection process based on climate. We are in effect selectively breeding ourselves.

[bombus]

That isn't going to change the amount of UV radiation.

 

Mmm, tell that to a surfer, fisherman, skier or sailor. Reflection of sunlight from snow or water can cause sunburn.

 

I agree with the comments on climate and its effect on evolution, but don’t neglect sexual attractiveness. For example, I saw a nature program where they discussed male peacocks. There is not much about the physical properties of male peacocks that make sense from the survival standpoint. By that I mean not getting eaten by predators. The physical properties of male peacocks that make them most attractive to female peacocks also make them poor at flying, running, being seen, and otherwise evading predators. But they do mate more.

 

The same I am sure is true to some degree with humans. If fair skin becomes “fashionable”, for lack of a better word, fair skinned people will mate more often. Currently, most glamour magazines select models from all races based on fairness of skin. Light skinned models are preferred. This could have a tendency to increase the sexual attractiveness of light skinned people thereby increasing the mating possibilities of fair skinned people of all races. This could move the entire human species in the direction of fairer skin. The same would be true for any physical characteristic and long as the attractiveness pervades for a long enough period of time. I would imagine that this type of selection would also work faster than a more random natural selection process based on climate. We are in effect selectively breeding ourselves.

 

Have you read 'the red queen' by Matt Ridley? Great book all about this. It has major implications on how we view the process of natural selection.

[lucaspa]

not overall but it will increase the UV radiation that happens to hit the person. as they will get both direct UV from the sun and indirect UV from the snow.

 

When you are all wrapped up in furs due to the cold, what difference does it make? BTW, are you sure UV is reflected off of ice? You might find that water absorbs light at the UV wavelengths -- most compounds do.

 

I agree with the comments on climate and its effect on evolution, but don’t neglect sexual attractiveness. For example, I saw a nature program where they discussed male peacocks. There is not much about the physical properties of male peacocks that make sense from the survival standpoint. By that I mean not getting eaten by predators. The physical properties of male peacocks that make them most attractive to female peacocks also make them poor at flying, running, being seen, and otherwise evading predators. But they do mate more.

 

You have three points here:

 

1. Sexual selection. Yes, sexual selection happens and, in fact, it is a new hypothesis put forward to explain hairlessness in humans. About the time of H. erectus (long before the skin color change we are talking about) it is hypothesized that hairlessness in both males and females became a selective trait.

 

2. Sexual selection is often tied to adaptive traits. That is, the peacock's tail appears to be maladaptive and would pose a hindrance for them to escape predators. However, in reality, other genes that are adapted are tied to the genes for the tail.

 

3. Skin color may have been more sexual selection than adaptive. We have the data on the adaptiveness of skin color vs UV radiation -- both for folic acid preservation and production of vitamin D. Skin color correlates well with latitude around the globe. So there are 2 independent lines of data supporting the hypothesis. What data have you seen supporting that skin color is sexually selective?

 

The recent glamour magazines don't count because this type of pressure wasn't around 100,000 - 20,000 years ago when the evolution of skin color was happening. That fair skin is thought to be desirable today can be attributed to the dominance of Western European/American culture.

 

This could have a tendency to increase the sexual attractiveness of light skinned people thereby increasing the mating possibilities of fair skinned people of all races. This could move the entire human species in the direction of fairer skin.

 

Could, but unlikely. The entire human species right now is 6 billion people and nearly all of them find mates and reproduce. This makes for 1) a great deal of inertia in shifting the bell-shaped curve of skin color and 2) doesn't really result in differential reproduction. After all, if men (or women) settle for their 2nd or 3rd choice of mate and still mate with a person of darker skin color and have children, the frequency of alleles doesn't change. You might get wealthier people picking mates of lighter skin color, but it is well-documented that wealthy people have LESS children than poor. So that would mean shifting the curve toward darker skin color, since the lighter skinned people will have less children.

 

I would imagine that this type of selection would also work faster than a more random natural selection process based on climate.

 

Your premise of a "random natural selection process" is mistaken. Natural selection is NOT "random". It is very deterministic. Therefore it works faster, usually, than sexual selection which is, as you noted, often fickle. However, the amount of average sunlight at different latitudes is constant generation after generation. Also consider that a light skinned woman born in Africa in a primitive society is not going to have ANY living kids -- because they all die from spina bifida shortly after birth. Similarly, a dark skinned person born above 50 degrees latitude is going to die before they even get to be teenagers -- from rickets. That is a hugely more effective selection pressure than mate selection -- especially in a society where everyone gets a mate.

 

To illustrate the fickleness of sexual selection in humans, if you go back just 500 years, you find that the ideal woman was plump. Look at the women painted by the Rennaisance painters -- who were, after all, painting what they considered attractive women (just like artists today). In just 500 years the concept of attractiveness in women has done a 180 -- now it is thin women that are considered attractive and desirable.

[Paralith]

2. Sexual selection is often tied to adaptive traits. That is, the peacock's tail appears to be maladaptive and would pose a hindrance for them to escape predators. However, in reality, other genes that are adapted are tied to the genes for the tail.

 

Often, but not always. The tail is still going to be an escape hindrance compared to other males with smaller tails. A trait need not necessarily be linked to an adaptive one in order to be sexually selected for. It's called the "sexy sons" theory. A female wants to mate with a particularly attractive male so that her sons, in turn, will be particularly attractive and mate often. The males, in turn, experience conflicting selective forces between predators and females. There are various ways that this preference can develop, but it doesn't have to be linked to environmental adaptations. But, it often is. In the case of birds, only strong and healthy males have the resources to grow and maintain bright and colorful plumage, for example. In other cases, a good gene might simply be passed down with a gene for large tails just through chromosomal linkage.

[waitforufo]

Lucaspa,

Your post 32 is excellent. In my post (30) I wasn’t trying to claim expertise in the subject, I was just trying to introduce the concept. Previous posts only mentioned climate as a driver for racial diversity. As I said, “I saw a program …” and that program is the full extent of my expertise on the subject. If you read my post (30) again, you will also find “The same, I am sure is true to some degree with humans.” The degree to which sexual attractiveness has influenced human diversity is a mystery to me. It seems logical however, that it has had some influence.

[bombus]

When you are all wrapped up in furs due to the cold, what difference does it make? BTW, are you sure UV is reflected off of ice? You might find that water absorbs light at the UV wavelengths -- most compounds do.

 

The genes maybe didn't give the option of having dark faces and hands with pale bodies, but there could be many other factors involved that are nothing to do with the current environment where 'eskimos' live.

 

I also thought that UV would not be reflected, but in my experience it can.

[lucaspa]

Often, but not always.

 

I hate to be picky, but what did I say? You quoted it: "2. Sexual selection is often tied to adaptive traits."

 

Yes, the tail itself is maladaptive, but it is more than compensated for by other adaptive traits. An extensive study was done in frogs:

3. E Pennisi, Females pick good genes in frogs, flies. Science 280:1837-1838, (19 June) 1998. Discusses recent studies that show how "bad" genes associated with male display are actually connected to survival genes in males, so that females actually pick survival traits. In frogs the descendents of "long callers" did better in every fitness test.

 

A trait need not necessarily be linked to an adaptive one in order to be sexually selected for.

 

I never said it did. However, as more and more of these studies are done, it is turning out that "maladaptive" traits that are sexually selected for are linked to adaptive traits.

 

In other cases, a good gene might simply be passed down with a gene for large tails just through chromosomal linkage.

 

And here is the start of linkage. This means that females picking the mate because of the large tail are also going to get a mate with another adaptive trait -- and have more surviving kids. So now sexual selection is also natural selection. Yes, on the surface the females are picking mates based on sexual cues -- sexual selection -- but underneath natural selection is also at work.

 

The genes maybe didn't give the option of having dark faces and hands with pale bodies, but there could be many other factors involved that are nothing to do with the current environment where 'eskimos' live.

 

Yes, it appears that pigmentation in humans is not able to be completely segregated (remember, most of the faces and hands also have to be covered in winter when there is snow to reflect sunlight). Having the darker areas exposed to UV still means that they are not getting enough vitamin D thru exposure to sunlight.

 

BUT, there are 2 other factors at work:

1. Vitamin D thru the diet. Traditional Inuits eat the livers of whales and seals.

2. Insufficient generations to evolve paler skin. Remember, Inuits could only migrate to the region about 12,000 years ago when the glaciers melted at the end of the last Ice Age. Until then, they lived at a lower latitude and warmer climates. So, they are descended from darker skinned ancestors (Asians) and haven't been in the current location long enough.

 

Lucaspa,

Your post 32 is excellent. In my post (30) I wasn’t trying to claim expertise in the subject, I was just trying to introduce the concept.

 

That's fine, but what I want you to do is test your introductions before you post them. Your "introduction" was really a hypothesis. I'm trying to get you to test that hypothesis before you post it and, if necessary, to modify the hypothesis with the appropriate tentativeness. Don't wait for us to test it for you.

 

Previous posts only mentioned climate as a driver for racial diversity.

 

And I gave you the reasons for that. It isn't as though the idea hasn't been considered.

 

The degree to which sexual attractiveness has influenced human diversity is a mystery to me. It seems logical however, that it has had some influence.

 

There are areas where sexual selection has been seriously considered as a driver in human evolution. There are a couple of studies out showing that human females prefer tall males. Desmond Morris hypothesized that the size and shape of female human breasts were partly due to sexual selection. Some of his data is that larger hemispherical breasts are actually maladaptive for breast feeding. And I mentioned that hairlessness has been proposed to be due to sexual selection. None of these is "diversity", but evolution of H. sapiens as a whole.

 

I think sexual selection for diversity is downplayed simply because the data says that human females of whatever population generally find human males of any other population desirable as mates. Even if they did not, human males find females of any other population desirable as mates and can force the mating if all else fails. Therefore, it's difficult for sexual selection based on population characteristics to be effective. However, since all populations have some taller males than others, that selection can be somewhat effective.

[Glider]

When you are all wrapped up in furs due to the cold, what difference does it make? BTW, are you sure UV is reflected off of ice? You might find that water absorbs light at the UV wavelengths -- most compounds do.

Yes, snow and water can reflect UV. Here's a Wiki entry: "Snow blindness is a painful condition, typically a keratitis, caused by exposure of unprotected eyes to the ultraviolet (UV) rays in bright sunlight reflected from snow or ice. This is especially a problem in polar regions and at high altitudes, as with every thousand feet increase in elevation, the intensity of UV rays goes up five percent.

 

The problem is also related to the condition arc eye sometimes experienced by welders.

 

Snow blindness is akin to a sunburn of the cornea and conjunctiva, and may not be noticed for several hours from exposure. Symptoms can run the gamut from eyes being bloodshot and teary to increased pain, feeling gritty and swelling shut. In very severe cases, snow blindness can cause permanent vision loss."

[lucaspa]

Yes, snow and water can reflect UV. Here's a Wiki entry:

 

I'll accept this because I found it somewhere else -- an .edu site. But please, in an serious discussion, don't use Wiki. Since anyone can write or edit an entry, Wikipedia is a good first source to get an idea of a subject, but can't be used as a source.

 

I will go back to the first question in the part of my post you quoted:

"When you are all wrapped up in furs due to the cold, what difference does it make? "

 

So yes, the eyes get overburdened with UV light, but that doesn't get you enough to make vitamin D. Also, since there are ways to protect against snow blindness (even without sunglasses), reflection of UV off snow and ice during winter still isn't going to get enough vitamin D made for the Inuit.

 

I did a PubMed search. There is a group out of San Diego with 2 recent publications on what constitutes "attractive" mates in 2 human populations:

http://www.ncbi.nlm.nih.gov/sites/entrez?Db=pubmed&Cmd=ShowDetailView&TermToSearch=17160976&ordinalpos=2&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum

http://www.ncbi.nlm.nih.gov/sites/entrez?Db=pubmed&Cmd=ShowDetailView&TermToSearch=17136587&ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVAbstractPlus

 

The first is NW China, the second a community in central Africa. As one test (out of 5) men were asked to ratethe attractiveness of back posed females based skin color. The African males had no preference. The Chinese males did show a preference for lighter-skinned females.

 

The other tests were:

1. Females for average male shape. Both sets of females did not like heavy set men. Chinese females liked average somatotype while the African females liked muscular males.

2. Female preference for amount and distribution of male trunk hair. Chinese women preferred little or no trunk hair, African females did not have a preference except they did not like the hirsute figure.

3. Female preference for the size of the non-erect male penis. Chinese women had a low numerical rating but showed a slight preference for figures with a moderate (22 or 33% above average) lengthening of the penis. African females rejected both the largest and smallest sizes of penis and expressed preference for the intermediate sizes.

4. Male preference for waist to hip ratio (WHR) in females (0.5-1.0). African men liked 0.8, Chinese men liked 0.6 followed by 0.7.

5. Male preference for skin color. See above.

 

Now we wait to see if the group has any further publications with different populations.

[Glider]

I was using Wikipedia to provide a definition of snow blindness, not to support the contention that it exists as a condition. But I take your point, so here are some more reliable links.

 

http://www.emedicine.com/emerg/byname/ultraviolet-keratitis.htm

 

http://www.emedicine.com/EMERG/topic759.htm

 

http://www.basecampmd.com/expguide/snowblind.shtml

[ragemaster]

I was just wondering when the most recent succesful and actually important mutation occured among members of the human race.

[bombus]

Sickle cell syndrome maybe?

 

Also cystic fibrosis.

 

Unfortunately both of these are a disadvantage if you have homologous pairs of the gene (two the same - just having one is an advantage)

[pioneer]

How about the urge to consciously abort the unborn. This was never part of nature, on any large scale. It is even new to humans. It may be due to social environment and medical advances that make this option possible. The jury is still out whether this is progressive or regressive genetics. It gives selective advantage to the older humans, but selective disadvantage to the unborn of the next generation.

 

In nature, the males fight it out and the dominant males gets the gals. Maybe abortion is needed, since the gals are not getting good males. This may be a natural urge to avoid passing on second string genes. This may imply that a secondary genetic change has occurred associated with male regression. Usually the adult males breed, but maybe adolescent males, who are not yet fully adult, mentally, are breeding too often, requiring abortion so the children are not born with regressive genes. I was just trying to use a Darwinian explanation to see where it goes.

[lucaspa]

How about the urge to consciously abort the unborn. This was never part of nature, on any large scale. It is even new to humans.

 

Abortion is "new" to humans, but infanticide is not. Many/most cultures have had a tradition of exposing or outright killing deformed infants. Instead of doing abortion, they just waited until the baby was born.

 

In nature, the males fight it out and the dominant males gets the gals.

 

Not in every species. Even in species that have male domination, the females sneak off to have sex with the beta males. This is well-documented in chimps, for instance.

 

Maybe abortion is needed, since the gals are not getting good males.

 

That's not it. Abortion is a last ditch method of birth control. Every species has a geometric increase in population but an arithmetic increase in resources. Thus, population always outstrips resources. This is the basis of the "struggle for existence" so necessary to natural selection.

 

Humans can, however, consciously control their population, thus keeping it from outstripping resources. This is necessary for technological civilization. If population outstrips resources, you can't maintain civilization. Now, since humans are already at a fitness peak and are well-adapted to their environment, further competition isn't going to result in "improvement", but simply restrict the gene pool. It's called "purifiying selection".

 

I was just wondering when the most recent succesful and actually important mutation occured among members of the human race.

 

Very recently. There are mutations that make individuals immune to HIV, for instance. There are others that increase bone mass (preventing osteoporosis later in life) and some lowering cholesterol and thus preventing cardiac diseases. Mutations for living at high altitude have been documented in 2 populations: Andean and Himalayan highlanders. Different adaptations in both. Since the Andean highlanders have been there less than 10,000 years, those mutations must have come about within that time frame.

 

2. http://www.talkorigins.org/faqs/information/apolipoprotein.html New apo-lipoprotein mutation that adds antioxidant activity.

4. http://content.nejm.org/cgi/content/short/346/20/1513 Mutation giving extra dense bones

6. Pardis C. Sabeti, David E. Reich et. al. Detecting recent positive selection

in the human genome from haplotype structure. Nature 419 24 OCTOBER 2002.

[DrDNA]

http://www.gutenberg.org/catalog/world/readfile?fk_files=38514&pageno=2

[lucaspa]

http://www.gutenberg.org/catalog/world/readfile?fk_files=38514&pageno=2

 

LOL! Nicely done. There's a better source: http://darwin-online.org.uk/

 

I just found out something interesting! Between the 1st and 2nd edition, Darwin added this to the Fontispiece:

"The only distinct meaning of the word 'natural' is stated, fixed, or settled; since what is natural as much requires and presupposes an intelligent agent to render it so, i.e. to effect it continually or at stated times, as what is supernatural or miraculous does to effect it for once."

 

BUTLER: Analogy of Revealed Religion.

[zelta gaisma]

Are there any differences beyond cosmetic? I know some groups are "more prone" to like diabetes but are there any real differences?

[Sisyphus]

Are there any differences beyond cosmetic? I know some groups are "more prone" to like diabetes but are there any real differences?

 

Did you read through this thread?