A climatic OTL history question and evolutionary question

  1. Might the Little Ice Age have had anything to do with the success of European colonization of the subtropical and tropical regions of the Americas? Of course, disease was the most important thing, followed by a technology advantage, then geopolitics affecting the Aztecs and Incas, but might the slightly cooler temperatures in places south of New Jersey and north of Rio de la Plata have helped the Europeans in any way? Kind of like how the Medieval Warm Period allowed the Vikings to settle Greenland?
  2. Evolution of human skin tone. Is it only based on latitude, or also on temperature? If the whole world became a lot warmer, and you waited 300,000 years, would everyone be darker? Does altitude have an effect? What about albedo of the surrounding environment that a group of people lives?
 

BlondieBC

Banned
  1. Evolution of human skin tone. Is it only based on latitude, or also on temperature? If the whole world became a lot warmer, and you waited 300,000 years, would everyone be darker? Does altitude have an effect? What about albedo of the surrounding environment that a group of people lives?

Neither, Skin tone relates to how much sunshine your ancestors received each day. A person in a very foggy location nearer to the equator may have a darker skin than a person in a desert that is located farther from the equator.

If you live in a low light location and your skin is too dark, you suffer from Ricketts, and your genes are less likely to pass on. If you are too light in a high sunshine area, you will have much higher skin cancer rates, and your genes are less likely to be passed on.

It takes about 10,000 years for a population genes to flip from light to dark.
 
Neither, Skin tone relates to how much sunshine your ancestors received each day. A person in a very foggy location nearer to the equator may have a darker skin than a person in a desert that is located farther from the equator.

If you live in a low light location and your skin is too dark, you suffer from Ricketts, and your genes are less likely to pass on. If you are too light in a high sunshine area, you will have much higher skin cancer rates, and your genes are less likely to be passed on.

It takes about 10,000 years for a population genes to flip from light to dark.
Wouldn't it be that the person in very foggy location would be lighter, since the fog would block much of the light? Of course it depends on the distance from the equator for each person.

So temperature doesn't matter, just light level, am I correct? (ignoring vitamin D in the diet)

I said 300,000 to be absolutely sure that the change would occur in time, though that would probably result in the evolution of a whole new subspecies. Also, it takes less than 10,000 years if there are already many different skin tone genes in the population, while it can take many more if they aren't. For example, there are no black native Americans. And they crossed 17,000 years ago. Even if it took a full 7,000 years to arrive at the equator, they'd still have the alleged 10,000 years. Even the natives that had almost the full 17,000 years, those in Canada, are, according to their latitude, not yet adapted.
 

BlondieBC

Banned
Wouldn't it be that the person in very foggy location would be lighter, since the fog would block much of the light? Of course it depends on the distance from the equator for each person.

So temperature doesn't matter, just light level, am I correct? (ignoring vitamin D in the diet)

I said 300,000 to be absolutely sure that the change would occur in time, though that would probably result in the evolution of a whole new subspecies. Also, it takes less than 10,000 years if there are already many different skin tone genes in the population, while it can take many more if they aren't. For example, there are no black native Americans. And they crossed 17,000 years ago. Even if it took a full 7,000 years to arrive at the equator, they'd still have the alleged 10,000 years. Even the natives that had almost the full 17,000 years, those in Canada, are, according to their latitude, not yet adapted.

You are right, I flipped the sentence, it was late at night. Less sunlight for ancestors indicated lighter skin. It is from an article I read years ago, but there are multiple population groups that have made the flip in 10,000 years. There is enough light and dark genes in every group to be selected for over 10K years. After all, Humans are all Africans, 70,000 years ago.
 
Wouldn't it be that the person in very foggy location would be lighter, since the fog would block much of the light? Of course it depends on the distance from the equator for each person.

So temperature doesn't matter, just light level, am I correct? (ignoring vitamin D in the diet)

I said 300,000 to be absolutely sure that the change would occur in time, though that would probably result in the evolution of a whole new subspecies. Also, it takes less than 10,000 years if there are already many different skin tone genes in the population, while it can take many more if they aren't. For example, there are no black native Americans. And they crossed 17,000 years ago. Even if it took a full 7,000 years to arrive at the equator, they'd still have the alleged 10,000 years. Even the natives that had almost the full 17,000 years, those in Canada, are, according to their latitude, not yet adapted.
But the Native Americans can be brown skinned, even if their ancestors became light skinned.
 
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You are right, I flipped the sentence, it was late at night. Less sunlight for ancestors indicated lighter skin. It is from an article I read years ago, but there are multiple population groups that have made the flip in 10,000 years. There is enough light and dark genes in every group to be selected for over 10K years. After all, Humans are all Africans, 70,000 years ago.
Not in Native Americans, who have only 70 common ancestors from Siberia, all of whom were probably medium brown. Even though they may be the most culturally diverse group, they are the least genetically diverse.

But the Native Americans can be brown skinned, even if their ancestors became light skinned.
They are all brown-skinned. Even though the Amazonians 'should' be black and Iroquois 'should' be white according to light level.
 
Not in Native Americans, who have only 70 common ancestors from Siberia, all of whom were probably medium brown. Even though they may be the most culturally diverse group, they are the least genetically diverse.

They are all brown-skinned. Even though the Amazonians 'should' be black and Iroquois 'should' be white according to light level.

There is variation within the Amerindian population, however they are quite a recent population movement, probably 11 thousand years old at most. Plus that lack of genetic diversity slows the rate of adaption due to a limited allele pool to work on.

Secondly they have similar skin tones to many groups at comparable latitudes, the ultra-pasty white europeans are due to the overcast nature of northern europe, nearly all of the americas receive more average insolation:

world_solar_radiation_large.gif


Secondly whilst pastiness is an adaption to very low light, dark skin is not as strongly selected for in high light (indeed there is evidence the high melanin content in African populations is due to a secondary effect to resist a number of diseases), so the Siberian hunters the Amerindians were ten millenia ago haven't had nearly the time needed to darken (not to mention the Americas aren't as high sunlight).
 
There is variation within the Amerindian population, however they are quite a recent population movement, probably 11 thousand years old at most. Plus that lack of genetic diversity slows the rate of adaption due to a limited allele pool to work on.

Secondly they have similar skin tones to many groups at comparable latitudes, the ultra-pasty white europeans are due to the overcast nature of northern europe, nearly all of the americas receive more average insolation:

Secondly whilst pastiness is an adaption to very low light, dark skin is not as strongly selected for in high light (indeed there is evidence the high melanin content in African populations is due to a secondary effect to resist a number of diseases), so the Siberian hunters the Amerindians were ten millenia ago haven't had nearly the time needed to darken (not to mention the Americas aren't as high sunlight).
Is albedo the reason that the equator doesn't have the highest light level? (the dark green rainforest trees absorbing the light)

Also, that map explains a lot. Why Southern Chinese aren't all that much darker than Northern Chinese, why some native Peruvians are pretty dark even though Amazonians are light, why Nubians were black despite being as far north as north Sudan is, etc.

Thanks that was a helpful answer.
 
In response to the evolution question; it is based on the amount of light as others have said above, although I have heard the case that it also depends on sexual selection (for example, the Aztecs definitely did not compare with their Saharan counterparts) but remember the period for selection when natural selection is the only selective agent varies based on time and location.
 
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