Has the appearance of Europeans lightened up in 5000 years?

[Moontanman]

New study suggest that just 5000 years ago Europeans had darker skins than they do now. Eye color was also found to be significantly changed over 5000 years..

 

http://www.sciencedaily.com/releases/2014/03/140310182731.htm?

 

Natural selection has altered the appearance of Europeans over the past 5,000 years

Date:

March 10, 2014

Source:

Universität Mainz

Summary:

There has been much research into the factors that have influenced the human genome since the end of the last Ice Age. Anthropologists, geneticists and archaeologists have analyzed ancient DNA from skeletons and found that selection has had a significant effect on the human genome even in the past 5,000 years, resulting in sustained changes to the appearance of people.

 

 

 

[chadn737]

I'm still working through the paper, but I am not fully convinced that they have ruled out the possibility of migration and population discontinuity.

[John Cuthber]

What colour is a "european" today?

I rather suspect that there may now be more black and brown skinned people living in what is currently Europe then there were 5000 years ago in which case the "average" colour is darker than it was.

 

Or are we talking about the group who get called "white" or (even more absurdly) "caucasian" ?

If we are, is this in danger of turning into something that looks like the opposite of a "no true Scotsman" fallacy?

 

(We are only counting white people so they are, by definition , just as white as they always were.)

[chadn737]

What colour is a "european" today?

I rather suspect that there may now be more black and brown skinned people living in what is currently Europe then there were 5000 years ago in which case the "average" colour is darker than it was.

 

Or are we talking about the group who get called "white" or (even more absurdly) "caucasian" ?

If we are, is this in danger of turning into something that looks like the opposite of a "no true Scotsman" fallacy?

 

(We are only counting white people so they are, by definition , just as white as they always were.)

 

I think this is an unnecessary splitting of hairs. European individuals are those whose ancestors have their point of origin in Europe. This definition is actually very robust and when genetic variation of European populations are informed by geological information and plotted by PCA, amazingly reconstruct a map of Europe. This is only possible because there exists within European populations, stratification of the genetic structure of different populations.

 

 

As pigmentation is well studied and understood, we know the genes that are involved. All one needs to do then is look for signatures of selection by comparing changes that have occurred in ancestral populations and modern populations.

 

Furthermore, since they have genetic data, they were able to test for the possibility of population continuity from the mitochondrial data. When they did this, they showed that the modern populations tested were most likely descendants of the ancestral populations they tested. Individuals whose ancestors had other points of origin would not demonstrate this continuity based on mitochondrial data.

 

And no, white people are not as white as they always were. The entire point of this paper is showing that the likely ancestors of white Europeans were not white 5000 years ago and the change in pigmentation is something that happened recently and rapidly due to natural selection. This is interesting because the change in pigmentation within European populations occurred very rapidly, which indicates that natural selection was acting very strongly on this trait. Its informative about human evolution in this region of the world.

 

My one caveat to this is that the assumption of population continuity is based on mitochondrial data, whereas the nuclear genome would be even more informative, given the possibility of migration and admixture.

Edited March 11, 2014 by chadn737

[John Cuthber]

"I think this is an unnecessary splitting of hairs. European individuals are those whose ancestors have their point of origin in Europe. This definition is actually very robust"

Are you sure about that?

I'm fairly sure that all of us have ancestors based in Africa.

 

http://en.wikipedia.org/wiki/Recent_African_origin_of_modern_humans

 

It's an interesting topic, but it needs some very clear definitions to get anywhere.

[chadn737]

"I think this is an unnecessary splitting of hairs. European individuals are those whose ancestors have their point of origin in Europe. This definition is actually very robust"

Are you sure about that?

I'm fairly sure that all of us have ancestors based in Africa.

 

http://en.wikipedia.org/wiki/Recent_African_origin_of_modern_humans

 

It's an interesting topic, but it needs some very clear definitions to get anywhere.

 

Sure, if you go back far enough, but there is a reason why there is genetic structure associated with geography. Since man has left Africa, he has continued to evolve and with that develop regional differences both at the phenotypic and genetic levels. I don't see what is ambiguous about the the term "European". Certainly within the context of the study presented, the definitions are robust enough to show evidence of population continuity and selection. If such population structure did not exist, then there would be no signatures of selection, no evidence for population continuity, etc.

[overtone]

If the( by now almost standard) hypothesis that the selection for skin transparency to UV radiation was by Vitamin D shortages in northern latitudes inland from ocean sources, one would expect a sudden increase of that pressure on the people who followed the vegetation, large mammals, and ice retreat into the north and back toward the mountains from the coast, at the end of the last glaciation.

 

The darker complexioned ones would have been disadvantaged.

[Moontanman]

If the( by now almost standard) hypothesis that the selection for skin transparency to UV radiation was by Vitamin D shortages in northern latitudes inland from ocean sources, one would expect a sudden increase of that pressure on the people who followed the vegetation, large mammals, and ice retreat into the north and back toward the mountains from the coast, at the end of the last glaciation.

 

The darker complexioned ones would have been disadvantaged.

 

 

Not necessarily, primates cannot make Vitamin C but most other animals can, I'm not sure but other animals might make their own Vitamin D....

 

Also, humans cover their bodies with clothes which could interfere with absorbing sunlight as well...

Edited March 11, 2014 by Moontanman

[Iota]

It's an interesting topic, but it needs some very clear definitions to get anywhere.

 

Come on man... lighten up.

[StringJunky]

Could covering up their bodies due to cooler cloudier climates have facilitated the selection of lighter skin in such a short time?

[Ophiolite]

Could covering up their bodies due to cooler cloudier climates have facilitated the selection of lighter skin in such a short time?

250 generations. Is that a short time?

[StringJunky]

250 generations. Is that a short time?

Isn't it? In evolutionary terms?

[Ophiolite]

Isn't it? In evolutionary terms?

The Galapagos finches seem to be able to produce marked changes within a handful of generations when responding to environmental changes and drawing on natural variations within the population. Intuitively I don't see it as being a problem. But I'm not well versed in general evolutionary rates, which is why I was asking if that was short. My gut tells me no, but what does my gut know?

[StringJunky]

The Galapagos finches seem to be able to produce marked changes within a handful of generations when responding to environmental changes and drawing on natural variations within the population. Intuitively I don't see it as being a problem. But I'm not well versed in general evolutionary rates, which is why I was asking if that was short. My gut tells me no, but what does my gut know?

You may well be right but my question was from a learning perspective not argumentative. Would being dark-skinned in a UV-poor environment be a significant enough disadvantage to cause a change in a population with that property in five millennia?.

Edited March 12, 2014 by StringJunky

[chadn737]

The calculated selection coefficients (essentially how strong natural selection is operating) for the three genes in question are on par with the selection coefficients for lactase tolerance, genes involved in high-altitude living, and the sickle cell genes in malaria areas (although this latter is actually a case of balancing selection so its more complicated). These are all cases of very strong and recent selection, so it is very interesting.

 

The real debate is whether or not there is actual population continuity in the area. Migration could mimic at some level the effects of selection. Though this group showed strong evidence of population continuity through the mitochondria, there is a possibility that its paints a false picture. There are known instances where based on Y-chromosome inheritance, one would assume population continuity, but looking at the entire nuclear genome this assumption breaks down.

[overtone]

250 generations. Is that a short time?

Isn't it? In evolutionary terms?

Not for such plastic traits (in humans) as skin and eye color. They are among the most easily and quickly altered traits humans possess - so much riding on this plasticity that evolution has established a meta-level, an evolved ability to alter skin tone in response to environment (tanning). There are northern India groups of European origin and lactose tolerance (related to Latvians, iirc) that have become racially US black apparently within recorded history (if early Greek and Roman writings are entered as history).

 

Athough it's complicated: http://www.cam.ac.uk/research/news/light-skin-gene-mirrors-socio-cultural-boundaries-in-indian-population

 

Considering that vitamin D deficiency directly affects reproduction at the level of female fecundity, gestation and successful childbirth and early chodhood nutrition, while skin cancer and sunburn's effects kill even the prereproductive young, the evolutionary pressure during the colonization of northern Europe after the most recent glacial era might easily have been dramatic.

Edited March 13, 2014 by overtone

[chadn737]

Not for such plastic traits (in humans) as skin and eye color. They are among the most easily and quickly altered traits humans possess - so much riding on this plasticity that evolution has established a meta-level, an evolved ability to alter skin tone in response to environment (tanning). There are northern India groups of European origin and lactose tolerance (related to Latvians, iirc) that have become racially US black apparently within recorded history (if early Greek and Roman writings are entered as history).

 

Athough it's complicated: http://www.cam.ac.uk/research/news/light-skin-gene-mirrors-socio-cultural-boundaries-in-indian-population

 

Considering that vitamin D deficiency directly affects reproduction at the level of female fecundity, gestation and successful childbirth and early chodhood nutrition, while skin cancer and sunburn's effects kill even the prereproductive young, the evolutionary pressure during the colonization of northern Europe after the most recent glacial era might easily have been dramatic.

 

I disagree with your first assertion regarding plastic traits. There is no reason to believe that plastic traits normally have higher selection coefficients and this is still remarkably fast evolution and strong selection regardless of the plasticity.

 

The case of the Indian groups is actually one of migration and admixture. This is why in India you find an abundance of Y chromosomes from Europe, but in the rest of the genome, there is clear evidence of admixture. As I stated earlier, if not properly taken into account, migration and admixture can appear as very strong natural selection when in fact it is a matter of migration. The study here claims that there is population continuity and thus what is observed is selection and not migration. The two situations are rather distinct.

Edited March 13, 2014 by chadn737

[Arete]

Not for such plastic traits (in humans) as skin and eye color.

 

The number of generations in isolation is not sufficient to determine evolutionary potential. You would also need to know effective population size (Ne) and the population mutation rate (θ) to determine any evolutionary rate in a given population.

[overtone]

 

 

I disagree with your first assertion regarding plastic traits. There is no reason to believe that plastic traits normally have higher selection coefficients and this is still remarkably fast evolution and strong selection regardless of the plasticity.

? My assertion?

 

My observations were that we have very good reasons to expect strong selection pressure on factors affecting vitamin D metabolism among the released populations and colonizers of a post-glacial era inland northern Europe or west central Asia, and that skin color in humans (one of those factors, a major one) is plastic - controlled by a relatively small set of quite variable and easily selected genetic code stretches whose functions are only lightly embedded elsewhere in the physiology. So the stage was set for very rapid evolutionary change in skin color, back in the day. So although interesting, such rapid evolution would not be shocking, if it checks out.

 

 

 

The case of the Indian groups is actually one of migration and admixture. This is why in India you find an abundance of Y chromosomes from Europe, but in the rest of the genome, there is clear evidence of admixture. As I stated earlier, if not properly taken into account, migration and admixture can appear as very strong natural selection when in fact it is a matter of migration

Admixture and selection are not remotely exclusive - selection from mixture is a standard evolutionary sequence.

[chadn737]

? My assertion?

 

My observations were that we have very good reasons to expect strong selection pressure on factors affecting vitamin D metabolism among the released populations and colonizers of a post-glacial era inland northern Europe or west central Asia, and that skin color in humans (one of those factors, a major one) is plastic - controlled by a relatively small set of quite variable and easily selected genetic code stretches whose functions are only lightly embedded elsewhere in the physiology. So the stage was set for very rapid evolutionary change in skin color, back in the day. So although interesting, such rapid evolution would not be shocking, if it checks out.

 

 

1) This statement and your previous one regarding plasticity and genetics seems to conflate phenotypic plasticity with the idea that the underlying genetics is therefore hypervariable and somehow more prone to mutation/selection/frequency changes. Is that what you are actually saying? Because you can't simply assume that. There may be a large number of alleles in skin pigmentation genes, but just because the trait itself has some plasticity does not necessarily mean that the genes themselves are more variable than any other traits or that they should be under stronger selection. In fact, if there is a large amount of genetic diversity underlying a trait, that is oftentimes a sign of weak selection. Vitamin D is important, I don't deny that, but I'm taking issue with the emphasis you place on plasticity. There is reason to argue that highly plastic traits reduce the effects of selection because the phenotypes can change/adapt within a set range without the underlying genetics necessarily changing. If your body can produce more Vitamin D by simply not producing as much melatonin without genetic changes, then selection is not going to be as strong. So I am very confused by the unusual emphasis you place on plasticity. Perhaps you mean something different than the standard usage. Maybe you mean that because it is more variable between individuals that this is "plasiticity"?

 

 

2) Human skin pigmentation is not so simple of a trait. While a relatively handful of genes explain a large portion of the variance between such disparate populations as say Northern Europeans and Africans, there is likely a great deal more genes involved in the differences within populations. There are after all at least 77 genes in humans with evidence of playing a role in skin pigmentation and in one study at least 18 showed signs of positive selection. Many of the loci identified have been limited by the fact that the trait has been most extensively studied by taking candidate gene approaches and comparing disparate ancestral populations. In contrast, when admixed populations were studied, many new genes are identified. In comparison to other human quantitative trait, certainly skin pigmentation is more simple and straight forward, but that is only at a relative scale.

 

3) On what basis do you claim that the genetics skin pigmentation is not "lightly embedded elsewhere in the physiology". First of all, I'm not really sure what is meant by "lightly embedded"....this is a word choice that makes little sense to me. Do you mean that these genes are not involved in other physiological processes? Do you mean that there is little relation between the physiology of skin pigmentation and other processes? I have no idea... Many genes involved with skin pigmentation can have very profound effects on vision. KITLG is a crucial part of haematopoiesis.

 

4) Rapid evolution and strong selection is surprising. Just because it makes sense why a gene would be under selection, it does not follow that the selection should be so strong. There are lots of advantageous or disadvantageous traits that are under relatively weak selection, even though it makes sense why it would be. I think we should appreciate the fact that if there was population continuity, that the selection was very strong.

 

Admixture and selection are not remotely exclusive - selection from mixture is a standard evolutionary sequence.

 

You completely missed the point and this is a strawman.

 

1) I never said admixture and selection are mutually exclusive.

 

2) The point of bringing up migration and admixture is because migration changes allele frequencies independently of selection. If we recall the rules of Hardy-Weinberg Equilibrium, in order to have equilibrium, there has to be no selection and no migration. In the absence of selection and with migration, allele frequencies will change. The way the selection coefficients are calculated, especially in the case of this study, was based on changes in allele frequency from ancient samples and modern samples. The authors assumed no migration in this instance based on mitochondrial DNA samples. However, if there was migration, then this could drastically alter the changes in allele frequencies alone. In this case, the strength of selection would actually be lower than those calculated in this study. I bring up the example of Y-chromosome lineages in India as an example, because the Y-chromosome, like the mitochondria, is inherited from one parent. In the case of Y-chromosome lineages and India, if one were to base population continuity off the Y-chromosome, you would likely conclude incorrectly that there was population continuity. The same difficulty lies with doing so with the mitochondrial genomes.

 

So do you see my point? Nobody claimed that admixture and selection are mutually exclusive....what is at issue here is whether or not migration occurred and what effect that had on the strength of selection.

[overtone]

 

 

1) This statement and your previous one regarding plasticity and genetics seems to conflate phenotypic plasticity with the idea that the underlying genetics is therefore hypervariable and somehow more prone to mutation/selection/frequency changes. Is that what you are actually saying?

Tell you what, why don't you just go back and read what I wrote without adding words like "phenotypic", under the assumption that if I intended to mean "phenotypic plasticity" I would have written "phenotypic plasticity" instead of what I wrote.

 

That general principle - reading the words posted without adding one's own adjectives and "seemings" and so forth - will serve you well in reading my posts generally, and save us a load of repetition and so forth.

 

 

 

As I stated earlier, if not properly taken into account, migration and admixture can appear as very strong natural selection when in fact it is a matter of migration

- - - -

So do you see my point? Nobody claimed that admixture and selection are mutually exclusive....what is at issue here is whether or not migration occurred and what effect that had on the strength of selection.

So you have no objection to my posting, which simply illustrated by example the fact that evolutionary change in skin color, is something that can happen very rapidly in people for well known reasons - 5000 years is not a shock.

 

That the evolutionary case there is one of migration, admixture, and selection.

[chadn737]

Tell you what, why don't you just go back and read what I wrote without adding words like "phenotypic", under the assumption that if I intended to mean "phenotypic plasticity" I would have written "phenotypic plasticity" instead of what I wrote.

 

That general principle - reading the words posted without adding one's own adjectives and "seemings" and so forth - will serve you well in reading my posts generally, and save us a load of repetition and so forth.

 

In the biological context, plasticity always refers to phenotypic plasticity, unless you are talking about neuroplasticity, which is also phenotypic. How else am I going to interpret that?

 

As for what you wrote, lets look at the context:

 

"Not for such plastic traits (in humans) as skin and eye color."

 

Hmm, there you are talking about "traits" which in biology refers to phenotype: A qualitative characteristic; a discrete attribute as contrasted with metrical character. A trait is amenable to segregation rather than quantitative analysis; it is an attribute of phenotype, not of genotype.

 

Not only that, but you refer to it specifically in the context of skin and eye color....those are phenotypes!

 

How about this one:

 

"They are among the most easily and quickly altered traits humans possess - so much riding on this plasticity that evolution has established a meta-level, an evolved ability to alter skin tone in response to environment (tanning)."

 

You are still talking about traits (phenotypes, skin tone (a phenotype), and now tanning (another phenotype).

 

"My observations were that we have very good reasons to expect strong selection pressure on factors affecting vitamin D metabolism among the released populations and colonizers of a post-glacial era inland northern Europe or west central Asia, and that skin color in humans (one of those factors, a major one) is plastic"

 

Vitamin D metabolism and skin tone.....both phenotypes.

 

Every time you have talked about plasticity you have talked about phenotypes or used the term "trait" which specifically refers to phenotype. Then there is the basic fact that biological plasticity refers to phenotype.

 

So if you meant it to mean something else, you certainly did not imply as much and you certainly used incorrect terminology. Now when challenged on it you want to imply to me that you meant something else other than phenotypic plasticity? Come on man, you're changing your stories and if you're not, then you need to familiarize yourself with correct terminology.

 

So you have no objection to my posting, which simply illustrated by example the fact that evolutionary change in skin color, is something that can happen very rapidly in people for well known reasons - 5000 years is not a shock.

 

Very strong and rapid positive selection is not all that common. There is a reason so many human geneticists have been surprised by the strength of the selection. If you don't find it surprising, then so what.

 

That the evolutionary case there is one of migration, admixture, and selection.

 

Has there been selection? You claimed it was a matter of selection, but never supported this claim. That there was migration and admixture is well documented, hence my point about the Y-chromosomes. But again, my entire point regarding India is that the history is the exact opposite. There you have population discontinuity, in this case, you have a claim of population continuity, the result being very different effects on allele frequency changes and how strong selection actually was.

[overtone]

 

 

In the biological context, plasticity always refers to phenotypic plasticity, unless you are talking about neuroplasticity, which is also phenotypic. How else am I going to interpret that?

Uh, no - fifty second google: http://scholar.google.com.au/scholar?q=evolution+%22genetic+plasticity%22&hl=en&as_sdt=0&as_vis=1&oi=scholart&sa=X&ei=cD0jU8vEJ-SkyAHNloGgBA&ved=0CCcQgQMwAA

 

You might have simply read the word for its English meaning, granting respect to the argument in front of you, of course: Plasticity is not a technical term, and I'm not a technical person, and this is not a jargon-bound technical venue.

 

As the rest of your reply simply expands on that initial failure to follow the argument, and the argument is pretty simple, might I again simply recommend a rereading? It wasn't that profound an observation, there in post 16 with the link and all.

 

 

 

Very strong and rapid positive selection is not all that common.

In general, no. For skin color in humans, however, we have considerable evidence that it has happened several times and possibly under several different selection regimes, within less than 2500 generations certainly and possibly a fifth of that. There are something like half a dozen distinct and genetically governed skin color groups in our species, and at least one example of at least a three stage "reversal" - black/black to white to brown/black - within the time of the sapiens takeover of inland Europe and central Asia.

[chadn737]

Uh, no - fifty second google: http://scholar.google.com.au/scholar?q=evolution+%22genetic+plasticity%22&hl=en&as_sdt=0&as_vis=1&oi=scholart&sa=X&ei=cD0jU8vEJ-SkyAHNloGgBA&ved=0CCcQgQMwAA

 

You might have simply read the word for its English meaning, granting respect to the argument in front of you, of course: Plasticity is not a technical term, and I'm not a technical person, and this is not a jargon-bound technical venue.

 

As the rest of your reply simply expands on that initial failure to follow the argument, and the argument is pretty simple, might I again simply recommend a rereading? It wasn't that profound an observation, there in post 16 with the link and all.

 

 

The common usage of this word is in reference to traits. Consider the fact that a search for "phenotypic plasticity" yields over 20x more results than "genetic plasticity". That you can find published alternative usages of plasticity is not a surprise, I admit that using the word "always" was way to strong and wrong, but just because you can find examples, does not mean that this is the common or proper usage. Quite frankly, "genetic plasticity" implies a view of the genome that is very problematic and I take issue with it, but that is beyond the scope of this discussion.

 

However, in your posts, you always used the word "plastic" in conjunction with "traits" or specific phenotypes, thus implying "phenotypic plasticity". So even if there are minor alternative usages of this word, the context of your previous posts clearly implies "phenotypic plasticity" not genetic.

 

Let me quote you directly once again:

 

"Not for such plastic traits (in humans) as skin and eye color."

 

While there is arguably some ambiguity in the term "plasticity" there is no ambiguity in the term "trait" or in the specific phenotypes you listed off in reference to their "plasiticity".

 

Perhaps you should reread what you actually wrote. If you meant something other than phenotypic plasticity, then you probably shouldn't use a phrase like "plastic traits". How do you claim to not have been talking about phenotypic plasticity when every time you use the words "plastic" or "plasticity" it is to modify words like "trait" or specific phenotypes.

 

In general, no. For skin color in humans, however, we have considerable evidence that it has happened several times and possibly under several different selection regimes, within less than 2500 generations certainly and possibly a fifth of that. There are something like half a dozen distinct and genetically governed skin color groups in our species, and at least one example of at least a three stage "reversal" - black/black to white to brown/black - within the time of the sapiens takeover of inland Europe and central Asia.

 

 

That skin color has evolved multiple times is not surprising. What is surprising is the strength of selection in this instance. Can you cite any other studies that show selection coefficients for skin color as strong as these? Again, the point is not that skin color has not evolved multiple times, its how strongly it was selected for in this instance. Its not enough to simply state "within less than X generations" because the strength of selection is not a simple function of the number of generations. As Arete pointed out earlier, crucial to knowing the strength of selection is the effective populations size (N_e). The assumption of population continuity or discontinuity also is crucial, as I have pointed out several times.

 

So, just because it has evolved multiple times, does not mean that the selection on the trait has been as strong in the other instances. So unless you can show that the selection has been as high in all these other circumstances, its still surprising.

Edited March 14, 2014 by chadn737

[overtone]

 

 

That skin color has evolved multiple times is not surprising. What is surprising is the strength of selection in this instance. Can you cite any other studies that show selection coefficients for skin color as strong as these?

I have cited no studies showing selection coefficients at all, as far as I noticed.

 

I simply observed that skin colors in human populations have evolved rapidly quite often in the past, the genetics are plastic (set up to allow sensitivity to selection pressure, unlike, say, design height or digestive tract physiology), and a couple of selection pressures on the humans populating inland and northern Europe during the post-glacial warming are both obvious and in apparent likelihood very strong. I find that situation unexceptional, actually, among the population expansions of mammals and birds and probably vertebrates generally, but whether it is unique to humans or not it is observation from which the ordinary conclusions (right or wrong) might be drawn without much shock - why not?

 

 

However, in your posts, you always used the word "plastic" in conjunction with "traits" or specific phenotypes, thus implying "phenotypic plasticity". So even if there are minor alternative usages of this word, the context of your previous posts clearly implies "phenotypic plasticity" not genetic.

And yet another 50 second google, this time to an ordinary Wiki page: http://en.wikipedia.org/wiki/Genetics

 

 

Genetics is the process of trait inheritance from parents to offspring, including the molecular structure and function of genes, gene behavior in the context of a cell or organism (e.g. dominance and epigenetics), gene distribution, and variation and change in populations. Given that genes are universal to living organisms, genetics can be applied to the study of all living systems, including bacteria, plants, animals, and humans. The observation that living things inherit traits from their parents has been used since prehistoric times to improve crop plants and animals through selective breeding.^{[6] - - -}

 

Again, the recommendation would be to give up on that entire approach to my posts. You don't know what you're doing. Just read the words for their meanings in the English language, derive from that reading the meaning of the post, and respond accordingly.