What was the complexion of the early humans?

[sethoflagos]

Radiative cooling is small at these sort of temperatures- especially when surrounded by stuff at similar temperatures.

The rate of heat loss will depend (slightly) on how well the skin absorbs far infra red.

That's not going to be closely correlated with colour which depends on how well it absorbs visible light.

 

It's of the order 10W per degree difference between skin temperature and environment. The shade temperature typically for the African equatorial belt is rarely above 32 C. Usually a bit less. A resting human can typically get their metabolic thermal output down to around 70W.

 

These ballpark figures indicate that radiative cooling could conceivably be a significant survival factor in a crisis. The skin pigment to emissivity relationship at the relevant frequencies (around 10 microns), I've no idea.

 

I don't claim that it's the full picture, but I do see a certain amount of evidence around me and would be interested to see some proper research done on this. On an African population in particular. Rather than have it inferred from studies of other populations, which is what we see so often.

Edited August 10, 2016 by sethoflagos

[DrmDoc]

 

It's of the order 10W per degree difference between skin temperature and environment. The shade temperature typically for the African equatorial belt is rarely above 32 C. Usually a bit less. A resting human can typically get their metabolic thermal output down to around 70W.

 

These ballpark figures indicate that radiative cooling could conceivably be a significant survival factor in a crisis. The skin pigment to emissivity relationship at the relevant frequencies (around 10 microns), I've no idea.

 

I don't claim that it's the full picture, but I do see a certain amount of evidence around me and would be interested to see some proper research done on this. On an African population in particular. Rather than have it inferred from studies of other populations, which is what we see so often.

If I may and not to again beleaguer the point, early modern humans were exclusively an African population even as they migrated to lower UV (European) climates and evolved lighter skin colors. The research evidence I referenced through the article link I provided is based on DNA samplings linked to those migrating early modern humans.

Edited August 10, 2016 by DrmDoc

[Strange]

Presumably southern Africa is lower UV than, say, equatorial Africa. So perhaps it isn't surprising that would see some variation - especially among groups such as the San. But without the single point change that appears to be common to northern / white populations.

[DrmDoc]

Presumably southern Africa is lower UV than, say, equatorial Africa. So perhaps it isn't surprising that would see some variation - especially among groups such as the San. But without the single point change that appears to be common to northern / white populations.

 

I agree; however, the early fossil remains of modern humans found at the Omo 1 site in Ethiopia continues to suggest exposure to high UV levels and the probability of darker skin among early humans than populations now found in southern Africa.

Edited August 10, 2016 by DrmDoc

[John Cuthber]

 

It's of the order 10W per degree difference between skin temperature and environment. The shade temperature typically for the African equatorial belt is rarely above 32 C. Usually a bit less. A resting human can typically get their metabolic thermal output down to around 70W.

 

These ballpark figures indicate that radiative cooling could conceivably be a significant survival factor in a crisis. The skin pigment to emissivity relationship at the relevant frequencies (around 10 microns), I've no idea.

 

I don't claim that it's the full picture, but I do see a certain amount of evidence around me and would be interested to see some proper research done on this. On an African population in particular. Rather than have it inferred from studies of other populations, which is what we see so often.

People are mainly water. Water is a very strong absorber near 10 microns (about the wavelength we would be emitting).

On that basis I strongly suspect that melanin can't make much difference.

 

Also, it's not when you are dissipating 70 Watts that you are at risk of overheating.

It's when you are running at 700 Watts.

 

I suspect that the widely held belief that melanin is used as a UV screen is more viable

[sethoflagos]

People are mainly water. Water is a very strong absorber near 10 microns (about the wavelength we would be emitting).

On that basis I strongly suspect that melanin can't make much difference.

 

Also, it's not when you are dissipating 70 Watts that you are at risk of overheating.

It's when you are running at 700 Watts.

 

I suspect that the widely held belief that melanin is used as a UV screen is more viable

 

Why do you guys have so much difficulty in embracing the concept of multiple evolutionary drivers?

 

There's no doubt that probably around the time we lost most of our body hair, MC1R became very strongly conserved under strong selective pressure to darken our pale ancestral (chimp-like) skin.

 

There can be little doubt that the strong UVR protection provided by eumelanin producing melanocytes played a part in that. Possibly a dominant part. And it still remains highly conserved, almost invariant in most African populations.

 

But there are a number of points to address here:

 

1) Active MC1R does not necessarily turn the individual jet black. It covers very nearly the whole gamut from a golden fawn upwards (and that's leaving aside albinism). This is at least partly under environmental control.

 

2) Susceptibility to mortality in adulthood from skin cancer has never seemed sufficiently strong a driver to explain the conservation of MC1R. The strength of that conservation has more than a hint that eg sexual selection played a role too.

 

3) You seem happy to accept the idea that MC1R ceases to be conserved (quite quickly apparently) in a slightly lower UV intense region as southern Asia, yet reluctant to acknowledge the many African populations, particularly those of Central and Western Africa where rain forest shielded them from UV far more effectively than a few degrees of northern latitude and for a considerably longer period of time without MC1R degradation.

 

4) And why doesn't MC1R reestablish its monopoly in high UV areas elsewhere in the world?

 

5) You can suspect the contrary as much as you like, but your utter dismissal of thermoregulation as a significant evolutionary player in the development of our species speaks volumes. Google 'cursorial hunting' then tell me that heat stress hasn't been a factor in who lived and who died.

Edited August 10, 2016 by sethoflagos

[CharonY]

With regard to OP, it is assumed that darker pigmentation accompanied fur loss during human evolution in equatorial Africa. However skin damage/cancer is, for a number of reasons not very likely. A compelling hypothesis put forward by Jablonski and Chaplin is that instead cost in terms of folate, (high breakdown and is also required to address UV-damages such as forDNA repair) has been the driving factor. Dispersal out of Africa then created a different situation with the need of increased vitamin D photosynthesis.

 

While I am not entirely sure how it addresses OP, skin color range is clearly determined by a moderately large set of genes and not a single gene or allelic variation. SLC24A5 accounts for up to 40% of pigmentation (I think it is either Kivisild's work or he cites someone's on this)differences and is probably a main element of vitamin D adaptation but obviously other alleles contribute to the variations that we find inside and outside of Africa.

Regardless, it is almost certain that our ancestors were very dark-skinned.

[sethoflagos]

Regardless, it is almost certain that our ancestors were very dark-skinned.

 

I was fine with you up to this final point. But if moderate 'darkness' yielded sufficient advantage to balance African level UVB flux over the somewhat lower fluxes of elsewhere, then where is the driver for 'very dark'?

 

'Very dark' is at least in modern times a minority characteristic in Africa both locally and as a whole.

[CharonY]

I think in that case it would be beneficial to start using a scale of human complexion and discuss what you mean with moderate darkness. In my case I used it to differentiate it from lighter complexions the further we move away from the equator.

[sethoflagos]

How about the example given for haplogroups L3, E, B from the National Geographic site on the human genome project.

 

 

An Algerian subject which one would expect to be subject to very high incident levels of UVB.

[John Cuthber]

 

Why do you guys have so much difficulty in embracing the concept of multiple evolutionary drivers?

 

 

I was talking about spectroscopy- not evolution.

The fact is that black + white skins lose heat by radiation at pretty much the same rate because, in the far IR where people radiate, water is black,

So, why the stuff about my lack of understanding- when you were the one who missed the point?

[sethoflagos]

I was talking about spectroscopy- not evolution.

The fact is that black + white skins lose heat by radiation at pretty much the same rate because, in the far IR where people radiate, water is black,

So, why the stuff about my lack of understanding- when you were the one who missed the point?

 

The point wasn't missed, it was ignored as (IMHO) non sequitur.

 

Maybe a more constructive way of blowing my hypothesis out of the water would have been to refer me to something like 'Spectral Emissivity of Skin and Pericardium' (Steketee). From which I learn that the emissivities of pale and dark human skin in the mid-IR are not only equal, they are both phenomenally high. Much higher than water, higher even than black rubber and charcoal.

 

Now that is food for thought!

Edited August 11, 2016 by sethoflagos

[CharonY]

Looking at UV maps in Algeria the UV radiation ranges from high to moderate whereas countries closer to the equator seem to exceed it on most days in the respective summer months (though a full data set would be helpful to properly asses this).

Specifically regarding the haplogroups: off the top of my head L3 E is present throughout Africa, and includes populations with much darker skin than the one you pictured (or to put it differently L3E is not associated with the that particular skin hue), It is most closely associated with Bantu migrations, which as you may know, are often having darker skin. I believe l3b is a much more recent variant, but I may be way off without looking it up.

 

However, neither approach alone would be a good indication of how the skin color used to be in our ancestor. Or specifically how dark it was, as all evidence points toward dark complexion. I am sure that there is actually lit about that somewhere, but I have not bothered digging them up yet. And frankly, my knowledge is too limited to be certain how accurate the estimates could be. The only things I can think of are studies that show a strong selection for sun-resistant MC1R alleles around the time of hair loss.

 

However, if we really want to use current populations as a kind of proxy how skin color may have appeared as a function of UV radiation, I refer you to Jablonski and Chaplin (2000, J human evolution) where they have gathered UV data and compared it with skin reflectance (as a measure of skin color) and clearly found darker complexions in higher radiation areas. Of course, the values won't fit perfectly as access to folates, clothing etc. will have modulated the selective pressures somewhat from what they used to be. But looking specifically at near-equator populations I think it is safe to say that our ancestors would have been rather on the darker rather than the lighter side.

Edited August 11, 2016 by CharonY

[John Cuthber]

 

The point wasn't missed, it was ignored as (IMHO) non sequitur.

 

Maybe a more constructive way of blowing my hypothesis out of the water would have been to refer me to something like 'Spectral Emissivity of Skin and Pericardium' (Steketee). From which I learn that the emissivities of pale and dark human skin in the mid-IR are not only equal, they are both phenomenally high. Much higher than water, higher even than black rubber and charcoal.

 

Now that is food for thought!

You didn't ignore it; you commented on it.

 

It was relevant to the point in response to which it was raised- your suggestion that dark skin radiates heat better.

do you remember this "one of the really useful benefits of a dark skin that I envy is the ability to find shade and radiate excess body heat away quickly, ,,,"

You were saying you envied them for their radiative cooling- but it's essentially the same rate of cooling as yours.

 

If you have a mixture of different things (and skin has) then you are likely to end up with something quite dark. It's like mixing paints as a kid. You were disappointed to find that you ended up with something that looked like mud.

[sethoflagos]

........However, if we really want to use current populations as a kind of proxy how skin color may have appeared as a function of UV radiation, I refer you to Jablonski and Chaplin (2000, J human evolution) where they have gathered UV data and compared it with skin reflectance (as a measure of skin color) and clearly found darker complexions in higher radiation areas. Of course, the values won't fit perfectly as access to folates, clothing etc. will have modulated the selective pressures somewhat from what they used to be. But looking specifically at near-equator populations I think it is safe to say that our ancestors will have been rather on the darker rather than the lighter side.

 

This is all very good informative stuff CharonY.

 

Going back to the OP, what struck me was an apparent underlying assumption that (and I paraphrase quite wildly here) 'If you come from the Albertine Rift your skin colour will be precisely RAL 8028 Terra Brown.'

 

Now I know no one used those precise words, and yet there seems to be a great deal of resistance to any suggestion from me that there may well have been significant variance in the skin tone of our ancestors. Whether as much back then as there is in tropical Africa today, is neither here nor there.as far as I'm concerned. But any suggestion that there was zero or even insignificant variance smacks of a less than scientific agenda.

 

As for the Bantu tribal group, yes I know a little, having been married to one for nearly 15 years. But then the Bantu expansion was a mere 3,000 years ago, coinciding with their discovery of iron smelting. Before that, their range was quite restricted. So extrapolating a stereotypically modern Bantu physiognomy back 200,000 years to being characteristic of all of humanity at that time seems a little far-fetched doesn't it?

 

I know these visual arts people have to pick something to go on, but surely we realise that the artistic license here may well exceed the scientific justification.

 

Or does it?

Edited August 11, 2016 by sethoflagos

[CharonY]

Actually I only brought up the Bantu expansion to elaborate on your haplogroup thesis. Specifically to elaborate that haplogroup L3e carriers are not necessarily as fair skinned (and also because we have a bit of an idea about their expansion). In contrast, the evidence suggest that populations that have stayed or originated recently near central Africa do have darker skin, which coincides with the UV/folate hypothesis. I.e. so far even in the confines of this thread we have evidence that pointing to darker skin color.

Under these assumptions the hue of the skin will be primarily driven between the needs of folate conservation and vitamin D3 synthesis. Considering the latter not to be limiting (and we find also evidence for this in lit) being darker would be a selective advantage (which follows the argument of Joplin's research).

[sethoflagos]

Actually I only brought up the Bantu expansion to elaborate on your haplogroup thesis. Specifically to elaborate that haplogroup L3e carriers are not necessarily as fair skinned (and also because we have a bit of an idea about their expansion). In contrast, the evidence suggest that populations that have stayed or originated recently near central Africa do have darker skin, which coincides with the UV/folate hypothesis. I.e. so far even in the confines of this thread we have evidence that pointing to darker skin color.

Under these assumptions the hue of the skin will be primarily driven between the needs of folate conservation and vitamin D3 synthesis. Considering the latter not to be limiting (and we find also evidence for this in lit) being darker would be a selective advantage (which follows the argument of Joplin's research).

 

 

Isn't there some new thinking about the significance of pigmentation to dermal D3 synthesis?

 

It's a moot point for us since childhood rickets remains fairly common in Nigeria and the Federal Government would very much like to eradicate it - the means and will are there.

 

But the old assumption that it was due to low intake of dairy products seems to be questioned by work such as Signorello LB, Williams SM, Zheng W, Smith JR, Long J, Cai Q, Hargreaves MK, Hollis BW, Blot WJ (2010). "Blood vitamin D levels in relation to genetic estimation of African ancestry".Cancer Epidemiology, Biomarkers & Prevention.