Joined: 02 May 2006 {Posts: 444 } Location: Île-de-France
Posted: Wed 28 Jan 2009 11:16 Post subject: Distance from Africa explains phenotypic diversity
Wasn't sure if this should go here or Molecular Anthropology-the focus is on skull measurements, although genetic markers are compared with their results.
Quote:
Distance from Africa, not climate, explains within-population phenotypic diversity in humans
Abstract: The relative importance of ancient demography and climate in determining worldwide patterns of human within-population phenotypic diversity is still open to debate. Several morphometric traits have been argued to be under selection by climatic factors, but it is unclear whether climate affects the global decline in morphological diversity with increasing geographical distance from sub-Saharan Africa. Using a large database of male and female skull measurements, we apply an explicit framework to quantify the relative role of climate and distance from Africa. We show that distance from sub-Saharan Africa is the sole determinant of human within-population phenotypic diversity, while climate plays no role. By selecting the most informative set of traits, it was possible to explain over half of the worldwide variation in phenotypic diversity. These results mirror those previously obtained for genetic markers and show that ‘bones and molecules’ are in perfect agreement for humans.
Clarification. It only addresses intra population variation.
Andrea Manica clearly stated that the paper referred to within population diversity, not continental diversity The debate that got me suspended made me research the subject even further. I still disagree with Frank. I just have more evidence that I was right.
I’ll add email from discussions I have been having with various anthropologists.
First, my original question:
Salsassin wrote:
I keep on hearing that Africa has the most genetic variability so that it also encompasses the most phenotype variability.
I am curious if this really adds up as so many other factors other than genetic mutations occurring play a role on phenotype survivability in a population. Doesn’t environment play a big role?
I am curious, if you compare all of Africa for phenotypic diversity: skin tone extremes, craniofacial variability, size and weight, hair types, body proportions, etc, to that of the entire OOA Diaspora, from Europe, to Asia, to the Islands, to Australia, to Native America, with all those changes in environment, does Africa really have a larger variation of phenotypes? My common sense says no, but I was hoping you could give me a scientific explanation why or why not, as to my conclusion.
I just don’t see that much phenotype variability in Africa to encompass that of the rest of the world.
John Relethford wrote:
Good question, but the genes/traits that are used in such studies are most frequently neutral traits - those not affected by natural selection, or minimally affected by natural selection WITHIN populations. Selection would affect variation AMONG populations for some traits (e.g., skin color) but does not appear to affect the amount of variation within populations.
Variation within populations is a function of both age (populations that are older have accumulated more mutations) and population size (smaller populations experience more genetic drift, which reduces diversity). The environment probably enters in here indirectly, as most archaeologists suggest that environmental conditions during hunting and gathering times would have limited population size/density in many parts of Eurasia, relative to Africa.
If you compared the phenotypic variation in Africa with phenotypic variation in all non-African groups combined, you would probably not see African variation encompassing the variation in the rest of the world, but that is not what studies of within-group variation are saying. Variation among groups is a different phenomenon than variation within populations. The first refers to how groups differ from each other on average, whereas the second refers to how individuals in a group are different from the average of that group. If you ever took a statistics class and computed something called an ANOVA (Analysis of Variation), you computed variation among the groups and within the groups. If not, the last sentence is probably as clear as mud!
Luigi Cavalli Sforza wrote:
I think your doubt is quite reasonable, but average genetic data calculated on a large proportion of the genome (at least of the variable part) indicate a very precise decrease of genetic diversity with the geographic distance of indigenous populations from the place of origin of humans in east Africa, In fact this correlation, which is due to drift is so precise that superficially it seems to leave little space for thinking that natural selection is so important, perhaps only 20% of all the genetic diversity in the rest being fue presumably to drift (Ramachandran et al,.2005 , PNAS 102: 15942). We, All humans including scientists are very impressed by external phenotypic differences, the only ones that are clearly visible to us, and that depend in a large measure on climate differences. In a very early paper (Proceedings of the IX intl, congress of Genetics at The Hague, 1963,) using microsatellites, confirmed on full genome snips data) we show that if you reconstruct evolution from anthropometric data you get a different picture .from that obtained with genes, and later work has confirmed that anthropometrics (both phenotype and genotype) are affected by natural selection due to climate. This is true also for all animals. While genetic data indicate a west to east difference , anthropometric differences depend on latitude differences..
David Bulbeck wrote:
I guess that claim about phenotype variability would depend on how you defined it, what you were looking at. Don’t forget that when organisms expand into new niches so selection pressures would favour greater visible phenotypic variation, whereas if they stay in their old niche phenotypic variation would tend to be of the less visible kind. E.g. frogs, which have huge genetic differences because they are so ancient, are kind of restricted to a particular design and so look less different from each other than, say, mammals which are genetically all much closer to each other than different genera of frogs.
I actually took one example by Hanihara who studied Cranio facial variations related to facial flatness, to see how Africa compared to the rest of the world:
OOAD is the Out of Africa Diaspora
Alveolar Index Range
OOAD
12.5
Islands
11.8
Africa
11.3
Eurasia
6.4
Americas
4.1
Chord Subtense Index Range
Eurasia
6.9
OOAD
6.9
Americas
4.4
Islands
4.4
Africa
3
Infraglabellar knotch Range
Islands
2.1
OOAD
2.1
Americas
0.9
Eurasia
0.9
Africa
0.5
Sagittal Frontal Index Range
OOAD
4.1
Islands
3.7
Eurasia
3.1
Americas
2.7
Africa
1.9
Simotic Index Range
Eurasia
29.1
OOAD
29.1
Africa
25.8
Islands
19.4
Americas
10.3
Zygomaxillary index Range
Islands
9.9
OOAD
9.9
Eurasia
8
Americas
5.2
Africa
4.2
In none does Africa have a larger variability than OOAD and in quite a few Eurasia has a larger variability than Africa.
Maybe in phenotypes that are less affected by environment and with less plasticity you will see a larger African range than the Diaspora, but there are plenty of phenotypes which are affected by the environment and that are more variable outside Africa.
The debate that got me suspended made me research the subject even further.
1. ?? Please explain. What "debate" got you suspended? Please give the thread number.
2. You are apparently presenting a thesis to be argued--something to do with genetic variation and diversity. Other than that it comprises mostly appeals to authority, it is unintelligible. Per rule 3.6 and its sub-rules, please state your thesis, preferably in a single sentence. First warning.
The debate that got me suspended made me research the subject even further.
1. ?? Please explain. What "debate" got you suspended? Please give the thread number.
2. You are apparently presenting a thesis to be argued--something to do with genetic variation and diversity. Other than that it comprises mostly appeals to authority, it is unintelligible. Per rule 3.6 and its sub-rules, please state your thesis, preferably in a single sentence. First warning.
My theses? LOL
Here it is:
There is no conclusive evidence that Africa has more interpopulational phenotypic diversity than the out of Africa Diaspora, as you claimed.
And all my communications with anthropologists and geneticists who have studied the phenomena have brought up no such evidence. Now you DID state such a claim as a statement of fact. But you never provided any such conclusive evidence.
In craniofacial variability, based on the Hanihara study, it is clear that at least, in that realm, in that study, Eurasia had more variability than Africa.
There is no conclusive evidence that Africa has more interpopulational phenotypic diversity than the out of Africa Diaspora, as you claimed.
Thank you. Please give the thread number where I claimed the contrary.
Also, you now have 24 hours to provide the thread number where you were previously suspended for presenting that thesis. Please try to understand. You made a factual claim (that this "debate got you suspended"). Per rule 3.2, you must now back up that claim with a source or face suspension. Second warning.
Joined: 07 Oct 2007 {Posts: 248 } Location: United States
Posted: Mon 13 Apr 2009 23:38 Post subject:
Interesting. So saying that Africans are more genetically diverse than non-Africans (on a continental basis) is not equivalent to saying that Africans have a greater range of phenotypes than non-African groups? In other words, physical diversity that is most obvious does NOT have as much to do with with distance from East Africa as say latitude and climate?
There is no conclusive evidence that Africa has more interpopulational phenotypic diversity than the out of Africa Diaspora, as you claimed.
Thank you. Please give the thread number where I claimed the contrary.
Also, you now have 24 hours to provide the thread number where you were previously suspended for presenting that thesis. Please try to understand. You made a factual claim (that this "debate got you suspended"). Per rule 3.2, you must now back up that claim with a source or face suspension. Second warning.
I know you. So I know I will be suspended again.
http://thestudyofracialism.org/viewtopic.php?t=5145
The fact is you defended the thesis that Africa has more phenotype diversity. You made a claim of skin color and then rationalized that Sub Saharan Africa was somehow more diverse in skin tone. Sorry, but Eurasia, and even just Asia still spans a larger parameter of skin tones per Jablonski. So your focusing on my arbitrary claim on height was a double standard considering your double standard when applied to your arbitrary claim of skin color.
Some things that were noted through correspondence from that study:
100% of world variability in stature, nasal height and lip height, 92% of world variability in nasal breadth, 80-90% of world variability in arm length, shoulder and hip breadth, head length, face height, facial index and nasal index. {The author} mention such things as hair form, and notes that, although no sub-Saharan Africans have straight hair like Mongoloids, in north-east Africa (Somalis, Afar) hair like Europeans and Indians is frequent; again, while no sub-Saharan peoples have skin color as late as northern Europeans, skin reflectance is quite high in some peoples: only 23% in eastern Bantu, but 43% in Kalahari Bushman (cf 64% in northern Europeans).
The questions I would have regarding this study, is how up to date the information was. It would be interesting to see if modern data still replicated these percentages. The second question would be to find out what percentages the Out of Africa Diaspora, and even just Eurasia encompassed, i.e. % world variability in stature, nasal height, lip height, nasal breadth, arm length, etc.
Looking at some modern studies:
Phenotype variation intra population is greater in Africa than anywhere else according to the study by Dr. Andrea Manica( The effect of ancient population bottlenecks on human phenotypic variation, Nature 448, 346-348 (19 July 2007)). Per his clarification, his study only applies to intra population variability and is not a claim of a comparison of variability at the continental level. (Great study, by the way).
In terms of phenotypic diversity {in between continents, or between Africa and the OOA Diaspora} things are not so clear in the most obvious features (e.g. brown eyes, dark skin and hair are predominant in Africa) so one could argue that Eurasia has greater variation in those features. Africa does have great variation in body size and shape, but perhaps no greater than the Americas or Eurasia. But it does seem to hold for things like the Howells cranial measurements, and for dental morphology.
We discussed how some cranio-facial features, at least, based on the Hanihara facial flatness, did not have a larger range in Africa. In that case the OOAD surpassed Africa in all the ranges of facial indexes, and Eurasia surpassed Africa in all facial features measured except for the alveolar index.
Per Dr. John Relethford's excellent study, Global Analysis of Regional Differences in Craniometric Diversity and Population Substructure - Human Biology 73:5 Human Biology 73.5 (2001) 629-636, we garner that "Both methods for estimating regional diversity show sub-Saharan Africa to have the highest levels of phenotypic variation, consistent with many genetic studies. Polynesia and the Americas both show high levels of regional diversity when regional aggregates are used, but the lowest mean local population diversity." This is consistent with Dr. Manica's study. The question would be how Africa compared to all other regions aggregated, and I would also be curious how Africa compared against just Eurasia."
The genes/traits that are used in such studies are most frequently neutral traits - those not affected by natural selection, or minimally affected by natural selection WITHIN populations. Selection would affect variation AMONG populations for some traits (e.g., skin color) but does not appear to affect the amount of variation within populations.
If you compared the phenotypic variation in Africa with phenotypic variation in all non-African groups combined, you would probably not see African variation encompassing the variation in the rest of the world, but that is not what studies of within-group variation are saying. Variation among groups is a different phenomenon than variation within populations.
Other studies look at differences between groups, and those differences (for neutral traits) correlate with the geographic distance between groups.
So these studies are predominantly speaking of intra group variability and do not deal with continental variability or only look at neutral traits, not those that can be most affected by environment (which would be important to my question of overall variability kind of like Hiernaux did (although we do not know how the Diaspora compared based on his study))
Some factors that seem to play a role:
Environment {plays a role}, but it is limited to those characters, which have phenotypic plasticity. Stature is the most obvious of these; skin color is another, but it is not too hard to tell whether tanning has played much of a part. A study of Aborigines at a desert settlement, Yuendumu, both those who had been born in the settlement and those who had led nomadic lives as children, found some differences in face shape according to what were probably the effects of greater or lesser use of chewing muscles -- but they were not all that great.
{Also} the longer the history of a human population, the larger population size, and the more environmental variation, we will have more phenotype variability because more people mean more mutations for natural selection in the diverse environments to work with.
{Also} phenotype variability would depend on how you defined it, what you were looking at. When organisms expand into new niches so selection pressures would favor greater visible phenotypic variation, whereas if they stay in their old niche phenotypic variation would tend to be of the less visible kind. E.g. frogs, which have huge genetic differences because they are so ancient, are kind of restricted to a particular design and so look less different from each other than, say, mammals which are genetically all much closer to each other than different genera of frogs.
Form these two comments I garnered that phenotypes that are more selective by environment and give an environmental survival benefit would be more variable in the Diaspora, while phenotypes that where more neutral to the environment, but could give other benefits, might be selected for in the stasis environment (Africa in this case).
{It would seem that} the external phenotypic differences, the only ones that are clearly visible to us, and that depend in a large measure on climate differences {are the most affected in the Diaspora}. In a very early paper (Proceedings of the IX intl, congress of Genetics at The Hague, 1963,) using microsatellites, confirmed on full genome snips data) we showed that if you reconstruct evolution from anthropometric data you get a different picture from that obtained with genes, and later work has confirmed that anthropometrics (both phenotype and genotype) are affected by natural selection due to climate. This is true also for all animals. While genetic data indicates a west to east difference, anthropometric differences depend on latitude differences.
So basically some physical traits are more plastic and affected more by environment and this would be more diverse in the Diaspora with it's larger populations and larger variety of environments.
So would it be safe to say that we really don't know if Africa or the OOAD (or even Eurasia for that matter) has a larger phenotypic variability(or at least on the visible side that most people use to visually classify people)? Of course I am only speaking in terms of modern humanity and not incorporating archaic humans.
For craniofacial comparisons, I have been recommended to use Howells, database, so I might try to explore that. Not sure where I would get data for such information such as femoral length, brachial and crural indices, etc.
He is also claiming Humans 160 kya looked just like humans today.
That is false.
Hofmeyr Skull 35 kya, Herto (Homo Idaltu) Skull, 160 kya.
http://thestudyofracialism.org/viewtopic.php?p=37338#37338
The robusticity in the craniofacial structure is not replicated in any human alive today.
Howell's database revealed the same diversity as Hanihara where the Diaspora had more variability than Africa.
Interesting. So saying that Africans are more genetically diverse than non-Africans (on a continental basis) is not equivalent to saying that Africans have a greater range of phenotypes than non-African groups? In other words, physical diversity that is most obvious does NOT have as much to do with with distance from East Africa as say latitude and climate?
Well, based on most of my discussions on the subject, intrapopulation wise, Africa is more variable at the local level. But not at the multipopulation level and definitely not on the continental level.
At least not in the most plastic of features. Like craniofacial variation and skin color. Those seem to be affected by climate and population size a lot more.
Just the islands of the world have more variation craniofacially than Africa does. Living Africa, that is.
When Africa was the most densely populated region of the world, it was much more variable it seems.
Joined: 07 Oct 2007 {Posts: 248 } Location: United States
Posted: Tue 14 Apr 2009 05:38 Post subject:
Salsassin wrote:
Well, based on most of my discussions on the subject, intrapopulation wise, Africa is more variable at the local level. But not at the multipopulation level and definitely not on the continental level.
Ah...Understood. Just so that it's clear, exactly what is "local" anyway? One ethnic group?
Yes, I support the thesis that Africa has more genetic diversity. But I do not use the words "conclusive evidence" because nothing in science is conclusive. Every conclusion can change when new evidence is presented. And I do not refer to "phenotype" (which to you apparently means craniofacial traits) because I consider craniofacial anthropometry too vague for objective measurement. I stick to DNA.
You are apparently convinced, from craniofacial anthropometry, that there is more diversity outside Africa than inside Africa. So be it. The very reason that this site has a forum on craniofacial anthropometry is so that its adherents have a place to post. You have never been suspended for expressing a thesis with which I disagree.
You have been suspended for refusing to back up implausible claims with sources. Instead, each time that you have been challenged to provide a source you have reacted by attacking the administrator or moderator. Even now. You say that you were once suspended for holding a thesis with which I disagree. This accuses me of intellectual dishonesty, something that I take seriously.
Twice I have asked you to back up this claim, to show when you were ever suspended for presenting an unlikely thesis. Twice you have refused to do so, arguing instead: (1) that my thesis about genetic diversity is in error (which could well be true—I am often in error), (2) that I refuse to provide sources (not true, I am always happy to give sources), and (3) that I suspend those with whom I disagree, thus merely repeating the same claim.
Salsassin wrote:
I know you. So I know I will be suspended again.
Yes. I am unhappy to do so because I believe that you have much to offer this site. But you seem to enjoy conflict more than civil debate. And so, I must conclude that this is not the best website for you.
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