Bushmen

Affluence Without Abundance

gregladen — Mon, 03 Jul 2017 09:07:36 +0000

Affluence Without Abundance

My father in law is an excellent amateur mixologist. I don't drink alcohol very often, but we're all up at the cabins, so last night I had a paper plane. And I believe this is what led to a night of strange and extensive dreams, and in my dreams was my recently deceased PhD adviser, Irv DeVore. (Irv was not dead in the dream.) DeVore is famous for having initiated, with Richard Lee, the first scientific study of extant living foragers, and they worked with the Ju/'Honasi of Botswana/Namibia/South Africa.

So, it was strange to have the lingering dream on my mind as I opened the latest Science magazine to see a review, by Alan Barnard, of a recent and interesting book on those people: Affluence Without Abundance: The Disappearing World of the Bushmen.

A vibrant portrait of the “original affluent society”--the Bushmen of southern Africa--by the anthropologist who has spent much of the last twenty-five years documenting their encounter with modernity.

If the success of a civilization is measured by its endurance over time, then the Bushmen of the Kalahari are by far the most successful in human history. A hunting and gathering people who made a good living by working only as much as needed to exist in harmony with their hostile desert environment, the Bushmen have lived in southern Africa since the evolution of our species nearly two hundred thousand years ago.

In Affluence Without Abundance, anthropologist James Suzman vividly brings to life a proud and private people, introducing unforgettable members of their tribe, and telling the story of the collision between the modern global economy and the oldest hunting and gathering society on earth. In rendering an intimate picture of a people coping with radical change, it asks profound questions about how we now think about matters such as work, wealth, equality, contentment, and even time. Not since Elizabeth Marshall Thomas's The Harmless People in 1959 has anyone provided a more intimate or insightful account of the Bushmen or of what we might learn about ourselves from our shared history as hunter-gatherers.

Barnard says:

The book is full of illuminating observations from the Bushmen themselves. In one passage, for example, Suzman relates an encounter with ≠Oma, one of the resettlement community's most established residents, who once served as a foreman when Skoonheid was still a working farm: “If you are foreman,” ≠Oma tells Suzman, “then you are the eyes and the ears of the baas [boss] on the farm. You are the chief of the workers and are in charge when the baas is away.” Despite better pay and greater social standing among the white farm owners, ≠Oma never entirely succeeded in securing the respect and deference he demanded from his fellow Ju/'hoansi. Today's Bushmen are part of two worlds, one guided by the group's traditional commitment to egalitarianism and the other based on subjugation.

In general, anthropological commentary is kept to a minimum, but Suzman's descriptions are full of insight. “To them everything in the world is natural and everything cultural in the human world is also cultural in the animal world, and ‘wild’ space is also domestic space,” he writes, for example, in chapter 7. “So while Ju/'hoansi consider the litter to be an irritation, few see it as pollution—at least in the way the tourists do.”

Suzman's frequent reflexivity (e.g., “I never hunted with /I!ae. I was too clumsy, loud, and slow.”) makes the book far more interesting than typical accounts full of statistical detail, academic references, and the like. The book offers few references, and details are limited to those that make for good reading. There are, however, several useful (albeit simple) maps of the areas described and a brief explanation of how to pronounce clicks.

The review is here, but I'm not sure if you can see it without a subscription.

gregladen Mon, 07/03/2017 - 05:07

Tags

Africa

Kalahari

Bushmen

foragers

Hunter-gatherers

Ju/'hoansi

San

What average genetic variation can tell us (or not)

razib — Wed, 17 Feb 2010 22:30:43 +0000

What average genetic variation can tell us (or not)

To the left I've juxtaposed the images of the four Bushmen males whose genomes were analyzed in the recent Nature paper and compared to Desmond Tutu. I've added to the montage a photo of a Swedish and Chinese man. The Nature paper looked at the HapMap data sets which had within them whites from Utah, northwest Europeans, and Chinese from Beijing, and compared these populations to the Bushmen and Desmond Tutu. One important point that this paper emphasized was that the rule-of-thumb that African populations have the most extant genetic diversity of all human groups, and that the Bushmen have the most diversity of all (perhaps with the Pygmy groups of Central Africa), seems broadly confirmed:

In the 117âmegabases (Mb) of sequenced exome-containing intervals, the average rate of nucleotide differences between a pair of the Bushmen was 1.2 per kilobase, compared to an average of 1.0 per kilobase differing between a European and Asian individual.

In other words, genetic distance measured as nucleotide substitutions would show that two random Bushmen of this particular subgroup (see comment) are more disparate than two random European and Chinese individuals! But if you asked someone to cluster these individuals by phenotype I suspect they'd say that all the individuals in the first row belong together, while the two individuals in the second row are distinctive.

The reason for these peculiar total genome variation patterns are probably demographic. All non-Africans likely descend from one migration Out of Africa, so they carried with them only a small proportion of the total genetic variation of the ancient Africans because of the population bottleneck to which they were subjected. Those humans who remained in Africa were not subjected to the same extreme bottleneck, and so maintained more genetic variation. This likely explains the high genetic variance of Africans vis-a-vis non-Africans. As an analogy, consider the fact there is minimal regional accent variation in Australian English in relation to the variation in Britain; local dialects take time to emerge, and Australia is a recently settled region.

Another issue may be stabilizing selection for particular phenotypes, which result in the Bushmen lookingly relatively alike despite their varied genetic heritage when compared to the difference between the Swede and Han Chinese. Over the past 10-20 thousand years it seems as if there's been a lot of evolution of pigmentation in northern Eurasia. By contrast, the Bushmen have retained the ancestral genetic architecture of H. sapiens which results in a generally darker complexion. This ancestral genetic architecture is common across darker skinned populations, and is probably due to functional constraint. In other words, alleles which result in lighter skin tend to be purified from the gene pool by negative selection. The thick hair of East Asians is likely due to recent changes on the gene EDAR, while the pale hair and eyes of northern Europeans is due to a lot of evolutionary change on the pigmentation genes. For whatever reason many salient physical traits which we use to classify populations don't exhibit the pattern of the total genome, whereby all non-Africans are a branch of the tree of H. sapiens, which mostly consists of African lineages which are much more variegated. Likely new environmental selection pressures once populations left Africa play a role in this.

But there may also be other factors. Biological anthropologist Henry Harpending once explained to me that even if populations exchange genes regularly so as to become indistinguishable on their total genome content, there may be social selection for particular traits correlated with group membership. Harpending explained that on many neutral markers, such as mtDNA lineages, the Bushmen and their Bantu neighbors seem to be relatively undifferentiated. But when it came to physical appearance there was a sharp distinction. Why? Harpending suggested that perhaps there is a strong fitness advantage for someone of mixed ancestry to look more like the group they're born into. For example, imagine a Bushman man takes a Bantu wife, some of his children favor the father, some the mother. In terms of total genome content all the offspring reflect the parental populations, but on the subset of genes which control traits salient in marking Bushmen-Bantu differences (e.g., epicanthic eye fold) there may be greater fitness to those who carry genotypes which reflect the group into which they're born.*

Obviously genetics is fascinating to me, and probably you if you're reading this weblog. When applied to humans it has a very strong emotional impact, consider the popularity of genealogical companies which utilize genetic methods. But it is important to remember that our own intuitive model of our species is to some extent pre-scientific, and mapping colloquial concepts and preconceptions onto scientific findings can result is less than perfect clarity. In this, the 1980s hullabaloo over mitochondrial Eve served as simply a foretaste of what was to come.

* As a toy example, imagine that the epicanthic eye fold is monogenic, controlled by a locus which comes in two flavors, E & e. Those with EE have the fold, those with ee do not, while those with Ee are somewhere in the middle. Imagine that the Bushmen have very high frequencies of EE, while their Bantu neighbors have lower frequencies of the E allele, but not trivial. Imagine if a Bantu woman is of the genotype Ee, while her Bushmen husband is EE. 50% of the offspring would exhibit the Bushmen epicanthic eye fold phenotype. In terms of total genome content these individuals would be no more Bushmen than their Ee siblings, but they would look more Bushmen to others of the tribe, and so might have more success finding a mate due to lower levels of social exclusion. Extrapolate this process generally and you can see how genes which control outwardly salient traits may exhibit more between group difference than the overall genome.

razib Wed, 02/17/2010 - 17:30

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I don't follow.

In particular what I'm not clear on is whether this paper offers evidence of a serious liklihood of there having been separate groups of Bushmen who rarely swapped genes over the course of the past hundred thousand years.

All other possibilities for the high varietion levels aside, does it really seem reasonable to believe that such small communities survived relatively endogamous for thousands of generations? I was of the vague impression that the only remaining "ancient" groups were one or two pygmy ethnicities and one or two Bushmen ethnicities. How wrong does this appear to be? (I'm biased and hope you're going to say "very wrong", because that would just be hellishly romantic. Imagining that the ancient pre-Out-Of-Africa diversity is still with us is astonishing. Fuck, the example of the Samaritans makes my imagination run wild, and here we're talking about peoples twenty times as ancient.)

Good synopsis. Though one thing really strikes me in all this. If we were not talking about humans, this would be a completely mundane story of a relatively recent radiation.

travc,

Spot on. That's why I love it so. The more we look "under the skin" the more we realize (I hope) how artificial and pointless are the surface classifications we've developed.

But if you asked someone to cluster these individuals by phenotype I suspect they'd say that all the individuals in the first row belong together, while the two individuals in the second row are distinctive.

You could have thrown in a Bantu, a New Guinea highlander, and a Malay and most people would have put them in with the Bushmen, because most people's folk ethnologies code by color using the 3-color (rarely 5-color) typology.

You could have thrown in a Bantu, a New Guinea highlander, and a Malay and most people would have put them in with the Bushmen

A recent example is Tiger Woods and Barack Obama. They are identified as black (solely on the basis of one parent even though the other parent was of a different race).

most people's folk ethnologies code by color using the 3-color (rarely 5-color) typology

It's also a social construction too in my view. We have also been socialized to think of Tiger Woods and Barack Obama as black because in reality these men actually do appear to be mixed and not wholly black. It's nothing to think hard about, really..

The Bushmen & the Bantu

razib — Wed, 17 Feb 2010 12:13:35 +0000

The Bushmen & the Bantu

There's a new paper out in Nature which details the genomes of several Bushmen, and how they relate to other humans, and one particular Bantu speaking individual, archbishop Desmond Tutu. It's open access, Complete Khoisan and Bantu genomes from southern Africa. I haven't read the whole thing, but it is probably best to check out Ed Yong's very thorough review first. Here's an interesting point Ed brings up:

Most surprising of all, many of their unique SNPs are actually fairly recent developments. The Bushmen are one of the oldest human groups on the planet and you might expect their genes to reflect humanity's most ancestral state. But not the SNPs - Schuster found that only 6% of !Gubi's newfound SNPs matched the equivalent sequences in the chimpanzee genome; by comparison, the same positions in the human reference genome are an 87% match for the chimp one. They can't be ancestral sequences. They must have turned up after the Bushmen dynasty diverged from other human populations, and they provide hints about the history of this most ancient of human lineages.

The paper itself uses the phrase "the oldest known lineage of modern human." It's pretty ubiquitous as a description for the Bushmen and related peoples. But as you probably know, I don't think it's that helpful, though the usage of the term "lineage" makes the topology of the phylogenetic tree clear at least. Perhaps more evidence of derived alleles in "ancient populations" will shift the definitional ground a bit....

Citation: Schuster et al., Complete Khoisan and Bantu genomes from southern Africa, doi:10.1038/nature08795

razib Wed, 02/17/2010 - 07:13

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So "most divergent lineage" would be a more accurate way to phrase it?

(I fixed some typos etc.)

Quality press knew how to find the relevant angle to that story.

Associated Press, Archbishop Tutu's DNA helps show African diversity:

"We are all very, very similar to one another," Schuster said. Gibbs said the DNA differences discovered in the African subjects can't be used to support racist arguments. He noted that DNA diversity within a continent is greater than the differences between continents. The study found, in fact, that Bushmen are as different from a previously studied Yoruba man in Nigeria as a European man is.

Reuters, African gene trawl may provide secrets to long life:

"On average we found as many genetic differences between two Bushmen than between a European and an Asian," said Dr. Vanessa Hayes of the University of New South Wales in Australia, who worked on the study reported in Thursday's issue of the journal Nature. "This research now provides us with the tools to read the story of human evolution and specifically the story of disease evolution."Geneticists have long known that, on the level of DNA, there is no such thing as race.

FAZ (a German broadsheet), A Blessing for the Genome (doesn't make much more sense in the original German):

As we now know, two Bushmen from the Kalahari Desert are more different from each other genetically than a European from an Asian. In other words: ethnic groups and races are smoke and mirrors by the standards of genetic research. Could there be a more wonderful reassurance in the fight against apartheid, that powder keg?

"Oldest human group" makes little sense. They are just as old as any other human group - the same amount of time has passed since all human groups last shared a common ancestor with each other, with chimps, or with any other species.

"Most divergent lineage" implies that they have evolved (diverged) more than other human lineages. No evidence of that.

Not crazy about "oldest known lineage" because again it indicates that they are somehow older, although use of the word lineage is a little closer. Really, the correct phrase would be "earliest diverging lineage."

I suppose that this looks like very nitpicky use of jargon to many non-phylogeneticists, but these incorrect descriptions of the Bushman lineage feeds directly into this all-too-commonplace expectation that their genes are going to reflect "humanity's most ancestral state," that they are somehow more primitive, etc. etc. The phylogeny says nothing of the sort.

Three of the four Bushmen are from the same group, speakers of the Northern Bush
language. The fourth is identified as a "Tuu" speaker, apparently from Gobabis. All the Bushmen I have ever met around Gobabis are also Northern Bush. Some of them identify as "!xu" (low tone), the origin I suppose of the name "!Kung", and my bet is the "Tuu" is just "!xu".

They ought to have gotten some folks from some of the other Bushman groups, whose languages have no apparent relationship at all to !Kung (or whatever we call them this year) save for the presence of clicks.

@Anon - No, not nitpicky at all. I found your explanation very helpful. Don't stop.

Africa's genetic diversity revealed by full genomes of a Bushman and a Tutu

edyong — Wed, 17 Feb 2010 12:00:59 +0000

Africa's genetic diversity revealed by full genomes of a Bushman and a Tutu

Meet !Gubi, the tribal elder of a group of Bushmen (or Khoisan), one of the oldest known human lineages. He lives the life of a hunter-gatherer in the Namibian part of the Kalahari Desert. But he also has a strange connection to James Watson, the ~~British~~ American scientist who helped to discover the structure of DNA. For a start, they're both around 80 years old. But more importantly, they are two of just 11 humans to have their entire genomes sequenced.

Along with Archbishop Desmond Tutu, !Gubi is one of two southern Africans, whose full genomes have been sequenced by Stephan Schuster and an international team of scientists . Schuster's team also analysed the genes of three other Bushmen - G/aq'o, D#kgao and !AÄ±Ë (see footnote for pronunciation guide) - focusing on the parts of their genome that codes for proteins. Like, !Gubi, these men are tribal elders and all are around 80 years old. Despite the fact that the four Bushmen come from neighbouring parts of the Kalahari, their genetic diversity is astounding. Pick any two and peer into their genomes and you'd see more variety than you would between a European and an Asian.

This diversity reveals just how important it is to include African people in genome sequencing projects. Until now, the nine complete human genomes have included just one African - a Yoruban man from Nigeria. The rest have hailed from Europe, America, China, Korea and, most recently, Greenland circa 4,000 years ago. This is a major oversight. Africa is the birthplace of humanity and its people are the most genetically diverse on the planet. To understand human genetics without understanding Africa is like trying to learn a language by only looking at words starting with z.

The Bushmen certainly provide a glimpse into this diversity. Desmond Tutu was also selected because his ancestry covers the two largest of southern Africa's Bantu groups - the Tswama and the Nguni - making him an excellent representative for many southern Africans. Vanessa Hayes, who worked on the study, says, "This work is very expensive so we wanted to maximise the amount of diversity we could get in one individual." The team had other reasons for sequencing the bishop."He's a voice for southern Africans and for his people. He's a chairman of the Global Elders. He provides a genome with a lot of medical history behind it, having survived prostate cancer, polio and Tb, diseases that affect many southern Africans." But most importantly, Hayes says, "He wanted to participate. He himself wanted to study medicine so this for him was a personal endeavour."

The researchers hope that their new data will allow medical research to become more inclusive. Vanessa Hayes, who led the study, says that she found HIV research in South Africa to be very difficult because most genetic databases are severely Eurocentric, which rules out a lot of Africans from medical research. Without this knowledge, for example, we have no way of knowing if a drug that was developed and tested in Western patients will have the same benefits and risks in African ones.

Schuster and Hayes compared the two new African genomes to the reference version (a composite of several anonymous people) and looked for "single nucleotide polymorphisms" - places that differed by a single DNA letter. He found these "SNPs" in their hundreds of thousands. Both !Gubi and Tutu have around a million unique SNPs that they don't share with each other or any of the other fully sequenced humans. Likewise, the proteins of the five Africans had over 27,000 amino acids that differed from the reference sequence, around half of which are unique to them.

Some of these differences are easily explained by the Bushmen's lifestyle, reflecting adaptations to hunting and gathering in a hot, dry climate. Being dark-skinned hunter-gatherers, all of them lack genetic variant that give Europeans light-coloured skin and allow them to cope with eating dairy products.

All of the Bushmen had a version of the vitamin D receptor that is associated with denser bones and three of them have a variant linked to better sprinting performance. Some of the SNPs grant the carrier the ability to taste bitter plant chemicals, and hunter-gatherers would certainly find it useful to avoid toxic plants. One of !Gubi's variants could allow him to break down foreign substances or resist parasites. Another might make his kidneys better at reaborsbing vital chloride ions and reduce the loss of salt and water, an important skill when you live in the scorching desert.

Other differences are perhaps more surprising - the five Africans all lack a genetic variant that is specific to Africa and that grants resistance against malaria. It's possible that the Bushmen may not need such resistance. But that could well change as their populations dwindle and they become forced into agricultural lifestyles, which carry higher risks of disease. Again, these newfound genetic markers could allow scientists to watch how they adapt to such challenges at a genetic level.

Most surprising of all, many of their unique SNPs are actually fairly recent developments. The Bushmen are one of the oldest human groups on the planet and you might expect their genes to reflect humanity's most ancestral state. But not the SNPs - Schuster found that only 6% of !Gubi's newfound SNPs matched the equivalent sequences in the chimpanzee genome; by comparison, the same positions in the human reference genome are an 87% match for the chimp one. They can't be ancestral sequences. They must have turned up after the Bushmen dynasty diverged from other human populations, and they provide hints about the history of this most ancient of human lineages.

The south African genomes will also make geneticists re-evaluate what they know about how our genes affect our health and risk of disease. Our current knowledge in this area is incredibly biased towards Western societies and the results of studies in such populations don't always translate to other continents. For example, one of the Bushmen had a SNP that is reputedly linked to Wolman's syndrome, a disease that prevents people from storing fat properly and kills at a young age. Try telling that to the eighty-something gentleman! Hayes says, "!Gubi is a very fit and healthy man and much better skipper on a skipping rope than I am

Reference: Schuster, S., Miller, W., Ratan, A., Tomsho, L., Giardine, B., Kasson, L., Harris, R., Petersen, D., Zhao, F., Qi, J., Alkan, C., Kidd, J., Sun, Y., Drautz, D., Bouffard, P., Muzny, D., Reid, J., Nazareth, L., Wang, Q., Burhans, R., Riemer, C., Wittekindt, N., Moorjani, P., Tindall, E., Danko, C., Teo, W., Buboltz, A., Zhang, Z., Ma, Q., Oosthuysen, A., Steenkamp, A., Oostuisen, H., Venter, P., Gajewski, J., Zhang, Y., Pugh, B., Makova, K., Nekrutenko, A., Mardis, E., Patterson, N., Pringle, T., Chiaromonte, F., Mullikin, J., Eichler, E., Hardison, R., Gibbs, R., Harkins, T., & Hayes, V. (2010). Complete Khoisan and Bantu genomes from southern Africa Nature, 463 (7283), 943-947 DOI: 10.1038/nature08795

A note on names: The ~~Bushman language~~ Bushmen languages includes a variety of clicks, which explains the strange characters in their names. The # is an alveolar click, made by pulling the tip of the tongue down sharply from the roof of the mouth to make the sound of a popping cork. The ! is a palatal click, which is a softer version of the alveolar one and made with a flat tongue. The / is a dental click, which is made by sucking air through the front teeth and sounds like an English tsk!

Another note on names: I'm aware that there's controversy over the use of the term "Bushmen" in some circles. I'm using it because it's by far the most commonly used term in the paper, which also mentions San or Khoisan. Note the captial B to denote an actual group of people rather than a colloquial descriptor.

More genomics and anthropology:

edyong Wed, 02/17/2010 - 07:00

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Ed what is your take on this statement with respect to the position of at least one science blogger that there is no evidence of genetic determinants for athletic performance (and that the very idea is a thinly-veiled cover for racism):

"All of the Bushmen had a version of the vitamin D receptor that is associated with denser bones and three of them have a variant linked to better sprinting performance."

I'd say that some of these SNP associations aren't exactly conclusive and this study, if anything, confirms that. The sprinting thing was mentioned in the paper, which is why I mention it here. Worth noting that the authors themselves cite the uncertainty of some of these associations - will drag
out actual quote when I get to a computer.

Great stuff. Re "only 6% of !Gubi's newfound SNPs matched the equivalent sequences in the chimpanzee genome; by comparison, the same positions in the human reference genome are an 87% match for the chimp one. They can't be ancestral sequences."

Could the reference genome be ancestral, and this man have a derived sequence?

and you might expect their genes to reflect humanity's most ancestral state. But not the SNPs - Schuster found that only 6% [â¦] matched the equivalent sequences in the chimpanzee genome

Of course, the present state of the chimpanzee genome isn't the same as the state our last common ancestor had some 6 million years ago. It's not like mutation and drift, or even selection, had stopped for chimps.

The Bushman language

It's a large, large language family, easily comparable to Indo-European at the very least.

Another note on names:

It being a language family, there's no self-designation for the whole family in any of the languages. So we can't just "call them what they call themselves"â¦

"Khoisan" is a term for the language family formed by the Kxoekxoe (Hottentot) and, well, Bushman language families. That name is an artificial composite of "Kxoekxoe" and "San".

adaptations to malaria in africa are pretty recent on an evolutionary scale. i think on the order of 5,000 or so. no surprise that hunter-gatherer peoples lack the variants.

Could the reference genome be ancestral, and this man have a derived sequence?

Of course, but probably both are derived to varying extents.

Re Khoisan not having the malaria adaptations: malaria is simply not widespread in South Africa, so the relevant selective pressures probably didn't operate too strongly. See: http://www.sa-venues.com/malaria-risk-areas.htm

Not only have chimps obviously evolved somewhat since our divergence with the last common ancestor (although not nearly enough to account for only 6% similarity! Even 87% is a bit low...) but the state of the chimp genome within the databases is a bit miserable. The assembly is simply wrong in some places.

James Watson is British?

Aw hell. You can tell I wrote this in a rush, can't you? Fixed the "Bushman language" thing and Watson's nationality. Thanks to everyone for the constructive feedback.

What does it mean for a SNP to 'match' since a SNP is a locus at which there is variation. Presumably one allele or the other is ancestral at every SNP.

The 'old lineage' stuff doesn't quite seem sensible either. Pick an allele at a locus from me, an allele from the same locus from a Bushman, follow them back to their common ancestor. The length of the two branches, hence the probability of a mutation have happened is exactly the same on each branch. Hence the probability of the ancestral state (or the expected frequency of the ancestral state if we extend the sample of size 2 to larger samples)is exactly the same in both of us. Alan Rogers recently published a nice paper showing this in greater detail.

Genetic diversity increases where there is low selection pressure. Africa has a mild climate without seasonal food scarcity. It is also true that the founder effect decreases genetic diversity the farther a population migrates from their origins.

With regard to African athletic performance, the prevalence of myostatin mutations ranges from ten to twenty percent in Africa, while only 1% in Europe and Asia. As well the slavers culled for heavily muscled slaves because they fetched a better price and were more likely to survive the arduous journey bound and shackled, stacked like cordwood in the hold of a ship.

One interesting implication (not quite enough data for a result, yet) is that this group has managed to avoid inbreeding.

It seems pretty common to assume aboriginal groups (especially when they have small populations today) were somehow always isolated. Logically, that should be the exception, not the rule, since inbreeding isn't exactly a good thing for the long term success of a population. Yeah, the exceptions are cool simplified cases we can make more interesting conclusions about, but again, not the rule.
Maybe we still have too many geneticists trained on lab strains.

Also, as I mentioned elsewhere, these results seem to be exactly what we should expect for a species which has undergone a recent radiation. We've seen the same sort of thing numerous times in other clades.

I think that you will find that Archbishop Tutu is of Twsana, not "Twsama" origen.
I also question "scientist's" description of "Africa" having a mild climate. Africa is a very large continent with a huge variety of climatic zones. Even just in Southern Africa you have the mediterranian climate of the southern Cape, the tropical climate of northern Kwazulu-Natal and Mozambique, the velt of the central plateau and the extreme desert of the Namib. It is also subjected to periodic drought conditions that have waxed and waned based on oceanic and climate cycles. I can assure you that the Kalahari where the majority of the San peoples live is in no way a mild climate. Extremely hot with very scarce water and major fluctuations of food availability based on animal migrations and a growing season based on the very seasonal rains. I agree with the authors of the study that the genetic diversity is primarily based on the age and ancestral nature of the populations rather than relaxed selection pressure. Having spent a considerable amount of time out in the Southern African bush including the kalahari I challenge anyone who things that the climate and selection pressure are "mild" to live like the San peoples do for a month...

It's a large, large language family, easily comparable to Indo-European at the very least.

If at all. Isn't it more of a convenient cultural/geographical lumping?