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paleoanthropology, genetics and evolution

population growth

  • Agriculture, population expansion and mtDNA variation

    Mon, 2011-05-23 11:50 -- John Hawks

    Earlier this spring, I wrote about a paper by Brenna Henn and colleagues that presented new data on SNP variation in recent African hunter-gatherer populations [1] ("Population structure within Africa: has 'modern human origins' become a non sequitur?").

    Another paper that came out this spring from the same research group is also very interesting. Christopher Gignoux, Henn and Joanna Mountain [2] examined the evidence for Holocene population growth in Europe, Africa and Southeast Asia, from within-haplogroup variability of mtDNA haplogroups. The idea is that earlier samples were not finely resolved enough to examine events of the last few thousand years, either because they included only small sequences (e.g., control region) with limited variation, or because they included whole mtDNA genomes with too few individuals to look at within-haplogroup coalescents. So here they add more individuals. It is still a small number (425 total) and so I expect that we will see better ones in the next few years.

    The results are nonetheless useful because they provide some nice matches for the archaeology of early agriculture. For example, in Africa:

    We find two periods of population expansion within our sample of lineages originating during the Holocene in western Africa. Although the majority of coalescent events occur during the Holocene, a number of lineages from this sample also coalesce during the Upper Paleolithic. The earliest growth begins at ≈38,000 ya (CI: 33,500–45,000 ya) (Table 1 and Fig. S1) and the second period begins at ≈4,600 ya (CI: 3,000–10,000 ya) (Table 1 and Fig. 1B). The correspondence between the timing of genetic evidence for a sharp increase in population size at 4,600 ya in our Holocene sample of sub-Saharan Africans and the archaeological evidence for origins of agriculture in western Africa is quite close (Fig. 1B and Table 1). In contrast, our southern African Upper Paleolithic sample representative of hunter-gatherers shows no growth over the past 20,000 y. We suggest Bantu-speaking farmers and other pastoralist groups migrated throughout southern Africa 2,000 ya (27) without impacting southern African mtDNA lineages (Fig. 1B).

    We can't really understand the pattern of genetic variation within Africa without understanding when the population grew. In Africa, Middle Stone Age genetic variation must have been more extensive than that in other regions of the world. But the survival of that MSA variation to the present day depends on the demography of populations over the past 50,000 years. In a growing population, fewer lineages will be lost by random genetic drift. So if Gignoux, Henn and Mountain are right about the growth of West African populations by 35,000 years ago, we might expect that region to preserve some extensive variation from MSA times. That might explain why that population preserves very deep Y chromosome lineages [3]. Regarding only mtDNA, one might conclude that a historical paucity of migration between hunter-gatherer and agricultural groups would be the most important reason why MSA variation remains in the present-day African population. This has been the explanation for survival of deep mtDNA lineages in southern Africa, for example. The Y chromosome result and the current paper remind us that population growth can also preserve variation from earlier time periods.

    I think this proposal of African population history matches very well the model that we assumed in our acceleration paper [4], which we based on the archaeological record. We suggested early population growth in Africa by 35,000 years ago followed by an agricultural expansion after 5000 years ago. The evidence for relatively late agricultural intensification, within the last 4000-5000 years in sub-Saharan Africa, is very clear archaeologically. Less clear: How big was the earlier, pre-agricultural human population? The LSA might correspond to a demographic intensification, generally after 45,000 years ago. Genetics has certainly seemed to support such a view, and we found it consistent with the evidence that positive selection had increased in rate much earlier in Africa than in other regions. Still, the more detailed study by Gignoux and colleagues helps to clarify this picture.

    The results also show agricultural population growth to have been late in Southeast Asia.

    Direct archaeological evidence for rice agriculture in southeastern Asia dates to only ≈4,400 ya in Thailand (28). Agriculture spread throughout Island Southeast Asia, with evidence of rice in Taiwan again dating to ≈4,400 ya. Our Southeastern Asian Holocene population size curve indicates expansion beginning ≈4,700 ya (CI: 3,000–5,700 ya) (Fig. 1C and Table 1).

    Again, useful. I think we need to exert some effort making sure that the initial dispersal of people into South/Southeast Asia can be differentiated from the post-agricultural history. But assuming that Gignoux and colleagues are correct, it makes sense in an overall picture of slowly adapting early crops to tropical climate regimes, or replacing early domesticates with different ones in those areas.

    I am less sanguine about their results for Europe. They show a gradual period of growth associated in time with the Younger Dryas (around 12,000 years ago), which could make sense in the archaeology. But I am not convinced that the "European" haplogroups here are really European to that time depth. We know that the Neolithic and post-Neolithic saw some large-scale shifts in the frequencies of mtDNA haplogroups in Central and Western Europe. Some Upper Paleolithic Europeans probably contributed mtDNA to this later population, but I have no confidence that the proportion was great enough to accurately infer the demography of that pre-Neolithic population. (This is also a problem with the current paper in Current Anthropology by Peter Rowley-Conwy. I'll discuss this sometime soon.)

    The next frontier in reconstructing the population history of Europe will be ancient DNA. A good sample of Neolithic and pre-Neolithic whole mtDNA genomes would settle this question and allow inferences about the kind of demographic recovery Europe underwent after the Last Glacial Maximum.

    An open question is to what extent the other populations have similar problems. The European population of today reflects West Asian population dynamics 10,000 years ago. The East African population today reflects West African population dynamics from before the Bantu expansion, possibly to a similar extent. The population of Southeast Asia reflects the population dynamics of early rice agriculturalists in South China. And so on.

    Adding large-scale migration and partial population replacement to this kind of demographic analysis is not easy, but it will be essential if we want a better picture of how agriculture affected human populations. Considering these problems, I think it's easy to see why I started working on Holocene population dynamics. Evidence about Late Pleistocene populations, like MSA Africans and Neandertals, still lies within our genomes. But we see it through a lens. Holocene population dynamics -- movements and population growth -- distort that lens. If we don't account for those Holocene dynamics, we will conclude wrongly about the earlier dynamics.

    I like this a lot, because this is what anthropology is really good for. We can bring a lot of archaeological and historical knowledge to bear on the question of post-agricultural population dynamics. But it's a deep, deep field with a lot of specialized literature.

    References

    1. Henn BM, Gignoux CR, Jobin M, Granka JM, Macpherson JM, Kidd JM, Rodr\'ıguez-Botigué L, Ramachandran S, Hon L, Brisbin A, et al. 2011. Hunter-gatherer genomic diversity suggests a southern African origin for modern humans. Proceedings of the National Academy of Sciences [Internet] 108:5154–5162. Available from: http://dx.doi.org/10.1073/pnas.1017511108
    2. Gignoux CR, Henn BM, and Mountain JL. 2011. Rapid, global demographic expansions after the origins of agriculture. Proceedings of the National Academy of Sciences [Internet] 108:6044–6049. Available from: http://dx.doi.org/10.1073/pnas.0914274108
    3. Cruciani F, Trombetta B, Massaia A, Destro-Bisol G, Sellitto D, and Scozzari R. 2011. A Revised Root for the Human Y Chromosomal Phylogenetic Tree: The Origin of Patrilineal Diversity in Africa. American journal of human genetics [Internet]. Available from: http://dx.doi.org/10.1016/j.ajhg.2011.05.002
    4. Hawks J, Wang ET, Cochran G, Harpending HC, and Moyzis RK. 2007. Recent acceleration of human adaptive evolution. Proceedings of the National Academy of Sciences, U. S. A. [Internet] 104:20753–20758. Available from: http://dx.doi.org/10.1073/pnas.0707650104
    Tags: 
    mtDNA migrations
    population growth
    agriculture
    demography
    mtDNA
    Neolithic
    Africa
    population structure
    Asia
    Europe
    Synopsis: 
    A study of mtDNA variation attempts to find the times and magnitudes of population expansions in early agriculturalists.

  • Mailbag: Migration and Malthusianism

    Sat, 2010-04-03 13:13 -- John Hawks

    Re: "Misinformation about brain evolution"

    Love your blog!. So many science blogs are tied down with science vs religion. I want more science!

    I would think another way to avoid Malthusian crises is migration. The idea of a better life over the next ridge is a major human compulsion. Certainly hasn't stopped in today's world despite major attempts to limit it. Of course, brilliant graduate students are welcome but poor peasants are not.

    Thanks so much for the kind words!

    True enough, although migration is only a temporary out. My own thinking is that these ancient populations were locked in a source-sink dynamic. Some places were good to live, at least for most of the time, and produced excess people who migrated elsewhere. But the rest of the human range was not-so-good to live, and people there were constantly reproducing below replacement. So they absorbed migrants who were, in the long-term sense, doomed.

    So in that sense, I think migration is the most important way to deal with density-dependence for these ancient people. But from the genetic point of view, it may not have really been better than staying and fighting it out -- except that might have degraded the local ecology in a way that turned a relative source into a sink!

    Tags: 
    brain
    population growth
    paleoclimate
    source-sink dynamics
    migration

  • Misinformation about brain evolution

    Mon, 2010-03-29 10:58 -- John Hawks

    Due to Jerry Coyne, I encountered an interview in the Guardian with Colin Blakemore: "Colin Blakemore: How the human brain got bigger by accident and not through evolution."

    The headline is a misnomer, as Blakemore is not denying evolution, he is denying selection. But Blakemore's argument is based completely on a false presentation of the facts. Consider:

    The question is: why is it so big compared to the brains of our predecessors, such as Homo erectus? Until 200,000 years ago, there had been a gradual increase in brain size among hominins, starting three million years ago. Then, abruptly, there was a remarkable increase of about 30% or so.

    That's Blakemore. Now, here's a chart of endocranial volumes of Pleistocene human fossils:

    Endocranial volumes of Pleistocene human fossils

    Endocranial volume against time for fossil Homo.

    Time is in thousands of years before present, running left to right.

    As you can see, there's no sudden jump 200,000 years ago, or at any other time. The data, such as they are, are consistent with a single pattern of increase over time, as pointed out by Sang-Hee Lee and Milford Wolpoff (2003).

    Heck, it's the lack of a sudden jump that has gotten all the attention. Because if "modern" humans suddenly showed up in Africa 200,000 years ago, and all of a sudden had vastly larger brains than any other hominins, wouldn't that be a simple and tidy story? Don't you think we'd all be talking about the sudden origin of modern humans as reflected by their larger brains?

    It just didn't happen.

    Well, it's one thing to be empirically wrong. That's a simple error that's easily corrected. But Blakemore, relying on the erroneous assumption of a single shift in brain size, asserts that neutral macromutations must be an important mode of human brain evolution:

    Genetic studies suggest every living human can be traced back to a single woman called "Mitochondrial Eve" who lived about 200,000 years ago. My suggestion is that the sudden expansion of the brain 200,000 years ago was a dramatic spontaneous mutation in the brain of Mitochondrial Eve or a relative which then spread through the species. A change in a single gene would have been enough.

    I hope that the empirical pattern is enough to convince you that this hypothesis is false. The "sudden increase" simply did not happen.

    But in case you need more persuasion: Blakemore here assumes that the increase in brain size had no negative consequences. Otherwise it couldn't proceed neutrally. Here is his argument:

    The environment of early humans was so clement and rich in resources that this greedy new brain, which would have absorbed even more of the body's energy, could be sustained without danger. Later, when times got hard, during droughts or climate changes, it helped us deal with these crises, which could otherwise have killed us off, by dreaming up novel ideas to problems.

    You see the outline: Life was easy, and humans could grow fat-brained, like so many sheep. Fortunately, our fat brains were then useful when times were tough. Blakemore describes this as somehow different from the idea that brains were adaptive -- it's in fact just another adaptive story for larger brains.

    But it falls apart, when we consider that assumption -- life was easy. I put it to my students this way: Suppose you lay a lot of sugar beets out on your land. What will happen to the deer population?

    The answer is not that the deer will grow fat-brained and later evolve to conquer humanity. The answer is that there will be a lot more deer.

    Population growth is much faster than adaptation, and it's hundreds of times faster than a neutral gene can transit through the population. Humans in the past were not a static population, living in peace with an abundant environment. They were repeated faced with Malthusian crises -- on submillennial timescales. That's why a close understanding of climate variability is so relevant to our evolution. The fact that tools and behaviors change so slowly in the Middle Pleistocene is informative -- it shows that humans weren't coming up with dramatically new ways to track shifting ecologies.

    And that means that the selection pressures of the energetic and life history constraints on the brain were repeatedly imposed on human populations. A substantial increase in brain size should have immediately been disadvantageous -- if it had no compensatory benefits to fitness.

    What remains is testing the hypotheses about those benefits to fitness. Blakemore actually is presenting one such hypothesis -- that a larger brain mostly was adaptive because of its ability to transmit traditions. That's testable, and is consistent with the greater transfer of information apparent in recent archaeological traditions compared to Middle Pleistocene ones. But there are other hypotheses as well, and it is quite difficult to compare them with the available record.

    That's why it's so important to state the empirical record accurately.

    UPDATE (2010-03-29): A reader points out that Malthusian crises, in terms of resource or food availability, may have been avoided by warfare or predation -- people kill each other instead of starving. I see that point, particularly where we consider the way that epidemic disease can relax competition for food until population growth resumes. Performing well under predation or competition would be one way that brain size might have had compensatory benefits to fitness beyond its energetic and life history costs.

    References:

    Lee S-H, Wolpoff MH. 2003. The pattern of evolution in Pleistocene human brain size. Paleobiology 29:186-196.

    Tags: 
    paleoclimate
    demography
    MSA
    population growth
    brain
    Middle Pleistocene

  • SNPtastic India

    Wed, 2009-09-23 14:49 -- John Hawks

    The cover story in Nature this week is a paper about the population history of India, from David Reich's lab. It's an important contribution to our knowledge of human genetic variation, and provides a very interesting set of data for further investigation of modern human origins, the dispersal of agriculture into the subcontinent, and the history of more recent Indian populations.

    Here's the abstract:

    India has been underrepresented in genome-wide surveys of human variation. We analyse 25 diverse groups in India to provide strong evidence for two ancient populations, genetically divergent, that are ancestral to most Indians today. One, the 'Ancestral North Indians' (ANI), is genetically close to Middle Easterners, Central Asians, and Europeans, whereas the other, the 'Ancestral South Indians' (ASI), is as distinct from ANI and East Asians as they are from each other. By introducing methods that can estimate ancestry without accurate ancestral populations, we show that ANI ancestry ranges from 39–71% in most Indian groups, and is higher in traditionally upper caste and Indo-European speakers. Groups with only ASI ancestry may no longer exist in mainland India. However, the indigenous Andaman Islanders are unique in being ASI-related groups without ANI ancestry. Allele frequency differences between groups in India are larger than in Europe, reflecting strong founder effects whose signatures have been maintained for thousands of years owing to endogamy. We therefore predict that there will be an excess of recessive diseases in India, which should be possible to screen and map genetically.

    The number of individuals is not huge for the purposes of population genetic analysis -- only 132 people from 25 groups -- but it is very significant in terms of recent samples. By comparison, it is around double the number of effective individuals in any of the HapMap v.1 populations, genotyped at more than 560,000 SNPs.

    The results of the study are basic population genetic issues, including the degree of endogamy, the pattern of regional differentiation, the likelihood of discovering new recessive genetic disorders by additional sampling. Some notes:

    Population mixture. The authors propose that today's groups descend in varying proportions from two ancient (and no longer existing) populations, which they call "ancestral North Indian" and "ancestral South Indian".

    I'm always skeptical of mixture models, especially when the putative source populations no longer exist. There are just too many ways that structured migration or dispersal can lead to the appearance of mixture. People once thought of "Alpines" as a mixture of pure Nordic and Mediterranean elements, after all-- and that was just because their heads were mesocephalic.

    Still, with a half-million SNPs, it's possible to do a better job testing the hypothesis of mixture versus structured migration. The authors in this paper didn't -- they applied a simplified "3 Population Test" that compares the empirical allele frequencies to proportions expected under only two scenarios: simple mixture or complete isolation. It seems to me that the null should be simple isolation by distance, which would give the same result as "mixture" according to their test. If you really want to look for population mixture, you need to involve the dimension of time, for example, by demonstrating the antiquity of haplotypes that have mixed together.

    So I don't accept this ancestral division, certainly not at face value. It does seem plausible that West Asian (and thereby European-related) genes have introgressed into India over time, perhaps in association with the growth of high-density agricultural populations. Maybe some of this gene flow occurred under the influence of positive selection, but processes of elite dominance and differential growth may have been sufficient.

    Regional differences. The results show a greater degree of regional genetic differentiation in India than has been found for continental Europe. Still, with an FST of only 0.01, we're not talking about major population splits here. With that number, the subcontinent is closer to panmixia than one might expect for a region its size. The authors suggest that founder effects explain the regional differentiation:

    We propose that the high FST among Indian groups could be explained if many groups were founded by a few individuals, followed by limited gene flow. This hypothesis predicts that within groups, pairs of individuals will tend to have substantial stretches of the genome in which they share at least one allele at each SNP. We find signals of excess allele sharing in many groups (Supplementary Fig. 2), which as expected tend to occur in the groups that have the highest FST values from all others (P = 0.002 for a correlation). To estimate the age of founder events, we measured the genetic distance scale over which allele-sharing decays, and verified the robustness of our procedure by simulation (Supplementary Fig. 3). Six Indo-European- and Dravidian-speaking groups have evidence of founder events dating to more than 30 generations ago (Supplementary Fig. 2), including the Vysya at more than 100 generations ago (Fig. 2). Strong endogamy must have applied since then (average gene flow less than 1 in 30 per generation) to prevent the genetic signatures of founder events from being erased by gene flow.

    I don't think that explanation works. With those times in generations, we're talking about events within the last 600-2000 years. Since all these calculations are done on the whole dataset assuming complete neutrality, I think we should look more closely at the distribution of LD across loci. It seems likely that some of the high-LD loci that appear to point to founder effects will actually be found to be selected.

    Relationships of Indian to non-Indian populations. One of the real problems of assuming a tree with no migration is that it leads to statements like this:

    [T]he ANI [ancestral North Indian] and CEU [HapMap European sample] form a clade, and further analysis shows that the Adygei, a Caucasian group, are an outgroup (Supplementary Note 4). Many Indian and European groups speak Indo-European languages, whereas the Adygei speak a Northwest Caucasian language. It is tempting to assume that the population ancestral to ANI and CEU spoke 'Proto-Indo-European', which has been reconstructed as ancestral to both Sanskrit and European languages, although we cannot be certain without a date for ANI–ASI mixture.

    Some of the common ancestors of some living Europeans and some Indians were probably speakers of proto-Indo-European speakers. But we can easily refute the hypothesis that all of the common ancestors did so -- some of those common ancestors lived more than 40,000 years ago, as is well-known from the mtDNA chronology. The tree model with complete isolation does not explain the data. So as simple as it is -- and as well-used by Cavalli-Sforza and others -- it would be better to use a more accurate model.

    UPDATE (2009-09-24): Gene Expression has a full review of the paper.

    UPDATE (2009-09-27): Very interesting angle by Suvrat Kher at Reporting on a Revolution:

    The Indian Press has made a hash of the finding....

    But I can't blame the press entirely. The scientists who gave interviews to the press didn't mention this. They wimped out on reporting this potential inflammatory and politically incorrect finding. This is just poor and irresponsible science outreach on part of the scientists. How can you ignore a finding that is staring out at you from the very paper you are talking about? The press may be guilty of not digging in but it was just reporting what the scientists told them.

    References:

    Reich D, Thangaraj K, Patterson N, Price AL, Singh L. 2009. Reconstructing Indian population history. Nature 461:489-494. doi:10.1038/nature08365

    Tags: 
    India
    population history
    admixture
    HapMap
    population growth
    genomics

  • Ceci n'est pas un pothole

    Thu, 2009-03-26 10:54 -- John Hawks

    In 2005 I wrote this:

    "Unusual compared to the rest of the genome" is a phrase you should expect to hear a lot of in the next few years.

    I was looking back at that old post today, as I'm writing new stuff about bottlenecks. It's about the ability to detect selection using the HapMap data -- written just as I was starting to think about recent selection:

    Suppose we wanted to use a detailed topographic survey of a road to find the potholes. But for everyday roads, there is a problem -- there are lots of bumps and grooves that aren't potholes. And different parts of the road are more or less bumpy. It would help a lot if we could use the empirical distribution of bumps to simulate a section of road -- then we could figure out whether anomalies in the real road were likely to be potholes or not.

    Now suppose that the road isn't just pocked with the occasional pothole -- it has a pothole every three or four feet. Remember why we're using simulations -- not only do we not know where the potholes are, we don't know how common they are. So our simulations based on the pothole-rich road will find that pothole-sized bumps are normal. If pothole-sized bumps are not unusual, then our simulation can have only one result: a pothole is not a pothole.

    So I've been writing about the same problem for over three years -- the problem of ignoring history and archaeology when applying models of population history, and how they skew simulations of genetic drift. Time to do something about it, I guess.

    Tags: 
    population growth
    recent selection
    HapMap
    population history

  • The ancient struggle for existence between humans and giant clams

    Fri, 2008-08-29 12:53 -- John Hawks

    Giant clams are in the news today, helping to drive the expansion of modern humans out of Africa. Can we believe it?

    • The paper (Richter et al., 2008) describes a new species of giant clam, distinct from others in reproductive cycle, habitat preference and size.
    • This new species is mainly found in shallow water reefs.
    • Today, the species makes up a very small proportion of the total Red Sea giant clam count.
    • Before the last interglacial, this species made up as much as 80 percent of the giant clam count, as assessed by shells from reef terraces. This proportion decreased around the last interglacial, and again in historic times.

    This sounds like the classic megafaunal exploitation story, as it is being reported. Shells become an important debris of humans in Northeastern Africa by 125,000 years ago (Walter et al., 2000), and were important elements of the MSA along the coasts of North and South Africa (McBrearty and Brooks, 2000). So it would not be surprising if these people recovered giant clams, particularly if those clams were readily available in shallow water. Giant clams are similar to large tortoises in terms of their recovery and exploitation, and there is already good evidence that tortoise size decreased with overhunting as Late Pleistocene human populations grew. By the Upper Paleolithic, people in some parts of the Mediterranean began to harvest small shellfish to an extent that put pressure on their populations. The giant clams would be an early example of the same phenomenon, made more precarious by the shallow-water habits of this particular clam species.

    Since refuting the Neandertal inferiority complex is a theme this week, I should point out that Neandertals who lived on the coast also exploited shellfish, an observation that I discussed here. The exploitation of coastal resources is not specifically“modern”. Coastal populations of terrestrial predators typically eat marine species, for example, coastal brown bears in Alaska systematically harvest soft-shelled and razor clams (Smith and Partridge, 2004).

    So the clams shouldn’t be surprising. Are they interesting? I think it is another piece of evidence that human populations in Africa during the last interglacial were already large and growing. Archaeological sites from the African Late Pleistocene have been proliferating during the last few decades, but are still underrepresented compared to the density of sites in other regions, especially Europe and the Near East. So you might not get the idea from archaeological sites that the African population was especially large. Yet, across the MSA, we see increasing breadth of faunal exploitation and some systematic recovery of small resources such as shellfish and tortoises. We also see a greater intensity of raw material exploitation and movement, and

    Most important, we now have clear genetic evidence for a large and diverse African population during the Late Pleistocene. That includes the mtDNA genealogy, which now supports the interpretation of an effective population size that had perhaps doubled or more by the last interglacial (I discussed that research here). Put that together with the evidence for structure within this ancient population — either regional differentiation or ecological adaptation — and we have some very interesting demographic knowledge about Africa 100,000 years ago.

    References


       McBrearty S, Brooks AS. 2000. The revolution that wasn’t: a new interpretation of the origin of modern human behavior. J Hum Evol 39:453–563.

       Richter C, Roa-Quiaoit H, Jantzen C, Al-Zibdah M, Kochzius M. 2008. Collapse of a new living species of giant clam in the Red Sea. Curr Biol 18:1–6. doi:10.1016/j.cub.2008.07.060.

       Smith TS, Partridge ST. 2004. Dynamics of intertidal foraging by coastal brown bears in southwestern Alaska. Journal of Wildlife Management 68:233–240. 0.CO;2]doi:10.2193/0022-541X(2004)068[0233:DOIFBC]2.0.CO;2.

       Walter RC, et al. 2000. Early human occupation of the Red Sea coast of Eritrea during the last interglacial. Nature 405:65–69.

    Tags: 
    early modern
    marine resources
    diet
    Late Pleistocene
    population growth
    Africa
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Neandertals

For years, I've worked on their bones. Now I'm working on their genes. Read more about the science studying these ancient people.

Denisova

From a finger bone of an ancient human came the record of a completely unexpected population. My lab is working on the science of the Denisova genome.

Acceleration

The advent of agriculture caused natural selection to speed up greatly in humans. We're uncovering some of the ways that populations have rapidly changed during the last 10,000 years.

Malapa

Just outside Johannesburg, the Malapa site is producing some of the most exciting finds in human evolution. This site is the headquarters of the Malapa Soft Tissue Project.