Who We Are and How We Got Here: Ancient DNA and the New Science of the Human Pastby Published 27 Mar 2018
|Who We Are and How We Got Here: Ancient DNA and the New Science of the Human Past.pdf|
A groundbreaking book about how technological advances in genomics and the extraction of ancient DNA have profoundly changed our understanding of human prehistory while resolving many long-standing controversies.
Massive technological innovations now allow scientists to extract and analyze ancient DNA as never before, and it has become clear--in part from David Reich's own contributions to the field--that genomics is as important a means of understanding the human past as archeology, linguistics, and the written word. Now, in The New Science of the Human Past, Reich describes with unprecedented clarity just how the human genome provides not only all the information that a fertilized human egg needs to develop but also contains within it the history of our species. He delineates how the Genomic Revolution and ancient DNA are transforming our understanding of our own lineage as modern humans; how genomics deconstructs the idea that there are no biologically meaningful differences among human populations (though without adherence to pernicious racist hierarchies); and how DNA studies reveal the deep history of human inequality--among different populations, between the sexes, and among individuals within a population.
"Who We Are and How We Got Here: Ancient DNA and the New Science of the Human Past" Reviews
This book offers readers a description about the human past that has been made possible by recent technological advances in genome research. By comparing whole genomes' worth of DNA from ancient humans of various degrees of antiquity together with the data analysis power of modern computers, a picture of ancient human history has emerged that is filled with multiple migrations by varied branches of the human ancestral family.
The picture that is emerging consists of so many past migrations and mixtures of past populations that it's difficult to know how to give a sense of its complexity in this review. This is compounded by the author's statement that there's an avalanche of new genome data pouring into the field faster than if can be assimilated. The author predicts that the complexity of past human history will become increasingly developed in detail and complexity. The following items highlighted by this review are simply those portions that impressed me as being particularly interesting.
Variation in Human Forms
The variation in human forms varied much more widely 50,000 years ago than it does today. There were at that time alive on earth four major forms of humans. In addition to modern humans there were Neanderthal, Denisovan and Homo-floresiensis (a.k.a Hobbits). The Homo-floresiensis were isolated on the Island of Flores, Indonesia and may have been descendants of Homo-erectus and did not mix with modern humans. However, there was intermixing of Neanderthals and Denisovans with modern humans as late as 50,000± years ago. Almost all non-Sub-Saharan Africans alive today carry traces of this ancestry in their DNA.
DNA Consequences of American Slavery
The contribution of European American men to the average genetic makeup of present-day African Americans is about four times higher than that of European American women (38 percent versus 10 percent). This difference is determined by comparing the differences between Y-chromosone and mitochondrial DNA. This "sex bias" in some human ancestries is evidence of an imbalance in social power between human classes during past history. A similar difference is found in south Asian DNA which is indicative of a past migration or invasion from the Eurasian Steppes. It's interesting how past human sexual behavior, sometimes many years in the past, can be determined by this sort of analysis. [spoilers removed]
Native Americans Closer to Europeans than Asians
Native Americans are more closely related to Europeans than to East Asians. How can this be if the ancestral native Americans came to North America via the Bering Strait crossing which is in northeast Asia? The answer lies in the past existence of a "ghost population" of "ancient north Eurasians" that contributed to the genome or both northern Europeans and Native Americans, but not present-day Han Chinese.
The term "ghost population" is used to describe a population that can be inferred to have existed in the past using statistical reconstruction but that no longer exists in unmixed form. And indeed the bones found in a south-central Siberian grave dating from around 24,000 years ago match the predicted genome of "ancient north Eurasians." The following graphic illustrates the "four population ancestral analysis" that illustrates how the existence of "ancient north Eurasians" was determined.
Sardinians Are Remnant of Early Europeans
It's interesting to note from the above illustration that today's Sardinians are the closest relatives to ancestral Europeans because the mixing with north Eurasians didn't reach them.
Neanderthal Markers in European and Asian DNA
Also of interest from the above illustration is the fact that modern human/Neanderthal mixing occurred with the "ancestral non-Africans" but not with the "predicted ghost population" of ancient north Eurasia. Consequently, present day Han Chinese have a higher percentage of Neanderthal markers in their DNA than present day northern Europeans (4% vs. 2%). This is counter intuitive since the mixing between modern humans and Neanderthal occurred in Europe and the Middle East.
The book contains a chapter which discusses some of the controversies caused by the recent advances in genome research. One subject discussed is the refusal of some Native American tribes to allow bones of their ancestors be analyzed. This has developed from a long history of scientists who have shown disrespect to this ethnic group. The author sees this as an unfortunate situation which he hopes can be resolved with time and improved trust between the two sides.
Problems with Racists
Another issue discussed is the problem with those who object to any analysis of differences between human groups because it gives fuel to racists. The author believes that enforcement of artificial political correctness on genome research would allow those of a paranoid disposition to claim that the scientfic community is hiding the "truth." He says it is best to have an open an transparent discussion of genome differences between racial groups.
NYT Article of Interest
The following is a link (not from the book) to an article about an archeological excavation of a grave of a human who was a mixture of Neanderthal and Denisovan, but not modern human.
Excerpt from Another Book
The following is not from this book. It's a link to an excerpt from Evolving Ourselves by Juan Enriquez and Steve Gullans. I found of particular interest the quote, "There are almost no examples of Neanderthal cavities. Paleolithic and Mesolithic human skulls are almost devoid of cavities." https://t.co/HfAjYUwDoh
This was the book that I wanted the last book I read on the topic to be. Concentrates on the science, lucidly written, although probably best not read when one is too fatigued or sleepy. Its explanations seem as simple as possible but no simpler, which I appreciate. This is a round-up of the most recent (as of about the end of 2017) science of ancient DNA by one of the scientists working on the subject. It's such a fast-moving field right now (faster than print publishing, to be sure) even a year will make a difference, and as a sort of science camp-follower, I look forward to trying to keep up.
I found the work reported on India and Asia to be especially interesting, as it was new to me. (I'd already read Paabo's book on the Neanderthal work, also highly recommended. https://www.goodreads.com/book/show/1... )
Highly recommended, although read it soon, rather like eating your ice cream before it melts.
We geneticists may be the barbarians coming late to the study of the human past, but it is always a bad idea to ignore barbarians. We have access to a type of data that no one has had before, and we are wielding these data to address previously unapproachable questions about who ancient peoples were.. This book has many very, very good qualities. It is, without doubt, the best modern summary of ancient genome research and how it is transforming our understanding of the past available. However, it also carries some very deep, and dangerous, flaws. Reich is so keen to move us forward with new techniques that he tramples past cultural, sociological and anthropological scholarship that helps us to understand how we create narratives and guard against bias. In doing so, his book reinforces destructive ideas about race; human cognition and psychology and class and power. Perhaps ironically, in seeking to free us from antiquated scholarship, Reich plays straight back into dominant narratives that have explained - and justified - racial inequality for centuries.
In many ways these are small flaws, affecting a few chapters at the end. But Reich has created a narrative around this in which he is a hero taking on the idiocy of political correctness, which makes it impossible not to treat this discussion as the center of the book. And as Reich says above, these newcomers to the field of human origins wield enormous influence, which brings with it responsibility for rounded scholarship.
It has taken me a month to write this damn review (long time to have a tab open!) in part because Reich sets us such a trap for the critic: he consistently argues that those critiquing his view of race are motivated by trying to shut the discussion down. People like me are anti-evidence, and unless you are going to argue with him over the sequencing techniques, then the criticism is irrelevant. As it happens, I agree strongly, as do very many who think he is wrong, with the need to have evidence-based discussion about race, gender, intellect, cognition and human origins. Especially given the rise of overt racism, and the flock of racist men to blogs and discussion forums around genetic prehistory. So it has been important to me to ensure that it is clear that my objections are not to having a conversation, they are to his conclusions, and the way he has framed the debate, and most of all, what he overlooks.
Now, Reich argues that he is countering racism: his book strips back the stupid claim that 'races' have existed for any significant fraction of human existence, and gives huge weight - as does all modern genetic work - to understanding that our ancestors mingled, migrated and procreated much more expansively than we had previously assumed. Our modern 'populations' have existed for not much more than 5000 years in most cases. (This itself shows what we mean - many populations actually have been relatively distinct for longer than that, the San, Australia's Aboriginal groups, Native Americans - but they don't correspond to our race ideas, which lump all Africans together, all Oceanic groups together etc - really, it is the inhabitants of Eurasia who have mingled incessantly, creating the populations who tend to hold social, economic and political power in our current world) Multiculturalism has been a consistent feature of human societies, and yes, conflict is as much a part of that condition as harmony: this is part of who we are, in all our glorious complexity. But the fact that Reich doesn't think he is making racist assumptions doesn't change two big errors: his argument that cognitive differences could exist between "large population groups" (i.e.: races) and his infuriating and frankly petulant dismissal of First Nations concerns around genetic research.
On the first: to start, Reich is not in the majority in thinking that large populations are the most effective way to look at genetic difference - he himself outlines his differences with Svante Paabo in the book, although he talks down the support that remains for Paabo's view that clines is a more enlightening slice. He admirably starts by pointing out that race, as we think we understand, has been largely debunked. He attempts to distinguish himself from the rubbish spouted by journalist Nicholas Wade, and the prejudice of James Watson. But as the book progresses, he focuses increasingly on the possibility of differences which have evolved over the last 5000 years, providing markers between populations - despite the fact he presents no evidence for this. In the end, he seems to be warning that they might be right about some things, attacking his colleagues for using truisms like, there is more genetic variation within population groups than between them (this is, by the way, simply true) instead, presumably, of focusing on those differences which can be found. The fact that there is plenty of scholarship on those differences, such as skin colour, height and susceptibility to disease, doesn't count of course, because really what Reich is getting at is cognitive, personality and the "real" question of intelligence. Who is, after all, the most human? the fact we have little idea in any form of scholarship of what that actually means doesn't slow him down at all. And honestly, it should.
On the IQ: look, there are many great articles on this already on the Interwebz. Start with Kevin Mitchell in the Guardian . The issue here isn't that genetics doesn't predict the possibility of natural selection causing complex differences between populations (the only argument that Reich addresses in the book, and one which he says comes from political correctness, adding insult to disagreement); the issue is that the main narrative of modern society is that these differences do exist, when there is no untainted evidence for it. Mitchell in this link accepts the IQ test as a measure of intelligence - but many, many scientists do not. We have much evidence, in fact, that economic inequality and stereotype threat: much of this research is centered on gender difference in maths . This is why the one main significant study into IQ and genetics - which Reich makes much of - focused on a very uniform genetic population in a country with tiny economic and social inequality, and even then the implications of its results have been widely challenged.
Reich's own research on earlier periods challenges the simple search genetics has for the unlocking nature of consciousness and humanity. He points out that despite large resources, there simply doesn't seem to be evidence that genetic adaptation closely precedes leaps in human development. This is not a surprise to evolutionary biologists, who have known for some time that our capacity to learn and create social structures which then shape our individual cognitive development is our strongest adaptation; that our closest primate relatives have genetic capacity for language and tool use, as well as often superior memory and recall. But the key lesson here: that we have an extreme ability to socially shape our children and hence create ourselves should also result in an understanding that we ourselves, us scientists, are also created and shaped by the societies that created us, is one Reich usually doesn't appreciate the impact of.
In one rather infuriating section he comments that we should take the same approach to race as to gender, throwing out:
Most people accept that the biological differences between males and females are profound, and that they contribute to average differences in size and physical strength as well as in temperament and behavior, even if there are questions about the extent to which particular differences are also influenced by social expectations and upbringing (for example, many of the jobs in industry and the professions that women fill in great numbers today had few women in them a century ago). Today we aspire both to recognize that biological differences exist and to accord everyone the same freedoms and opportunities regardless of them. It is clear from the abiding average inequities that persist between women and men that fulfilling these aspirations is a challenge, and yet it is important to accommodate and even embrace the real differences that exist, while at the same time struggling to get to a better place.This view, that gender inequality is just a bit of thorny issue society is working through, that most people accept that gendered differences in 'temperament' are 'profound' bears little resemblance to any serious scholarship on either gender, or neuroscience (which consistently finds less and less gendered differences), or for that matter the goddamn zeitgeist at the moment, and summarises Reich's dismissiveness.
Reich at times shows flashes of insight into how social and biological factors interact: for example noting that genetic predictors in (again, uniform and highly equal society) educational rates may relate to differences in fertility, not cognition, or his wonderful aside that West Africans might not be faster, but just more genetically diverse than others, but when it hasn't been forcefully brought to his attention by a sociologist he met at a dinner party, he seems unaware that what he regards as common knowledge comes from a worldview based on relationships of power and social roles. In this context, his blithe assumption that we can find cognitive differences between populations - despite the complete lack of agreement into how to measure or understand cognition; and an awareness that our "common sense" assumptions are largely shaped by our social environment - is an infuriating result of isolating hard science from the social sciences and humanities.
Nowhere is this lack of awareness that he has a worldview more evident than in his frustrated complaints about the role of First Nations peoples - particularly in the Americas - in refusing participation in genetic testing. Reich's bewilderment as to why this is even an issue is clear:
Scientists interested in studying genetic variation in Native American populations feel frustrated with this situation. I understand something of the devastation that the coming of Europeans and Africans to the Americas wrought on Native American populations, and its effects are also evident everywhere in the data I and my colleagues analyze. But I am not aware of any cases in which research in molecular biology including genetics—a field that has arisen almost entirely since the end of the Second World War—has caused major harm to historically persecuted groups.and leads on to hints of wanting to disregard agreements with tribal councils not to proselytise around this research:
I wonder if the distrust that has emerged among some Native Americans might be, in the balance, doing Native Americans substantial harm. I wonder whether as a geneticist I have a responsibility to do more than just respect the wishes of those who do not wish to participate in genetic research, but instead should make a respectful but strong case for the value of such research.
Reich's claim that his research field has not done harm is a little naive. For starters, it involves his version of harm, which excludes the exploitation of genetic material for the primary gain of other groups. It assumes that his post-Enlightenment worldview - in which the search for information is noble, and never dangerous, and in which experimentation is more worthy than spiritual contemplation, is more worthy than differing worldviews which view knowledge without protection, context and responsibility as dangerous. It also ignores the attempts to patent genomic material in the 1990s, and the thirst for profit that US biomedicine is embroiled in, rarely to the benefit of participants. He lauds the work of researchers working with Aboriginal groups in Australia, without realising apparently that this work rests upon recognising that work with genetic material of Aboriginal groups must meet needs the community has identified. That is, it is about listening, respecting and offering resources: none of which is evident in Reich's approach to any of this.
So, the good bits? Reich loves the pursuit of knowledge and it shows. And while he struggles so much with not recognising he has biases, he is refreshingly free from attaching his ego to particularly theories. He cheerfully admits where genetic research has proven his assumptions wrong, and this makes most of the book a page-turner, able to draw a reader in to rapidly shifting worlds of difference.
Reich tackles a range of topics here: including the sensitive issue that the genetic evidence indicates we have more female ancestors than male. This process results from bottlenecks, or times where men fathered children on a wide range of women. While Reich clearly fears this will upset modern scholars, it is hardly a surprise to anthropologists well aware that polygynous child rearing is more common than polyandry, and that war and conflict are largely driven male invading forces. His research into the Indian caste system is fascinating, indicating the long-term effectiveness of social separation within an existing community, and providing really interesting takes on the interaction between social structures and genetic ones. The Brahmin caste, he argues, is far from purely different genetic stock, but bears markers of centuries of incestuous procreation and social isolation. I wanted far more on the Southern Route theory, and the role of Austronesian analysis - particularly given a month before the book came out, cave art was dated to 60,000 years in Northern Australia, which, if accurate, comes down solidly in favour of an early Southern route expansion (and Denosovan contact after arrival on the continent - or errors in genetic dating). Reich is well aware that this book is written at a moment in time, and it takes a certain courage to do that, as no doubt many of his current theories will be debunked in coming years. In being that brave, he's given the layperson a fabulous chance to explore a field in flux. It is just such a shame that he chose to mar this with an unsubstantiated argument about possible things people may find into the future, in a way which feeds into racism and sexism.
This was a fantastic condensation of modern research on genomics and it's effect on our understanding of anthropology and history. Really, what is it with biologists that they are able to write these books understandable to a relatively lay audience without hiding entire detail about how the scientists go about doing their research and draw conclusions:
We scientists are conditioned by the system of research funding to justify what we do in terms of practical application to health or technology. But shouldn’t intrinsic curiosity be valued for itself? Shouldn’t fundamental inquiry into who we are be the pinnacle of what we as a species hope to achieve? Isn’t an attribute of an enlightened society that it values intellectual activity that may not have immediate economic or other practical impact? The study of the human past—as of art, music, literature, or cosmology—is vital because it makes us aware of aspects of our common condition that are profoundly important and that we heretofore never imagined.
Not that some details are hidden. Like use of Principal Component Analysis and other statistical techniques and how they get around problems with these techniques is mostly elided. Still it was fun learning about things Four Population Tests to identify likely common ancestors and how they group current and past populations of people.
The weakest parts of the book are when Reich is trying to walk the tight rope of modern connections between race, behavior and genetics. Which is understandable, because it is a difficult topic. But his bad arguments don't do well for the values he wants to espouse. There is a lot of is vs. ought confusion, with no consistency. This is especially egregious in Chapter 11. Why do I need to be reminded of treating individuals as individuals, just because we find something about group averages. There's something to be said about Nietzsche, that he was correct to claim that trying to derive all our values from objective truth is not ideal, to say the least. But an interesting quote:
I have deep sympathy for the concern that genetic discoveries about differences among populations may be misused to justify racism. But it is precisely because of this sympathy that I am worried that people who deny the possibility of substantial biological differences among populations across a range of traits are digging themselves into an indefensible position, one that will not survive the onslaught of science. In the last couple of decades, most population geneticists have sought to avoid contradicting the orthodoxy. When asked about the possibility of biological differences among human populations, we have tended to obfuscate, making mathematical statements in the spirit of Richard Lewontin about the average difference between individuals from within any one population being around six times greater than the average difference between populations. We point out that the mutations that underlie some traits that differ dramatically across populations—the classic example is skin color—are unusual, and that when we look across the genome it is clear that the typical differences in frequencies of mutations across populations are far less. But this carefully worded formulation is deliberately masking the possibility of substantial average differences in biological traits across populations.
Anyway the book is a lot of fun. One of the funniest parts was about them finding proof for West Eurasian ancestry of large parts of South Asian population:
They did not want to be part of a study that suggested a major West Eurasian incursion into India without being absolutely certain as to how the whole-genome data could be reconciled with their mitochondrial DNA findings. They also implied that the suggestion of a migration from West Eurasia would be politically explosive. They did not explicitly say this, but it had obvious overtones of the idea that migration from outside India had a transformative effect on the subcontinent.
So to get around this:
We wrote that the people of India today are the outcome of mixtures between two highly differentiated populations, “Ancestral North Indians” (ANI) and “Ancestral South Indians” (ASI), who before their mixture were as different from each other as Europeans and East Asians are today. The ANI are related to Europeans, central Asians, Near Easterners, and people of the Caucasus, but we made no claim about the location of their homeland or any migrations. The ASI descend from a population not related to any present-day populations outside India. We showed that the ANI and ASI had mixed dramatically in India. The result is that everyone in mainland India today is a mix, albeit in different proportions, of ancestry related to West Eurasians, and ancestry more closely related to diverse East Asian and South Asian populations. No group in India can claim genetic purity.
And for the rest of the chapter, he deadpan goes on using the ANI-ASI terminology.
Finally, no one comes out looking good when you go far back in time. And we are mixes all the way down.
Such fascinating science and research on ancient DNA. I also really loved all the research about the Iranian Nomad populations that are basically the tribe that took over Europe because those are my people (kind of because there was a lot of mixing). It was also stunning to see how inequality and male domination affected genetics. Basically a few really powerful men who spread their DNA far and wide. Women obviously can't have too many children, but also history seems to be just conquering armies of men spreading their seeds over conquered populations of women.
He also talks at the end about race differences and how we should be prepared to deal with what advanced DNA science will have to say about that. I think he's a bit more confident than his data can take him. I think the DNA stuff is obviously clear to him, but he's not an IQ scientist and I think most people who study cognitive testing believe that it is far from being scientifically rigorous or rooted in genetic differences. In other words, we haven't been able to separate genetics from environment when it comes to cognitive ability. Reich may be confident he can parse out modern races from their DNA, but I do worry about trying to plot races on cognitive factors. By all means, we should look at diseases and all sorts of stuff that have clear genetic variants, but before we start talking about intelligence, we better make sure the science on that is air tight.