An excellent review of modern work on ancient DNA and its significance to human history. Most of the work discussed was done in the author's laboratory. The author is clear, but he is the head guy, not a science journalist like Carl Zimmer, and he cannot or will not elaborate on or repeat his explanations. I don't think anybody would expect a detailed explanation of principal component analysis in a work like this, for example, and some concepts like the four population test are greatly enhanced by good diagrams, but when Professor Reich points out a situation where frequent mutations are uncommon and infrequent ones are common, I found simple re-reading to be inadequate. In a final discussion of the significance of the newly discovered features and likely yet to be discovered features of our genomes on the concept of race, the author refreshingly says,
If we aspire to treat all individuals with respect regardless of the extraordinary differences that exist among individuals within a population, it should not be so much more of an effort to accommodate the smaller but still significant average differences across populations. ( )

Really interesting subject matter but way too much detail, facts, figures, dates, etc. Liked the first and last few chapters the best. ( )

This is the least satisfying of the books I've read/listened to about genetics and the history of human evolution.

In many ways it's excellent. Reich is voracious in absorbing and telling us about other people's research as well as his own. His ego isn't tied up in his own theories; he's enthusiastic in reporting on research results that overturn his own theories and prior work. In many ways, it's both informative and enjoyable.

And yet. Reich seems utterly unaware that he has any biases. He says he's arguing against racism, being very clear that our traditional ideas about race just have no basis in science. Then he goes on to say that the best way to study human genetics is by large population groups, and that some large modern population groups have been separated long enough for significant differences of cognition and temperament to exist.

He argues that a good way to test this is by intelligence testing and the rate of completing advanced education. There's no science to support this. On the contrary, there's substantial evidence that socioeconomic background, parental educational attainment, and the cultural biases of admission requirements and intelligence tests, have a large impact on testing outcomes and educational attainment.

Reich also offers in defense of his argument for possible significant cognition and temperament differences between large, modern population groups the "fact" that no one finds it's controversial to say that there are important biological differences between men and women that produce profound differences in temperament and behavior..... This is of course not correct, and science doesn't support the claim. But he makes this claim, and says the same should be true of discussing differences between large population groups, and that resistance to this comes from "political correctness."

Moreover, he actively resents the resistance of aboriginal peoples, especially in the Americas, to genomic research on their genetics, dismissing out of hand the idea that any substantial harm has ever come from it. Well, in the real world where the aboriginal populations get to have their say, this resistance to genomic research comes from having been lied to about what their genetic material would be used for. In at least one case, they found out how their genetic material had really been used by someone reading a published paper and recognizing the Native American group, and telling them about it. I read about that case in one of the other books in my recent pursuit of what genetics has taught us about our history. It's further worth noting that, while resistance to genomic research is strong among Native Americans, when approached respectfully by researchers who are open, make limited requests, and are very clear about what they'll do, they can sometimes get agreement. And when those scientists respect the commitments they've made, they increase the chances of getting agreement the next time. But it takes a long time to rebuild broken trust, and Reich asks if he should really respect the current laws and agreements on doing genetic research on Native American genetic material.

That's not healthy for science or social and political relations.

Overall, an interesting book, but with some serious concerns..

I bought this audiobook. ( )

If you are love the topics of early human history and hominid evolution, then this book is the one for you. Reich is a researcher right in the middle of the tectonic changes occurring in this area.

The book is comprehensive, informative and very readable. He brings the layperson into this field and you come away with such a great perspective of early human history, evolution and culture.

The only reason that I give it four starts instead of five is that it is a little too focused on what Reich's lab is doing. Understandable, but I was hoping for a somewhat more balanced view of all researchers in the area.

I highly recommend this book to people who are interested in these topics and those who want to get an excellent perspective of humankind and how we came to be. ( )

Fascinating treatment of pre-history as revealed by DNA. Emphasises that there are no pure races: every population is from a mixed ancestry.

I really enjoyed this book because it changed my understanding of what is currently known about human prehistory, and also changed my understanding of how genetics and statistics help disentangle questions that seem very hard to approach otherwise.

As a human being of mixed race, living in a society with people from everywhere in the world, I really enjoyed exposure to what we know about the shared history of humanity, 95% (or more) of which happened before we started leaving any written records.

The book goes into a lot of detail about what is currently known about migrations and mixing among distantly related groups of peoples, which as far as they can tell, has happened repeatedly.

After reading this book I often find myself wondering what it would have been like to live in Eurasia 20ky ago, with a quite different distribution of races of people that don't really have an analog today, and whose looks may have been quite different from those we are used to seeing. Some of these groups exist today only as components in the new mixtures that we now consider races. Understanding these events is made possible by the fact that now we can analyze not only modern DNA but also ancient DNA (eg. 20ky old), and not only mitochondrial or Y chromosome DNA, which is more mainstream.

As a graduates student in an unrelated field, I also found the meta-knowledge the author is giving us, describing how his field is changing, the kinds of questions that would be hard to answer prior to these new techniques, and the problems researchers have had to solve to get there, and what people are currently working on and are excited about. The field seems to be moving fast enough that some of the questions raised in several chapters have had advances since the book was written (only a couple of years ago). I also enjoyed the descriptions of some of the principles used to analyze this type of data. ( )

This one was a fascinating read.
David Reich gives us an overview of this scientific field, its current state and research and I just couldn't get enough of it.
What can be done with the study of ancient DNA and all the discoveries that have been made possible by the technology have blown my mind.
I am sorry and was very frustrated to hear about how politics and the history of racial purity arguments can and do interfere with research in the field. I hope this can be dealt with so in the future, a new book can help me and other curious people learn more about the advances in it. ( )

This book contains two stories. One is that of the breathtaking advances using the study of ancient DNA to tease out humanity’s history. Although, as Reich stresses, we are still in the early stages of learning what it can tell us, we can already see that humanity’s development is more complex than anyone imagined. A basic framework has been established that reveals repeated waves of migration; the book describes thirty major mixture events. As Reich tells it, “the mixture of highly differentiated populations is a recurrent process in our history.” Some of the lines that contributed a portion of the mosaic of our DNA no longer exist. Some of these are named (Neanderthal, Denisovan), others are for now only posited based on DNA traces; Reich calls them “ghost” populations. Since the first modern humans spread from Africa 50,000 years ago, there has never been a “pure” population.
Part of this story is the prospect of how much more there is to unravel as increasing remains are discovered in parts of the world comparatively understudied, such as Africa, and added in.
That essential technique—sampling remains—leads, however, to the second story. The raw material underlying the science comes from gathering old bones and grinding up at least part of them. Entire indigenous tribes have opposed this. Clearly, there are ethical questions involved.
Another ethical issue involves the troubled heritage of eugenics, an early application of (rudimentary) genetic science to root out disease and mental disability through good breeding, including forced sterilization. The memory is repugnant. Yet, study of the genome gives us tools to combat the prevalence of hereditary defects in inbred populations. One such is that of Ashkenazi Jews, among whom certain hereditary diseases, such as Tay-Sachs, flourish. In recent decades, young people at orthodox schools in the United States and Israel are screened to see if they carry the recessive mutations that cause this and a handful of other rare diseases. Matchmakers don’t introduce them to others bearing the same gene. In a remarkably short time, the incidence of these diseases has been reduced. There is potential for using this in other populations, such as the rigidly stratified casts of India. What is that other than eugenics?
More hauntingly, it’s not so long since Nazi propaganda of an Aryan master race unleashed horrible suffering. And an alarming number of the disaffected continue to take this up. Ancient DNA studies now posit a wave of “Aryans” who swept from the central Asian steppe westward to Europe roughly five thousand years ago, largely replacing indigenous populations. Simultaneously, they spread southeast to northern India as well, where they established themselves as the upper caste. The spread of this culture, called Yamnaya, was based on harnessing the newly invented wheel. It seems likely that they are responsible for the spread of Indo-European languages; perhaps they even account for the similarities in the polytheistic pantheons of Norse, Hindu, and Greek mythology. How do we assimilate this knowledge without having it misappropriated by white supremacists? Reich emphasizes that such use of this insight would be mistaken since the Yamnaya culture was formed by mixture. “Ideologies that seek a return to a mythical purity are flying in the face of hard science” (p. 121).
Resistance to the results of investigating ancient DNA also comes from the opposite corner. Reich points to a consensus among anthropologists that race is a social concept and has no biological reality. This, he says, has “morphed . . . into an orthodoxy that the biological differences among populations are so modest that they should in practice be ignored” (p. 250). Those holding this view fear that the study of differences tied to ancestry would revert to earlier pseudo-science-based discrimination. Reich shows understanding for these concerns, yet remains convinced that study of the history of the human genome is valuable, not only for the insights it can yield into the prevention and treatment of disease, but as a means of filling in more of ancient human history than archaeology or linguistics could do without the help of genetics. More than this, rather than reintroduce the notion that biological difference means superiority, Reich is confident that the genome revolution can provide “a way to hold in our minds the extraordinary human diversity that exists in our day and has existed in our past” (p. 272). In sum, his hope is that the fruit of research can give all people a better life.
One of the driving forces in studying our ancestry is to get a better idea of our identity, of our place in the world. As the title expresses it, who we are and how we got here. Of course, you and I are much more than our DNA, and the way we respond to these advances in scientific understanding will also tell much about who we are.
Reich makes no secret in his preface that he would rather have used the time needed to write this book to write scientific papers instead (his profession’s currency, he calls them). I’m glad he wrote this vital book instead, bringing us interested laypeople up to date on both stories he recounts. ( )

This is absolutely the book to read if you're interested in genetic history, either your own or humanity's. Reich zooms out tens and hundreds of thousands of years ago, far past most Big History books, discussing how the latest research on recent discoveries of ancient DNA has begun to make sense of the vast movements of peoples in the dim unremembered mists of time from before we have written records. The rapid pace of technological advancement in genetics research, to the point where we can reconstruct detailed models of peoples we know only from scattered bone fragments, is challenging a lot of what we thought we knew about the past (did humans really evolve solely in Africa? how many waves of migration from Asia to the Americas? how recently did modern racial categories form?), and as astonishing as it is to imagine that we can track the migration and reproductive patterns of long-vanished ethnicities and even extinct subspecies like Neanderthals and Denisovans, genetics has advanced to the point where we can even identify "ghost populations" in our modern genomes - long-dead ancestors who have left no trace of language, settlement, or literature, but whose migrations and mixings live on in our DNA. The rapid pace of discovery in this field means many specific conclusions might be in flux, but as Reich shows, the wealth of knowledge unlocked by DNA sequencing means fields like history and anthropology already have plenty to chew on. I haven't found this kind of rigorous, sustained investigation of the deep roots of our ancestry anywhere else. ( )

This is a very important book - from many points of view. Being able to sequence DNA from ancient human remains means being able to know - really know, not just hypothesize - the degree of relatedness of different species of early humans. This new science is able to tell us, for example, that the early modern humans did interbreed with that other branch of homo sapiens, the Neanderthals; thus modern humans owe as much as 4% of their DNA to Neanderthals. We also inherited DNA from another branch of the family, the Denisovans who, until this time, were know only from one thumb bone and a few teeth discovered in a cave in Russia. The Denisovans were closer to the Neanderthals than they were to us, but we are all distantly related. According to the author's analyses of ancient DNA, there was a fourth branch of homo sapiens - a "ghost" population from whom actual physical remains have not yet been discovered - whom he calls "superarchaic" humans.

The true test of a theory or model is whether it can make predictions that can be verified empirically, and the author describes a fascinating example of this. Knowing that the Americas were populated by people migrating from east Asia across the Bering Straits during the last Ice Age, it had been assumed that Native Americans would share more of their DNA with east Asians than with Europeans. In fact, the first analyses showed just the opposite. On the basis of this unexpected result, the author and his colleagues proposed that there had been another "ghost" population living in northern Europe; some of them migrated eastward and eventually into the Americas, while other migrated southward and contributed towards European ancestry. The author called this group who contributed both to European and Native American ancestry "Ancient North Eurasians"; four years later, physical remains from this ghost population were found; DNA extracted from the bones of a boy who had lived in Siberia about 24,000 years ago showed that Native Americans got as much as a third of their genetic inheritance from Ancient North Europeans.

Analysis of the DNA of different groups of modern humans - and comparison with that of ancient DNA - also shows that the modern "races" - Caucasian, African, South Asian, East Asian, etc - are a very modern "invention". They do not correspond at all - as some would believe - with different groups of ancient homo who, following their migration out of Africa, each followed its own path of evolutionary development. All modern groups of humans are a genetic mixture of different human populations who interbred in the relatively recent past, say up to 10,000 years ago. Continual migration and interbreeding between resident populations and new arrivals is what has created the pallet of human types we know today. The differences we see today concentrated in specific population groups - such as skin color or eyes with epicanthic folds - are relatively modern evolutionary changes.

It is an anti-racist mantra that the average genetic difference between modern population groups is less than differences within these groups. While this is welcome news for anyone who instinctively rejects the idea of there being hereditary genetic differences between different population groups, it does not actually mean that. Contrary to the orthodoxy of many evolutionary theorists, evolution has been ongoing among humans much more recently than the preferred "cut-off" of 50,000 years ago. For groups of people who settled in tropical latitudes, genetic mutations that produced a dark pigmentation of the skin, protecting it from the strong sun, clearly conferred a greater fitness, and hence was likely to spread and become dominant in those populations. For groups of people who domesticated cattle and other animals for meat, a mutation that stopped the gene that permits the metabolism of milk from "switching off" after infancy, thus allowing people to benefit from an important additional source of nutrition from their animals, was also clearly beneficial. There are some whole population groups who still have the original version of this gene that makes them lactose intolerant after a certain age. Rather than leaving information about recent human evolution to leak out via the blogosphere, where it is often used to promote racist theories, the author argues strongly for the scientific community to abandon an untenable orthodoxy and "come clean" about it. This will enable an informed and authoritative narrative about genetic differences between different groups. Differences that originated in response to specific environmental pressures on ancestral populations are just that - differences, without any racist implications of superiority.

On the whole, this is an accessible book for the layman, although some of the technical descriptions about gene sequencing were above my pay-grade. The conclusions were very clear to me, if not always the steps along the way. I also found that I needed to re-read a number of sections two or three times in order imprint their import. It was very worth the effort. ( )

A general overview of the study of ancient DNA as a way to see how peoples and ideas have moved around the world. I did learn a few things I was not aware of (Denisovans, want to know more!) but in general it's using too many words to say not very much.

He touches on the sensitivity of the topic since many religions or extremists or even nationalists have the impression that they are in some abstract way "pure". All information that somehow contradicts this becomes challenged and triggers political debates.

Just some examples:

Peoples in the north of India and peoples in the south of India have strong ideas about their origin and when DNA analysis showed similarities with other peoples, the researchers had to use code names do not upset too many people.

The US and other American countries have a history of attempted genocide against the natives living there. This has resulted in the few fragments remaining guarding their ancient culture fiercely and they do not welcome any outsiders telling them things about their past.

A few other tidbits:

Examining female DNA history and male DNA history leads to different mixes. For instance male mongoloid DNA from the time of Genghis Khan. No female DNA there. Fill in the dotted line yourself.

Africa has mostly been ignored despite having as large diversity as the rest of the world. Maybe because they have been poor and people prefer studying their own DNA rather than someone else's.

( )

This book is by a professional researcher in human genetics, sort of a computational anthropologist. Lots of science and math in it, and a little beyond my understanding of basic genetics.

It is obvious that genetic research has brought about a complete revolution in the medical world in recent decades. But it is sometimes overlooked that genetics has also turned the historical world upside down. This mainly concerns the research of ancient fossils, of humans, animals and plants. Shortly before 2010 it became possible to extract to a limited extent DNA from those fossils and to read out their genome sequences and compare them with others. By examining both the number and the specific place of mutations within that ancient DNA, it is possible to identify lines of kinship or divergence, and thus get a better picture of the populations of millennia ago and their movement across our planet. A well-known example is the presence of a striking portion of Neanderthal DNA in the present inhabitants of Europe and Asia, or the discovery of another extinct human species, the Denisova, of which hereditary traces can be found, especially in Southeast Asia and Oceania.
David Reich portrays this clearly and in great detail, and with authority. He is one of the pioneers in this field. With his own laboratory in Cambridge, Ma., he is at the forefront of this fast-growing field of the Ancient DNA revolution. His expertise is indisputable, but it also gives this book a certain amount of technicality, making it at times a bit difficult for the layman to follow his train of thought. And as an interested party, Reich naturally stresses the great merits of genetic research, and rightly so, but it seems to me that it is also important to warn against overestimation. This is because there are considerable limitations to this genetic research.
In the first place, it is extremely difficult to find usable DNA within fossils: it breaks down with time, and all the more in warm and humid areas. The consequence of this is that it is currently very difficult to extract DNA from fossils older than 100,000 years, or from areas that are tropical. Obviously this gives a bias. Reich himself has to admit that 90% of all fossils examined up to the end of 2017 come from western Eurasia; if that's not an imbalance, then I don't know. Perhaps this will be corrected over time (China is in the process of catching up), but still.
Moreover, the total number of fossils investigated is still relatively limited, and the techniques used are still in full development. Genetics and certainly Ancient Genetics is a relatively young science, and so you can see that in this book Reich has to radically contradict findings that were published in scientific journals even as recent as 2010. This should encourage vigilance and (healthy) skepticism. After all, it turns out that the interpretation of genetic research is always a statistical thing, in other words genetics is a probabilistic science, and so caution is all the more necessary.
Very little of this is noticeable in this book. Reich seems to me to be the typical example of a scientist who mainly sees the possibilities/opportunities and who remains fundamentally optimistic about revolutionary new insights and techniques. This pride is to some extent justified, for the new discoveries certainly are impressive, but it is best for anyone reading this book to remember that Reich's presentation is a very preliminary state of affairs, of a science that is constantly evolving.
Finally, there is the fundamental debate to what extent genetic material can be used to derive a complete and reliable picture of human history. Of course it cannot. Genetic material teaches us revolutionary new things about when and where human populations emerged, how they related to each other, and it also offers, in part, insight into social relationships, nutrition and diseases. But the entire world of human culture in the broadest sense of the word, of course, is not stored in the genes. Or are we going to indulge in the hackneyed nature-nurture debate again?
So yes, ancient DNA research certainly yields new insights, but you must always be cautious and compare them with findings from other sciences such as classical archeology, linguistics and sociology. In my discussion in my History Account on Goodreads, I highlight some of those new insights. See https://www.goodreads.com/review/show/2508806669. ( )

Fascinating and important ( )

Sensitive and timely book - sometimes it feels like a losing battle to educate others about genetics, but this book has a ton of nuance and really emphasizes that human population mixture is an integral part of human history. ( )

A broad survey of how ancient DNA analysis is changing our understanding of human development and migrations. I didn't find it inspiring, and would have liked a more focused and personal story. It feels like a bunch of Scientific American articles pasted together. (Every chapter is written to be standalone, so many basic facts are repeated ad nauseam.) And there isn't nearly enough about how the science was done. There are a few anecdotes, but very few, even though he was involved in a lot of the research. Reich is conflicted between writing for his peers (lots of namedropping, nothing bad ever said) and for a general audience. For example, he footnotes his sources, but he also writes them out in prose (e.g., "In August 20xx, X, Y and Z, in an article titled 'ABC' in 'Nature,' found that…") I found this bizarre. But the writing is always heavy-handed and never fluent, using ten words when one would do.

On the bright side, the graphics are fantastic. Reich does give a great summary of the field, and his opinions on where it is going. He very briefly explains some of the techniques and breakthroughs. ( )

Reich, David (2018). Who We Are and How We Got Here: Ancient DNA and the New Science of the Human Past. New York: Pantheon Books. ISBN: 9781101870334. Pagine 335. 9,38 €.

Questo è uno dei libri più importanti che ho letto negli ultimi dieci anni.

Purtroppo non anche uno dei più belli, perché la scrittura di David Reich a volte è un po’ faticosa. Inoltre, qui e là si perde in riflessioni etico-politiche, probabilmente necessarie, ma anche un po’ irrisolte e non del tutto convincenti. Ma andiamo con ordine: sulle implicazioni etico-politiche torneremo più avanti.
hhmi.com

David Reich è un genetista dedito alla ricerche sulla popolazione degli umani antichi, condotte utilizzando l’intero loro genoma (non esattamente facilissimo da recuperare) e applicando modelli statistico-matematici per studiarne le mutazioni. Con queste tecniche, lui e il suo gruppo sono stati in grado di proporre spiegazioni convincenti delle migrazioni e delle mescolanze delle diverse popolazioni, in epoca sia preistorica sia proto-storica e storica.

Il punto di partenza sono le ricerche di Luca Luigi Cavalli Sforza, morto ultra-novantaseienne nello scorso agosto. Cavalli Sforza ha scritto molti testi fondamentali, e io vi raccomando due grandi libri (Chi siamo. La storia della diversità umana, scritto insieme al figlio Francesco, pubblicato da Mondadori nel 1993 e ora riedito da Codice; e Geni, popoli e lingue, pubblicato da Adelphi nel 1996). A differenza di Reich, Cavalli Sforza aveva anche il dono della scrittura – almeno per quanto ricordo io, che questi libri li ho letti poco dopo la loro pubblicazione. Il problema è che la geniale sintesi di Cavalli Sforza, che porta a fattor comune conoscenze della genetica, della storia, dell’archeologia e della linguistica attraverso metodi statistici, necessariamente appare oggi superata sia dai progressi della genetica, sia da quelli della statistica. Quando iniziò i suoi studi, quasi sessant’anni fa, aveva a disposizione soltanto le proteine dei gruppi sanguigni; anche quando, dopo il 1990, poté contare sul codice genetico, le informazioni di cui disponeva erano limitate a pochi loci del genoma e comunque alle sole popolazioni attuali. Anche i metodi statistici utilizzati – analisi multivariate come le componenti principali e l’analisi dei gruppi – non erano sufficientemente sofisticate. Cavalli Sforza costruì un grande albero della radiazione della popolazione umana moderna (Homo sapiens) dall’Africa alle intere terre popolate, proponendo il modello della “diffusione demica”: in Europa, i primi agricoltori si sarebbero diffusi da sud-est a nord-ovest, incontrando via via popolazioni più antiche di cacciatori-raccoglitori e accumulando patrimonio genetico delle popolazioni precedenti, con cui si erano mescolati.

Questo modello, per quanto affascinante sotto il profilo intellettuale, è stato “falsificato” dall’avvento della rivoluzione del DNA antico, ed è su quest’ultima che si fonda il lavoro di David Reich e del suo gruppo (non va dimenticato il pioniere di queste tecniche, Svante Pääbo all’Istituto Max Planck per l’antropologia evolutiva di Lipsia). La combinazione di queste tecniche – in continuo progresso – e l’applicazione di modelli statistici più raffinati di quelli utilizzati da Cavalli Sforza permettono a David Reich e al suo gruppo di ricostruire molti aspetti della storia del popolamento del pianeta e delle migrazioni umane.

***

Il libro di cui stiamo parlando è suddiviso in tre parti.

La prima tratta della storia più antica della specie umana, quella che illustra come gli umani moderni – quelli migrati dall’Africa verso il vicino Oriente (in due ondate secondo il nuovo modello, la prima circa 130.000 anni fa, testimoniata da resti rinvenuti nell’attuale Israele, e la seconda 50-60.000 anni fa) – abbiano interagito, riproducendosi, con i Neanderthal prima dell’estinzione di questi ultimi circa 39.000 anni fa. Una seconda popolazione, quella dei recentemente scoperti Denisoviani, interagisce riproduttivamente con gli umani moderni circa nello stesso periiodo (49-44.000 anni fa). Il risultato sorprendente è che tutti gli attuali umani, salvo gli africani, portano tracce di DNA neanderthaliano e denisoviano nel loro genoma.

Per chi vuole maggiori dettagli, la parola allo stesso Reich:

Part I, “The Deep History of Our Species,” describes how the human genome not only provides all the information that a fertilized human egg needs to develop, but also contains within it the history of our species. Chapter 1, “How the Genome Explains Who We Are,” argues that the genome revolution has taught us about who we are as humans not by revealing the distinctive features of our biology compared to other animals but by uncovering the history of migrations and population mixtures that formed us. Chapter 2, “Encounters with Neanderthals,” reveals how the breakthrough technology of ancient DNA provided data from Neanderthals, our big-brained cousins, and showed how they interbred with the ancestors of all modern humans living outside of Africa. The chapter also explains how genetic data can be used to prove that ancient mixture between populations occurred. Chapter 3, “Ancient DNA Opens the Floodgates,” highlights how ancient DNA can reveal features of the past that no one had anticipated, starting with the discovery of the Denisovans, a previously unknown archaic population that had not been predicted by archaeologists and that mixed with the ancestors of present-day New Guineans. The sequencing of the Denisovan genome unleashed a cavalcade of discoveries of additional archaic populations and mixtures, and demonstrated unequivocally that population mixture is central to human nature. (pos. 419 ss.)

***

La seconda parte è dedicata a periodi più recenti, e analizza un insieme vasto di studi ed evidenze che aiutano a capire l’attuale origine delle popolazioni umane in diverse parti del globo: in particolare, l’Europa, l’India, le Americhe, l’Asia e l’Africa.

Diamo ancora la parola a Reich:

Part II, “How We Got to Where We Are Today,” is about how the genome revolution and ancient DNA have transformed our understanding of our own particular lineage of modern humans, and it takes readers on a tour around the world with population mixture as a unifying theme. Chapter 4, “Humanity’s Ghosts,” introduces the idea that we can reconstruct populations that no longer exist in unmixed form based on the bits of genetic material they have left behind in present-day people. Chapter 5, “The Making of Modern Europe,” explains how Europeans today descend from three highly divergent populations, which came together over the last nine thousand years in a way that archaeologists never anticipated before ancient DNA became available. Chapter 6, “The Collision That Formed India,” explains how the formation of South Asian populations parallels that of Europeans. In both cases, a mass migration of farmers from the Near East after nine thousand years ago mixed with previously established hunter-gatherers, and then a second mass migration from the Eurasian steppe after five thousand years ago brought a different kind of ancestry and probably Indo-European languages as well. Chapter 7, “In Search of Native American Ancestors,” shows how the analysis of modern and ancient DNA has demonstrated that Native American populations prior to the arrival of Europeans derive ancestry from multiple major pulses of migration from Asia. Chapter 8, “The Genomic Origins of East Asians,” describes how much of East Asian ancestry derives from major expansions of populations from the Chinese agricultural heartland. Chapter 9, “Rejoining Africa to the Human Story,” highlights how ancient DNA studies are beginning to peel back the veil on the deep history of the African continent drawn by the great expansions of farmers in the last few thousand years that overran or mixed with previously resident populations. (pos. 430 ss.)

Il punto fondamentale – presentato nel primo capitolo di questa parte – è che il modello dell’albero di classificazione, proposto dallo stesso Darwin (“The affinities of all the beings of the same class have sometimes been represented by a great tree….The green and budding twigs may represent existing species….The limbs divided into great branches, and these into lesser and lesser branches, were themselves once, when the tree was small, budding twigs.” – Darwin, Charles R. 1859. On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. London: John Murray), non è una metafora adeguata a rappresentare la complessità delle dinamiche storiche delle popolazioni e le relazioni tra le popolazioni umane contemporanee. La metafora dell’albero, infatti, implica che le popolazioni contemporanee derivino fondamentalmente da un solo antenato (il tronco) e si siano via via differenziatre senza possibilità di ricombinazione. Questo non è quello che è accaduto, e un semplice test permette di “falsificare” questa ipotesi:

The most natural way to test the tree model is to measure the frequencies of mutations in the genomes of two populations that we hypothesize have split from the same branch. If a tree model is correct, the frequencies of mutations in the two populations will have changed randomly since their separation from the other two more distantly related populations, and so the frequency differences between these two pairs of populations will be statistically independent. If a tree model is wrong, there will be a correlation between the frequency differences, pointing to the likelihood of mixture between the branches. (pos. 1622)

Personalmente, di questa seconda parte ho trovato particolarmente interessante la ricostruzione della preistoria europea (strettamente connessa alla “falsificazione” della teoria di Cavalli Sforza, di cui abbiamo parlato all’inizio). Le attuali popolazioni europee sono frutto di almeno tre popolazioni antiche: i cacciatori-raccoglitori diffusi nel continente 10.000 anni fa, gli agricoltori in migrazione dall’Anatolia tra 8.800 e 6.000 anni fa, e l’invasione degli Yamnaya, un popolo delle steppe dell’Asia centrale, tra 4.900 e 4.000 anni fa. Le evidenze genetiche a sostegno di quest’ultima ipotesi ridanno peso scientifico alle teorie originariamente sostenute da Marija Gimbutas negli anni Cinquanta. Da viva Marija Gimbutas è stata trattata dal mondo accademico più o meno come una strega, per i suoi studi sul matriarcato e sulla Grande Dea. Che ora la sua ipotesi sia riscattata dalla genetica è per me di grande soddisfazione.

Anche per quanto riguarda l’India, la narrazione dei Veda – il dio Indra su una carro di guerra trainato da cavalli sconfigge i nemici impuri, distruggendone le fortezze e assicurando al suo popolo, gli Arii, terre fertili – esce sostanzialmente confermata dalle evidenze raccolte da Reich e dal suo gruppo. Reich sta ben attento a non offendere il nazionalismo indiano, che rivendica l’assoluta originalità della cultura indiana e nega ogni ipotesi di migrazione o invasione: distingue tra ANI (Ancestral North Indians) e ASI (Ancestral South Indians). I primi discenderebbero approssimativamente in parti eguali da una popolazione della steppa legata alla lontana agli Yamnaya e da una popolazione di agricoltori di ascendenza iraniana incontrata dalla gente della steppa mentre si espandeva verso sud (tra i 5.000 e i 3.500 anni fa, e portatori delle lingue del ceppo indo-europeo). I secondi sarebbero il risultato della fusione di una popolazione di agricoltori proveniente in precedenza dall’Iran (per circa il 25%) e ( per circa il 75%) da cacciatori-raccoglitori stabilitisi in precedenza (non tanto i cacciatori-raccoglitori originari dell’India, quanto provenienti dall’Asia meridionale e probabilmente responsabili della diffusione dell’agricoltura dal Vicino oriente) (tra i 9.000 e i 4.000 anni fa, in movimento dall’Iran all’India meridionale, e portatori delle lingue del ceppo dravidico).

***

Infine, la terza e ultima parte tratta le implicazione della rivoluzione del DNA antico, con particolare attenzione agli aspetti delle “razze” (o meglio, come preferisce esprimersi Reich, dell’ascendenza – ancestry) e dell’identità. Alcune delle “difese” di Reich dall’accusa di reintrodurre il concetto di razza – tema evidentemente delicatissimo – non sono del tutto convincenti (e sono, tra l’altro, tra quelle maggiormente responsabili della mia considerazione che il libro è “mal scritto”). Probabilmente, però, gli studi (che sono in corso e si ampliano molto rapidamente) meritano un dibattito più ampio, e non limitato ai soli genetisti.

Molti hanno accolto il libro con favore: in particolare Jared Diamond (su questo blog ne abbiamo parlato più volte, soprattutto qui e qui) sul New York Times (“A Brand-New Version of Our Origin Story“), Peter Forbes sul Guardian (“Who We Are and How We Got Here by David Reich review – new findings from ancient DNA“) e Turi King su Nature (“Sex, power and ancient DNA | Turi King hails David Reich’s thrilling account of mapping humans through time and place“).

Tuttavia, un gruppo di 67 scienziati di diverse discipline accademica (prevalentemente al di fuori delle “scienze dure”) ha contestato apertamente il modo in cui Reich ha affrontato il tema della razza, e ne critica apertamente alcuni risultati su BuzzFeed (“How Not To Talk About Race And Genetics“): a me, personalmente, l’obiezione dei 67 non convince. Alcune delle argomentazioni mi sembrano speciose: è vero che il gene dell’anemia falciforme è prevalente in aree infestate della malaria (se non avesse anche dei vantaggi in quelle aree sarebbe stato spazzato via dall’evoluzione, come è accaduto in altre parti del mondo), ma una volta che esiste e si scopre statisticamente che è un carattere genetico distintivo di una sottopopolazione, il nome che si dà a differenze radicate nel genoma di diverse sottopopolazioni mi pare inessenziale. Reich sta ben attento a evitare la parola “razza”, consapevole delle connotazioni che il termine comporta. Questo, secondo me, è sufficiente a chiarire la discussione. I firmatari della lettera scrivono: “This doesn’t mean that genetic variation is unimportant; it is, but does not follow racial lines”. Intendiamoci: se per racial lines si intende il significato che i nazisti o i suprematisti bianchi danno al termine “razza”, d’accordo. Ma se sostituiamo all’aggettivo “razziale” l’aggettivo “ereditario”? Sapere che un rischio per la salute ha (anche, perché Reich non ha mai scritto o detto che non ci siano altri fattori o fonte di variazione) una componente genetica è irrilevante? siamo sicuri? se fossi un indiano dello jati dei Vysya sarei grato di sapere che ho un rischio relativamente elevato (4%) di avere un gene che inibisce la produzione della butilcolinesterasi e che prima di sottopormi a un’anestesia si devono prendere precauzioni specifiche, e presumibilmente non sarei troppo sensibile al modo in cui chiamare le evidenti linee ereditarie alla base del mio rischio clinico.

Anche l’argomentazione che “human beings are 99,5% genetically identical” (e già non capisco bene che cosa significa? che lo 0,5% degli umani ha un genoma diverso? che due esseri umani estratti a caso dalla popolazione hanno il 99,5% del genoma eguale? che hanno il 99,5% di probabilità di avere lo stesso genoma?) mi sembra discutibile: condividiamo con gli scimpanzé il 98% del genoma, ma non per questo ci rifiutiamo di classificarli sotto il profilo scientifico in due generi diversi (e questo non ha nulla a che fare con il come dovremmo trattare gli scimpanzé!). Quando poi scrivono che “Even ‘male’ and ‘female’ [scare quotes, niente meno!], which Reich invokes as obviously biologically meaningful, has important limitations” mi hanno proprio perso. Ho già scelto da che parte stare. Preferisco essere curato da un bravo oculista che mi definisce ipovedente o persino orbo-cecato, ma tiene pienamente conto di tutte le evidenze scientifiche a disposizione, che da un sensibile incompetente che usa eufemismi più politically correct, ma opera attivamente per ostacolare la ricerca scientifica in campi che ritiene politicamente delicati o macchiati da ideologie del passato (Reich riporta alcuni esempi di queste “sensibilità” che ostacolano sia la ricerca pura sia quella in campo medico, ad esempio presso i nativi americani).

Tanto più che la tesi finale di Reich è che non esistono popolazioni “pure”, ma che ogni umano moderno è il frutto di decine di migliaia di anni di rimescolamenti.

Vi invito anche a leggere l’articolo di Riccardo De Sanctis “La rivoluzione è nel Dna antico” pubblicato su il manifesto del 29 luglio 2018.

In questa parte ho trovato particolarmente interessante il capitolo sulle radici genetiche delle diseguaglianze, con particolare riferimento a quelle di genere. Nel genoma emerge in più situazioni una discrepanza tra i profili che emergono dal DNA mitocondriale, che si trasmette esclusivamente per linea femminile, da madre a figlia, e quelli che emergono dal cromosoma Y, presente soltanto nei maschi. Le evidenze indicano concordemente che i maschi invasori (e conquistatori) hanno sempre esercitato àil loro potere sulle donne delle popolazioni sottomesse, con la violenza, la forza o semplicemente l’esercizio del potere militare ed economico. Il caso più famoso – è un’antica narrazione che trova conferma genetica – è quello di Gengis Khan, ma presso gli afro-americani e le popolazioni non indo-europee dell’India affiorano nel genoma le stesse evidenze.

Di nuovo, lasciamo l’onere del riassunto di questa terza parte a David Reich.

Part III, “The Disruptive Genome,” focuses on the implications of the genome revolution for society. It offers some suggestions for how to conceive of our personal place in the world, our connection to the more than seven billion people who live on earth with us, and the even larger numbers of people who inhabit our past and future. Chapter 10, “The Genomics of Inequality,” shows how ancient DNA studies have revealed the deep history of inequality in social power among populations, between the sexes, and among individuals within a population, based on how that inequality determined success or failure of reproduction. Chapter 11, “The Genomics of Race and Identity,” argues that the orthodoxy that has emerged over the last century—the idea that human populations are all too closely related to each other for there to be substantial average biological differences among them—is no longer sustainable, while also showing that racist pictures of the world that have long been offered as alternatives are even more in conflict with the lessons of the genetic data. The chapter suggests a new way of conceiving the differences among human populations—a way informed by the genome revolution. Chapter 12, “The Future of Ancient DNA,” is a discussion of what comes next in the genome revolution. It argues that the genome revolution, with the help of ancient DNA, has realized Luca Cavalli-Sforza’s dream, emerging as a tool for investigating past populations that is no less useful than the traditional tools of archaeology and historical linguistics. Ancient DNA and the genome revolution can now answer a previously unresolvable question about the deep past: the question of what happened—how ancient peoples related to each other and how migrations contributed to the changes evident in the archaeological record. Ancient DNA should be liberating to archaeologists because with answers to these questions ( )

This should have been an exciting book, as it describes current research. Unfortunately, it instead demonstrates that performing research and communicating it outside the narrow domain of an academic paper are two quite different skills that often, as in this case, do not go hand in hand.

The first two parts (of three) are simply tedious, with paragraph after paragraph of prolix prose that quickly merges, at least in this reader's mind, into a stream of sameness. Every now and then one can pick out a point, but it's unfortunately rare.

One can only hope that this same work will be the subject of a book whose author understands the need in this kind of explanatory text to use interesting images to convey points, and to provide changes of voice in the prose, so that one doesn't simply lose interest in what should be a riveting subject.

As a scientist, the most disappointing feature is a near-complete lack of explanation of the statistics underlying the results. And as a non-biologist, the lack of a concise, readable explanation of what is actually being measured meant that I never really got a grasp of what these researchers are really doing in their labs.

The interesting parts (perhaps because they were far more readable) turned out not to be about the reticence shown by some people groups to taking part in these studies; and the rather short third section, which did not sit well with the sections that preceded it, could usefully have been expanded. ( )

An exciting look at a revolutionary innovation, this book was a revelation! The author is one of the foremost experts on human paleogenetics. an emerging field radically influencing traditional paleoanthropology. Over the last few years, DNA technology has advanced from the examination of the Y chromosome and mitochondrial DNA to whole genome analysis. The results are staggering. The history of the human migrations that colonized the globe over the last 50,000 years are rapidly becoming clearer. We see the primacy of the mixing of populations in human history. Even the ancient contributions to the human genome of other early human populations, for example the Neandertals and Denisovans, are not lost, but in fact detected and discerned.

In this book, Reich conveys the methodologies and recent results of this work. I am in awe that questions about human origins I have pondered for most of my life are rapidly being answered. As Reich indicates, much of the specifics in the book will change over the coming years due to the pace of research. But the insights in this book leave one well prepared to assimilate the wealth of discovery that is surely coming. To me, it’s essential reading.

4 and a half stars for the book itself, but five for importance! ( )