Review by Ruth Urben
Score: As a book 8/10 Reader satisfaction 9/10
Disclaimer. What follows is an incomplete and rapid summary of my initial understanding of the book after a single and too hasty read. The review, more of a synopsis, was written for an informal book group whose other members had not read the book. It was not written with the rigour that I think appropriate for publication. Consequently, it is very likely to contain omissions and errors of facts and understanding.
The book aims to demonstrate the power and contribution that genomic analysis (primarily since 2010) makes to understanding the populations and migration patterns of, primarily, modern humans throughout the world over the past 50,000 years. It does so in 3 sections:
Part 1 The Deep History of Our Species
Genomics; Neanderthals; Ancient DNA
Part 2 How We Got to Where We Are Today
Humanity’s Ghosts; Modern Europe; India; Native Americans; East Asians; Rejoining Africa
Part 3 The Disruptive Genome
Inequality; Race and Identity; The Future
I did not find the book an easy read: as a result, I underestimated how long it would take me to read it. It is not written for the general reader – unless a skim reader. To fully understand it, and particularly the first section, the reader needs a better understanding of genomics and genomic statistical analyses and predictions than I have. In the absence of this familiarity, the reader could skip large portions of the text and rely only on the succinct and comprehensible diagrams of population groups, their separation, recombinations and migrations against time, and on the summarising subsections within each chapter.
With the above caveat, the book is a fascinating account of the current understanding of the ancestry, sequence and interrelations of present, historic, and prehistoric human populations; how DNA analysis has confirmed/disproved earlier understandings; how it has predicted ‘ghost’ populations that must have existed despite the absence of any physical evidence (which may emerge); how it can point to intra-population segregation and power differentials; its potential in the future; and the political and cultural sensitivities that can limit its potential.
Given that the author can only write of the present understanding that genomics has enabled – which has changed earlier understandings, there must be a question of whether future technologies may in their turn radically change the answers to the title’s implicit questions ‘Who are we? How did we arrive here?’
Part 1.
Genomics is based on the analysis of human DNA, its sequence of genes on the chromosome (and mitochondria), the rates of change of sequence lengths (due to splitting and recombination of chromosomes each generation)), and the rate of gene mutation over generations (Please correct me where I am wrong). This allows similarities and differences between population groups to be compared and hence the closeness of affiliation between population groups, and allows estimates to be made of how long ago population groups have split off from an ancestral population and/or interbred with each other.
7m-5mya Chimpanzee – human split
3.2mya Lucy (Australopithecus)
1.80mya Homo fossils in Eurasia (Georgia)
770,-550,000ya Neanderthal/modern human split
330,000ya Oldest fossils with anatomically modern human features (Morocco)
320,000ya Most recent shared ancestor of all modern humans;
280,000ya San group. West Africans split from San line
160,000 Mitochondrial ‘Eve’: most recent shared maternal ancestor
120,000 East Africans split from West African line
80,000 West Eurasians split from East African line
50,000 East Asians split from West Eurasian line
40,000 Native Americans split from East Asian line.
Neanderthal genes, very low/none in African populations; developed mostly in Eurasia? At biological limit of breeding compatibility with modern humans when the two populations reencountered 120,000 and 50,000ya.
Neanderthals survived and redominated after the first influx of modern humans from Africa but not the second influx
1m-800,000ya Denisovans split from common ancestral line with Neanderthal/modern human
770,-550,000ya Neanderthal/modern human split
700,-50,000ya ‘Hobbits’ of Flores
400,-270,000 Siberian Denisovan and Australo Denisovan split
54,-49,000 Neanderthal-non-African ancestors (modern human) interbreeding
49,-44,000 Denisovan-modern human interbreeding
Part 2 How we got to where we are.
West Eurasians
39,000ya Neanderthals die out in Europe
37,-35,000 Split of main European hunter-gatherers
33,-22,000 Gravettian culture/ancestry spread from East through Europe
25,-19,000 Last Glacial maximum
19,-14,000 Magdelenian culture/ancestry spread from SouthWest through Europe
14,-8,000 Warming period; new hunter gatherers spread from South East into Europe
11,500 Farming develops in 2 distinct Near East locations (Iran, Anatolia)
10,000 West Eurasian populations merge
10,-5,000 Hunter gatherers persist in Europe
8,8-6,00 Farming from Anatolia spreads into Europe
5,-4,000 Stonehenge built, Yamnaya steppe herding culture spreads across Caspian steppe
4,9-4,300 People with steppe ancestry replace 70% of Central European population
4,5-4,300 People with steppe ancestry replace 30% of Iberian population
4,4-4,200 People with steppe ancestry replace 90% of British population
3,500 Second influx of Anatolian migrants, only traceable in Greece
Eurasians a Heinz 57 population. Nazi attempt to link to a dominant ‘Aryan’ culture to justify their territorial takeover of Poland, repression of Jews etc misguided. No such ‘pure’ lineage exists
India
9,000ya Farming from Iran spreads into Indus Valley
5,000 Farming into peninsular India from East and West
5,000 Yamnaya expansion in steppe
4,3-3,800 Indus Valley civilisation
4,-3,000 Formation of Ancestral North Indians (ancestry Europe, Near East, Central Asia ie current West Eurasians) leading to Indo-European language, and more steppe ancestry)
Formation of Ancestral South Indians (closest to East Asians but long separated, ancestry an early lineage contributing to S Asians but nowhere else and not existing today leading to Dravidian language, more S. Indian ancestry)
4,-2,000 Massive mixture of 2 ancestral lines and formation of N Indians, S Indians
3,800 Shift of population centre eastwards from Indus valley
3,500 Rig Veda -oldest Indian text describing influx of new population
3,000 Strong endogamy begins (facilitating ongoing segregation of multiple sub-groups (caste, jati)
Due to socially/culturally maintained segregation, India effectively consists of multiple sub-populations with genetically differences but all with more/less steppe and S. Indian ancestry. Very different from the mixing within West Eurasia and the openness of the Han Chinese, who are one large single population.
Pure (little) Andaman Islanders the exception – no NI ancestry but descendants of early and now vanished East Asian population, Austro-asiatic language.
Politics in India sensitive to any admission of population influx from West Europe/Eurasia: diplomatic wording necessary (hence Ancestral North Indian nomenclature). Freedom to completely express genome findings a little constrained. No group in mainland India is genetically ‘pure’.
Native Americans
Uncertain date of arrival of Ancestral Population Y
16,000 ya Coastal route southwards from Alaska opens
>15,000ya Minimum (latest) date for arrival from Asia
14,6-14,200 human presence in central/south America
13,000 Ice-free land route opens
13,-11,000ya Modern humans spread across temperate America
12,600 First American ancestry
8,500 Kennewick skeleton
6,000 Maize domestication
5,-4,000 First civilizations
5,000 Arctic small tool tradition spreads to America; Paleo-Eskimos established
2,-1,000 Na-Dene speakers (2nd language group) spread in Western North America
1,000 Ancestors of Eskimo-Aleut speakers (3rd language group) enter Arctic America from Asia
500ya Arrival of Europeans and Africans and population structure of Americas transformed.
Initially thought all Native Americans descended from single southward moving population. Genomics showed early population split in two but migration route and timing of second group unknown. Sub-groups split off and settled as main population moved south and little subsequent remixture thereafter. Distinct languages and physical differences/features developed between segregated groups through recombinations/mutations over time. Very different from the constant mixing of sub-groups in West Eurasia. A more recent analysis suggests that some of the isolated Amazonian AmerIndians may have ancestral linkages with Australasians.
Possibility of return migration from northern America back to Asia-Siberia (Chukchi language group) and then back again to Alaska.
Ethical and cultural sensitivities constrain genomic research on current and (pre-)historic AmerIndians and so there is inadequate data to further understand early histories of Native Americans. Abuse of samples by earlier researchers resulted in loss of trust by Native Americans and withdrawal of permission to sample from present or earlier individuals. Reich debates where responsibility lies: to respect views of present Native Americans or to respect the benefit that deeper understanding of history and origins can bring to humanity (and specific medical benefits re. identifying and addressing genetic causes of disease arising from inbreeding within small population groups [population bottlenecks).
East Asia and the Pacific
1.7mya Minimum date of first humans in East Asia (Homo erectus in China; similarly in Indonesia)
700,-50,000ya ‘Hobbits’ of Flores.
Early dispersal of modern humans to East Asia before main post 50,000ya dispersal
400,-270,000 Siberian Denisovan and Australo Denisovan split
54,-49,000 Neanderthal-non-African ancestors (modern human) interbreeding
49,-44,000 Denisovan-ancestors of Australians and Papuans interbreeding
47,000ya Modern humans from SE Asia in Australia + first humans in Papua (archaeological evidence)
40,000ya Ancient DNA from near Beijing is same lineage as present East Asians
9,000 (Independent) Agriculture begins in Yangtse and Yellow River valleys
5,000 Agriculture spreads from 2 centres in China (dryland cropping (Yellow River), rice (Yangtze River), rice spreading overland to Vietnam, Thailand, later India, and by sea to Taiwan)
4,-3,300 1st Austronesian human expansion from Taiwan into southwest Pacific islands
2,400 Later migration SE spread (the first) Papuan ancestry to SW Pacific islands
2,000 Massive expansion of Han
800 Austronesian expansion at maximum extent
Unknown if earliest East Asian humans contributed ancestry to today’s population.
SE Asia and Australia show no upper paleolithic technology – the split between West Eurasian and East Asian lineage could have predated the technology and could indicate an earlier dispersal of modern humans before the accepted 50,000ya (taking a southern route, skirting India) even if they left little genetic impact on ancestry of current population. Some evidence of an earlier c 70,000ya split between Australo-aboriginal lineage (to use southern route and the c 30,000ya split between East Asians and European lineages. Consensus that within 5,000 yrs (49,-44,000ya) West Eurasian and East Eurasian lineage split first, last major split was lineage of Papuans/Australo Aborigines from East Eurasian lineage. All ancestry of modern East Asians/Australians from same group of humans that displaced early Europeans.
Spread of Chinese agriculture; spread of languages; = spread of people?
2 divergent ancestral (ghost) lineages contributing to East Asians – Yellow River ghost popn spreading W to Tibet, Yangtze River ghost popn spreading south
Export of genomic samples from Chinese discouraged and own genomic research capability was lagging until its recent update to state of the art. Flood of data (and answers) now expected.
Rejoining Africa
Genomics suggest that 2 archaic populations might have mixed and all Africans have ancestry from both in different amounts (W. Africans having more lineage from Archaic popn 1 than do non-African popns.
Major mixture well before 50,000ya – between 2 Archaic lineages? 2 Modern lineages? Or 1 Archaic, 1 Modern? Homo naledi in S Africa a candidate?
Possible later westwards movement of/mixing with Near East humans.
Malaria resistance (+sickle cell anaemia) has arisen independently (at 3 different genetic locations and different gene sequences) in Far West, West Central and Central Africa (Senegal, Niger, ?Congo?); lactose tolerance has arisen independently (same gene but 2 different mutations) in 2 herder popns (Fulani (N.Africa), Maasai (E.Africa)
Expansion of groups within Africa. San contracted. Huge Bantu expansion c 4,000ya from Niger-Cameroun, South first, later NE. Later, Nilo Saharan expansion W and S(E))
Also genetic influx from Near East agriculturalists 10,000ya?
Also West Eurasian admixture from Iranian farmers in Bronze Age.
Later, c 1,8-500ya, spread of Khoe Kwadi languages from East Africa (by E African cattle herders) to Southern Africa (but genetic linkages with Ethiopia suggesting Archaic herder popn from N that brought language and mixed with E. African popn)
Since 1,400CE, extensive recent mixing of popns due to slave trading activities.
Much mixing of groups within Africa but also segregation of some popns (eg different mutations for malaria resistance and for lactose tolerance in different African popns).
Part 3 The Disruptive Genome
In this final part, Reich expands on the examples that are interspersed throughout the book to demonstrate how genomic research has revealed the societal values and structures in different human groups and their interaction with genome sequence inheritance and spread.
The Genomics of Inequality
Typically invading populations may impose a societal structure with themselves at apex e.g. Portuguese into S. America. Apex male genome spreads as breed with indigenous females / African slaves. Indigenous male ancestry discriminated against. 38% Americans have male European ancestry: 10% have female European ancestry.
Hundreds of millions of Americans have black ancestry.
Gengis Khan: 1 male has many millions of direct male line descendants across Mongol empire.
Yamnaya invasion similar male genomic bias.
Pacific Island cultures with matriarchal culture, female genome ancestry dominates over male ancestry.
As genomic research technology develops further, more evidence of (pre)historic inequalities will be found and understood.
Do we say sex power bias inherent to human culture and accept it? Or do we struggle against it and try and redress it, as humanity at its best is able to do?
The Genomics of Race and Identity
Unbiased and genome based description of and research into racial / genetic popn group differences e.g. in disease incidence between genetic groups is hampered by anthropological school that believes this promotes racism and hampered by sociologists who disagree with the idea of ‘racial’ differences. Race seen as a social concept, given the greater genetic similarity between populations and the greater influence of society and culture (85% vs 15% genetic) on individual behaviour and achievements. This results in attempts to ban any such genome based research, thereby preventing research to fully understand the genetic basis of the defects and the identification of cures/treatment/preventative measures for these.
If scientists don’t present a rational framework for discussing ‘racial’ differences, pseudo-scientists will (irrational, not evidence based). How does humanity best prepare for the recognition that there are genetic ‘racial’ differences that do/may express themselves in cognitive and behavioural differences but without evaluating as better/worse – just different. Humans to commit to treating everyone equally and accord all equal rights.
Reich views genomic research as destroying any political ideologies of intrinsic superiority of current nations / population groups – eg Nazis and Aryan inheritance; eg white American supremacy and ‘ownership’ of America (Trump’s inauguration speech?). Genomics presents the human history of continuous mixing and movement and common ancestry of human groups. Provides us with a shared history incompatible with racism and nationalism. Makes us realise we are all entitled equally to our human heritage.
The Future of Ancient DNA
1949 – C14 the new technology revealing human history for past 50,000 yrs. Showed separate locations of innovation, not all from Middle and Near East. Genomics the new technology providing new and unimagined vistas into deep past and details of population movements. Also into detailed understanding of population sizes, local movements within past 1000yrs, rates of genetic adaptations/evolutionary change (rapid increase in infant size and British women’s hip size) . Presently genomic data is highly Eurocentric (90%of samples from West Eurasia). This is and will be changing as analytical capacity develops and more archaeological finds come from other regions.
Cultural considerations and sensitivities re disturbing and using ancient skeletons for research. Would they have wished it? Is it contrary to cultural practices. How can these be known for ancient time? What is the moral balance of this disturbance of one or some individuals vs the benefits to humanity from genomic research?
These final sections, which do repeat some of the views and conclusions that the author has already presented, suggest the author as a committed researcher and as a deeply humane man.
As a committed researcher into the genomic truth, Reich is frustrated by the cultural and societal beliefs, dogmas and values which close some avenues of genomic research and close people’s eyes to evidence based information.
As a seemingly deeply humane man, Reich’s vision of genomic research is as a force for good that can contribute to overcoming tribalism, nationalism and discrimination, in addition to its physical benefits of genome targeted health interventions, by its power to illuminate human history, to reveal the ancestral commonality of humans and to reveal the genetic basis for human differences. Others may rightly be more cautious about humanity’s ability to use the genomic research findings to exploit or discriminate against the less powerful.
Of Books, Bikes & Islands 