The 10,000 Year Explosion
Encyclopedia
The 10,000 Year Explosion: How Civilization Accelerated Human Evolution is a 2009 book by anthropologists Gregory Cochran
and Henry Harpending
. Starting with their own take on the conventional wisdom
that the evolutionary process
stopped when modern humans appeared, the authors explain the genetic
basis of their view that human evolution is accelerating, illustrating it with some unexpected examples.
Cochran and Harpending put forward the idea that the development of agriculture
has caused an enormous increase in the rate of human evolution
, including numerous evolutionary adaptations to the different challenges and lifestyles that resulted. Moreover, they argue that these adaptations have varied across different human populations, depending on factors such as when the various groups developed agriculture, and the extent to which they mixed genetically with other population groups.
Such changes, they argue, include not just well-known physical and biological adaptations such as skin colour, disease resistance, and lactose tolerance
, but also personality and cognitive
adaptations that are starting to emerge from genetic research. These may include tendencies towards (for example) reduced physical endurance, enhanced long-term planning, or increased docility, all of which may have been counter-productive in hunter-gatherer
societies, but become favoured adaptations in a world of agriculture and its resulting trade, governments and urbanization
. These adaptations are even more important in the modern world, and have helped shape today's nation states. The authors speculate that the scientific
and Industrial Revolution
s came about in part due to genetic changes in Europe over the past millennium, the absence of which had limited the progress of science in Ancient Greece
.
The authors suggest we would expect to see fewer adaptive changes among the Amerindians and sub-Saharan Africans, who have farmed for the shortest times and were genetically isolated from older civilizations by geographical barriers. In groups that had remained foragers, such as the Australian Aborigines
, there would presumably be no such adaptations at all. And so it proves. Indigenous Australians
and many native Americans
have characteristic health problems today when exposed to Western diets. Similarly, Amerindians, Aboriginals, and Polynesians
, for example, had experienced very little infectious disease. They had not evolved immunities as did many Old World
dwellers, and were decimated upon contact with the wider world.
greatly accelerated increases in the rates of evolution. The authors begin their discussion by quoting the conventional wisdom:
This had become the established viewpoint - when modern humans appeared, evolution was essentially over. The received wisdom is based on the doctrine
that human minds are the same, everywhere: Bastian
's Psychic Unity of Mankind. Unfortunately, the authors continue, this is no more than wishful thinking. Were it true, human bodies would also be the same worldwide, which clearly they are not. Finns cannot be mistaken for Zulus, nor Zulus for Finns. Not only are there strong reasons to believe that significant human evolution is theoretically possible, or even likely; it is completely obvious that it has taken place, assert the authors, since people look different from one another.
The first four of the book’s seven chapters serve as a preamble to the final three. First, Cochran and Harpending present evidence for recent, accelerated human evolution after the invention of agriculture. In itself, this argument represents a paradigm shift
, albeit one that now has clear data to back it up. The International HapMap Project
and other studies have shown that selection
is ongoing and has accelerated over time. This has been a key discovery in human biology, and Cochran and Harpending, building on their own work and that of others such as John Hawks
of the University of Wisconsin-Madison, tie the advent of agriculture — and the selection pressures
resulting from the new diets, new modes of habitation, new animal neighbors, and new modes of living that agriculture made possible — to this accelerating evolution.
writes that Cochran and Harpending continue to refute conventional wisdom in their discussion of the Neandertals. For natural selection to have a chance, they argue, there need to be favourable mutations, or favourable combinations of existing allele
s such as genes
for blue eyes or pale skin. Cochran and Harpending concentrate on the Neolithic farming revolution
as the beginning of major population expansions that provided enough mutations to accelerate genetic change. Infectious diseases were another consequence of the early urban populations
and soon became a new source of selection pressures. The origins of many recently adapted genes have now been traced to this period, creating effects such as regional differences in skin colour and skeletal gracility
. Adaptations may have sacrificed muscle strength for higher intelligence and less aggressive human behaviours. By 5000 years ago, the authors estimate that adaptive alleles were coming into existence at a rate about 100 times faster than during the Pleistocene. This is the ‘‘explosion’’ of the book’s title.
Research cited by Cochran and Harpending provides evidence of genetic mixing
between modern humans and an ancient Homo
lineage such as the Neanderthals. It supports the idea that modern humans could have benefited by acquiring adaptive alleles evolved by our Neanderthal relatives - in this case, microcephalin
, an adaptive allele associated with brain development. Microcephalin (MCPH1) regulates brain size, and has evolved under strong positive selection in the human evolutionary lineage. One genetic variant of Microcephalin, which arose about 37,000 years ago, increased its frequency in modern humans too rapidly to be compatible with neutral
genetic drift
. As anatomically modern humans emerged from Africa and spread across the globe, the “indigenous” Homo populations they encountered had already inhabited their respective regions for long periods of time and might have been better adapted to the local environments than the colonizers. It follows that modern humans, although probably superior in their own way, could have benefited from adaptive alleles gained by interbreeding with the populations they replaced, as appears to be the case for the brain size-determining gene microcephalin.
s, thereby increasing opportunity for evolutionary change under natural selection. The spread of rapidly expanding populations eventually outpaced the spread of favourable mutations under selection in those populations, so for the first time in human history favourable mutations could not fully disperse throughout the human species. In addition, of course, selection pressures changed once farming was adopted, favouring distinctive adaptations in different geographic areas.
Farming, rather than just reduced sunlight, may have helped trigger pale skin in Europeans. In a 2007 study, almost all Africans and East Asians have one allele of the SLC24A5
gene, whereas 98% of the Europeans studied had the other. These data suggest that a selective sweep
occurred as recently as 5,300 to 6,000 years ago, replacing darker skins with light skins at astonishing speed. It implies that Europeans had been dark-skinned for tens of thousands of years. Several decades ago, Stanford's Cavalli-Sforza
had argued that European hunter-gatherers, herders and fishers could have survived from the vitamin D content of their diet, alone. Only when farming took hold did Europeans - replacing meat and fish with grain
- need to absorb more sunlight to produce the vitamin in their skin. Other writers, including Darwin
, Miller
, and Dawkins
, have proposed that skin colour changes were driven by sexual selection
. Cochran and Harpending reject the sexual selection idea when used to imply that race is no more than skin deep ("perhaps little more than a fad"), pointing out that experts can easily determine race from skeletal evidence alone.
of human migration, ignoring their functions. The authors support such research, but argue for a more complete understanding of the geographic distributions of genes. Where the usual geographical analysis treats the distribution of genes as an effect of history, in the authors' view, the genes themselves are a major cause: Two variants in the same gene do not necessarily have the same effect, and their relative, selective benefits will control the spread of genes through populations in both space and time.
legend in Britain to the Spanish colonization of the Americas
. Others have attempted this, for example in Jared Diamond’s Guns, Germs, and Steel
. But, according to Kelleher, Cochran and Harpending go one better than Diamond. Where he was content with environmental determinism
, opposing the roles of human biology and population differences, Cochran and Harpending embrace them both. Their discussions of gene flow becomes the core of an argument for biology as central to history, and the backdrop for the book’s two major hypotheses.
The first seeks to resolve a longstanding debate in historical linguistics
by making a case for the Kurgan hypothesis
on the origins of the Indo-European language group
. The Kurgan theory holds that Indo-European speakers came from lands between the Black
and Caspian
seas before spreading their language by conquest. The authors suggest that dairy farming and a complementary adaptation - the ability to digest lactose in adulthood - lie behind their conquests. With a walking food source, the milk-drinking warriors defeated their plant-growing neighbours. Drinking milk, from cows, horses, or camels, is a behavior shared by many of history’s greatest conquering peoples, whether Kurgans, Scythians, Arabs, or Mongols
. Without continuing evolution, the ability to digest milk could never have arisen. In fact, it has done so several times, in different ways, in various places, and it has helped shape human history. Kelleher comments that the authors’ argument makes it difficult to imagine the language in which their book would have been written, were it not for the ability to digest milk.
have a mean
IQ
so much higher than that of the population in general. This argument had been published previously in an earlier paper that attracted wide media coverage, generating extensive criticism and praise. This final chapter prior to the book's conclusion has been described as a consistent, thorough, biological history — or perhaps, better, a consistent biological hypothesis of a specific history, and a falsifiable one to boot.
In Seed
Magazine, T.J. Kelleher, describes this book as a manifesto for and example of a new kind of history, a biological history - and not just of the prehistoric era. Kelleher writes that, covering broad ground over human history and prehistory, the authors argue for the singular importance of genes in human history, not just as markers of it, but also as its makers.
In respect of Askenazi Jews, however, Kelleher feels that Cochran and Harpending’s impatience to get to the core of their argument drives them to quickly dismiss most of their critics — too quickly, given the long and rancorous debate in the United States about the genetic heritability of intelligence. It would have benefited the book to consider those criticisms at greater length.
Gregory Cochran
Gregory M. Cochran is a physicist and adjunct professor of anthropology at the University of Utah who has developed some new ideas in evolutionary medicine and genetic anthropology. Cochran is known for several controversial theories....
and Henry Harpending
Henry Harpending
Henry C. Harpending is an anthropologist and population geneticist at the University of Utah, where he is a distinguished professor...
. Starting with their own take on the conventional wisdom
Conventional wisdom
Conventional wisdom is a term used to describe ideas or explanations that are generally accepted as true by the public or by experts in a field. Such ideas or explanations, though widely held, are unexamined. Unqualified societal discourse preserves the status quo. It codifies existing social...
that the evolutionary process
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
stopped when modern humans appeared, the authors explain the genetic
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
basis of their view that human evolution is accelerating, illustrating it with some unexpected examples.
Cochran and Harpending put forward the idea that the development of agriculture
Neolithic Revolution
The Neolithic Revolution was the first agricultural revolution. It was the transition from hunting and gathering to agriculture and settlement. Archaeological data indicates that various forms of plants and animal domestication evolved independently in 6 separate locations worldwide circa...
has caused an enormous increase in the rate of human evolution
Human evolution
Human evolution refers to the evolutionary history of the genus Homo, including the emergence of Homo sapiens as a distinct species and as a unique category of hominids and mammals...
, including numerous evolutionary adaptations to the different challenges and lifestyles that resulted. Moreover, they argue that these adaptations have varied across different human populations, depending on factors such as when the various groups developed agriculture, and the extent to which they mixed genetically with other population groups.
Such changes, they argue, include not just well-known physical and biological adaptations such as skin colour, disease resistance, and lactose tolerance
Lactose intolerance
Lactose intolerance, also called lactase deficiency or hypolactasia, is the inability to digest and metabolize lactose, a sugar found in milk...
, but also personality and cognitive
Cognition
In science, cognition refers to mental processes. These processes include attention, remembering, producing and understanding language, solving problems, and making decisions. Cognition is studied in various disciplines such as psychology, philosophy, linguistics, and computer science...
adaptations that are starting to emerge from genetic research. These may include tendencies towards (for example) reduced physical endurance, enhanced long-term planning, or increased docility, all of which may have been counter-productive in hunter-gatherer
Hunter-gatherer
A hunter-gatherer or forage society is one in which most or all food is obtained from wild plants and animals, in contrast to agricultural societies which rely mainly on domesticated species. Hunting and gathering was the ancestral subsistence mode of Homo, and all modern humans were...
societies, but become favoured adaptations in a world of agriculture and its resulting trade, governments and urbanization
Urbanization
Urbanization, urbanisation or urban drift is the physical growth of urban areas as a result of global change. The United Nations projected that half of the world's population would live in urban areas at the end of 2008....
. These adaptations are even more important in the modern world, and have helped shape today's nation states. The authors speculate that the scientific
Scientific revolution
The Scientific Revolution is an era associated primarily with the 16th and 17th centuries during which new ideas and knowledge in physics, astronomy, biology, medicine and chemistry transformed medieval and ancient views of nature and laid the foundations for modern science...
and Industrial Revolution
Industrial Revolution
The Industrial Revolution was a period from the 18th to the 19th century where major changes in agriculture, manufacturing, mining, transportation, and technology had a profound effect on the social, economic and cultural conditions of the times...
s came about in part due to genetic changes in Europe over the past millennium, the absence of which had limited the progress of science in Ancient Greece
Ancient Greece
Ancient Greece is a civilization belonging to a period of Greek history that lasted from the Archaic period of the 8th to 6th centuries BC to the end of antiquity. Immediately following this period was the beginning of the Early Middle Ages and the Byzantine era. Included in Ancient Greece is the...
.
The authors suggest we would expect to see fewer adaptive changes among the Amerindians and sub-Saharan Africans, who have farmed for the shortest times and were genetically isolated from older civilizations by geographical barriers. In groups that had remained foragers, such as the Australian Aborigines
Australian Aborigines
Australian Aborigines , also called Aboriginal Australians, from the latin ab originem , are people who are indigenous to most of the Australian continentthat is, to mainland Australia and the island of Tasmania...
, there would presumably be no such adaptations at all. And so it proves. Indigenous Australians
Indigenous Australians
Indigenous Australians are the original inhabitants of the Australian continent and nearby islands. The Aboriginal Indigenous Australians migrated from the Indian continent around 75,000 to 100,000 years ago....
and many native Americans
Indigenous peoples of the Americas
The indigenous peoples of the Americas are the pre-Columbian inhabitants of North and South America, their descendants and other ethnic groups who are identified with those peoples. Indigenous peoples are known in Canada as Aboriginal peoples, and in the United States as Native Americans...
have characteristic health problems today when exposed to Western diets. Similarly, Amerindians, Aboriginals, and Polynesians
Polynesians
The Polynesian peoples is a grouping of various ethnic groups that speak Polynesian languages, a branch of the Oceanic languages within the Austronesian languages, and inhabit Polynesia. They number approximately 1,500,000 people...
, for example, had experienced very little infectious disease. They had not evolved immunities as did many Old World
Old World
The Old World consists of those parts of the world known to classical antiquity and the European Middle Ages. It is used in the context of, and contrast with, the "New World" ....
dwellers, and were decimated upon contact with the wider world.
Overview
The book's thesis is that human civilisationCivilization
Civilization is a sometimes controversial term that has been used in several related ways. Primarily, the term has been used to refer to the material and instrumental side of human cultures that are complex in terms of technology, science, and division of labor. Such civilizations are generally...
greatly accelerated increases in the rates of evolution. The authors begin their discussion by quoting the conventional wisdom:
- Something must have happened to weaken the selective pressure drastically. We cannot escape the conclusion that man’s evolution towards manness suddenly came to a halt. --Ernst MayrErnst MayrErnst Walter Mayr was one of the 20th century's leading evolutionary biologists. He was also a renowned taxonomist, tropical explorer, ornithologist, historian of science, and naturalist...
, 1963.
- There’s been no biological change in humans in 40,000 or 50,000 years. Everything we call culture and civilization we’ve built with the same body and brain --Stephen J. Gould, 2000.
This had become the established viewpoint - when modern humans appeared, evolution was essentially over. The received wisdom is based on the doctrine
Doctrine
Doctrine is a codification of beliefs or a body of teachings or instructions, taught principles or positions, as the body of teachings in a branch of knowledge or belief system...
that human minds are the same, everywhere: Bastian
Adolf Bastian
Adolf Bastian was a 19th century polymath best remembered for his contributions to the development of ethnography and the development of anthropology as a discipline...
's Psychic Unity of Mankind. Unfortunately, the authors continue, this is no more than wishful thinking. Were it true, human bodies would also be the same worldwide, which clearly they are not. Finns cannot be mistaken for Zulus, nor Zulus for Finns. Not only are there strong reasons to believe that significant human evolution is theoretically possible, or even likely; it is completely obvious that it has taken place, assert the authors, since people look different from one another.
The first four of the book’s seven chapters serve as a preamble to the final three. First, Cochran and Harpending present evidence for recent, accelerated human evolution after the invention of agriculture. In itself, this argument represents a paradigm shift
Paradigm shift
A Paradigm shift is, according to Thomas Kuhn in his influential book The Structure of Scientific Revolutions , a change in the basic assumptions, or paradigms, within the ruling theory of science...
, albeit one that now has clear data to back it up. The International HapMap Project
International HapMap Project
The International HapMap Project is an organization that aims to develop a haplotype map of the human genome, which will describe the common patterns of human genetic variation. HapMap is a key resource for researchers to find genetic variants affecting health, disease and responses to drugs and...
and other studies have shown that selection
Selection
In the context of evolution, certain traits or alleles of genes segregating within a population may be subject to selection. Under selection, individuals with advantageous or "adaptive" traits tend to be more successful than their peers reproductively—meaning they contribute more offspring to the...
is ongoing and has accelerated over time. This has been a key discovery in human biology, and Cochran and Harpending, building on their own work and that of others such as John Hawks
John D. Hawks
John Hawks is a professor of Anthropology at the University of Wisconsin–Madison. He also is the author of a widely read paleoanthropology blog.-Biography:...
of the University of Wisconsin-Madison, tie the advent of agriculture — and the selection pressures
Evolutionary pressure
Any cause that reduces reproductive success in a proportion of a population, potentially exerts evolutionary pressure or selection pressure. With sufficient pressure, inherited traits that mitigate its effects - even if they would be deleterious in other circumstances - can become widely spread...
resulting from the new diets, new modes of habitation, new animal neighbors, and new modes of living that agriculture made possible — to this accelerating evolution.
Neanderthals
WolpoffMilford H. Wolpoff
Milford H. Wolpoff is a paleoanthropologist, and since 1977, a professor of anthropology and adjunct associate research scientist, Museum of Anthropology at the University of Michigan...
writes that Cochran and Harpending continue to refute conventional wisdom in their discussion of the Neandertals. For natural selection to have a chance, they argue, there need to be favourable mutations, or favourable combinations of existing allele
Allele
An allele is one of two or more forms of a gene or a genetic locus . "Allel" is an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation...
s such as genes
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
for blue eyes or pale skin. Cochran and Harpending concentrate on the Neolithic farming revolution
Neolithic Revolution
The Neolithic Revolution was the first agricultural revolution. It was the transition from hunting and gathering to agriculture and settlement. Archaeological data indicates that various forms of plants and animal domestication evolved independently in 6 separate locations worldwide circa...
as the beginning of major population expansions that provided enough mutations to accelerate genetic change. Infectious diseases were another consequence of the early urban populations
Cradle of Civilization
The cradle of civilization is a term referring to any of the possible locations for the emergence of civilization.It is usually applied to the Ancient Near Eastern Chalcolithic , especially in the Fertile Crescent , but also extended to sites in Armenia, and the Persian Plateau, besides other Asian...
and soon became a new source of selection pressures. The origins of many recently adapted genes have now been traced to this period, creating effects such as regional differences in skin colour and skeletal gracility
Gracile
The English word "gracile" means slender. It derives from the Latin adjective gracilis , or gracile which in either form means slender, and when transferred for example to discourse, takes the sense of "without ornament", "simple", or various similar connotations.In his famous "Glossary of Botanic...
. Adaptations may have sacrificed muscle strength for higher intelligence and less aggressive human behaviours. By 5000 years ago, the authors estimate that adaptive alleles were coming into existence at a rate about 100 times faster than during the Pleistocene. This is the ‘‘explosion’’ of the book’s title.
Research cited by Cochran and Harpending provides evidence of genetic mixing
Genetic admixture
Genetic admixture occurs when individuals from two or more previously separated populations begin interbreeding. Admixture results in the introduction of new genetic lineages into a population. It has been known to slow local adaptation by introducing foreign, unadapted genotypes...
between modern humans and an ancient Homo
Archaic Homo sapiens
Archaic Homo sapiens is a loosely defined term used to describe a number of varieties of Homo, as opposed to anatomically modern humans , in the period beginning 500,000 years ago....
lineage such as the Neanderthals. It supports the idea that modern humans could have benefited by acquiring adaptive alleles evolved by our Neanderthal relatives - in this case, microcephalin
Microcephalin
Microcephalin is one of six genes causing primary microcephaly when non-functional mutations exist in the homozygous state...
, an adaptive allele associated with brain development. Microcephalin (MCPH1) regulates brain size, and has evolved under strong positive selection in the human evolutionary lineage. One genetic variant of Microcephalin, which arose about 37,000 years ago, increased its frequency in modern humans too rapidly to be compatible with neutral
Neutral theory of molecular evolution
The neutral theory of molecular evolution states that the vast majority of evolutionary changes at the molecular level are caused by random drift of selectively neutral mutants . The theory was introduced by Motoo Kimura in the late 1960s and early 1970s...
genetic drift
Genetic drift
Genetic drift or allelic drift is the change in the frequency of a gene variant in a population due to random sampling.The alleles in the offspring are a sample of those in the parents, and chance has a role in determining whether a given individual survives and reproduces...
. As anatomically modern humans emerged from Africa and spread across the globe, the “indigenous” Homo populations they encountered had already inhabited their respective regions for long periods of time and might have been better adapted to the local environments than the colonizers. It follows that modern humans, although probably superior in their own way, could have benefited from adaptive alleles gained by interbreeding with the populations they replaced, as appears to be the case for the brain size-determining gene microcephalin.
Agriculture
Farming, which, the authors note, produces 10 to 100 times more calories per acre than foraging, carried this trend further. Over the period from 10,000 BC to AD 1, the world population increased about a hundredfold - estimates range from 40 to 170 times. An accelerated rate of evolution is a direct result of the larger human population. More people will have more mutationMutation
In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...
s, thereby increasing opportunity for evolutionary change under natural selection. The spread of rapidly expanding populations eventually outpaced the spread of favourable mutations under selection in those populations, so for the first time in human history favourable mutations could not fully disperse throughout the human species. In addition, of course, selection pressures changed once farming was adopted, favouring distinctive adaptations in different geographic areas.
Farming, rather than just reduced sunlight, may have helped trigger pale skin in Europeans. In a 2007 study, almost all Africans and East Asians have one allele of the SLC24A5
SLC24A5
Sodium/potassium/calcium exchanger 5 also known as solute carrier family 24 member 5 is a protein that in humans is encoded by the SLC24A5 gene that has a major influence on natural skin colour variation. The NCKX5 protein is a member of the potassium-dependent sodium/calcium exchanger family...
gene, whereas 98% of the Europeans studied had the other. These data suggest that a selective sweep
Selective sweep
A selective sweep is the reduction or elimination of variation among the nucleotides in neighboring DNA of a mutation as the result of recent and strong positive natural selection....
occurred as recently as 5,300 to 6,000 years ago, replacing darker skins with light skins at astonishing speed. It implies that Europeans had been dark-skinned for tens of thousands of years. Several decades ago, Stanford's Cavalli-Sforza
Luigi Luca Cavalli-Sforza
Luigi Luca Cavalli-Sforza is an Italian population geneticist born in Genoa, who has been a professor at Stanford University since 1970 .-Books:...
had argued that European hunter-gatherers, herders and fishers could have survived from the vitamin D content of their diet, alone. Only when farming took hold did Europeans - replacing meat and fish with grain
Food grain
thumb|150px|Barleythumb|150px|LentilGrains are small, hard, dry seeds harvested for human food or animal feed Agronomists also call the plants producing such seeds grains or grain crops....
- need to absorb more sunlight to produce the vitamin in their skin. Other writers, including Darwin
Charles Darwin
Charles Robert Darwin FRS was an English naturalist. He established that all species of life have descended over time from common ancestry, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection.He published his theory...
, Miller
Geoffrey Miller (evolutionary psychologist)
Geoffrey F. Miller , Associate Professor of Psychology at the University of New Mexico, is an American evolutionary psychologist.Miller is a 1987 graduate of Columbia University, where he earned a B.A. in biology and psychology. He received his PhD in cognitive psychology from Stanford University...
, and Dawkins
Richard Dawkins
Clinton Richard Dawkins, FRS, FRSL , known as Richard Dawkins, is a British ethologist, evolutionary biologist and author...
, have proposed that skin colour changes were driven by sexual selection
Sexual selection
Sexual selection, a concept introduced by Charles Darwin in his 1859 book On the Origin of Species, is a significant element of his theory of natural selection...
. Cochran and Harpending reject the sexual selection idea when used to imply that race is no more than skin deep ("perhaps little more than a fad"), pointing out that experts can easily determine race from skeletal evidence alone.
Gene Flow
About halfway through the book, Cochran and Harpending pause to consider two different ways of looking at the information found in gene variants. Commonly they are seen merely as markersGenetic marker
A genetic marker is a gene or DNA sequence with a known location on a chromosome that can be used to identify cells, individuals or species. It can be described as a variation that can be observed...
of human migration, ignoring their functions. The authors support such research, but argue for a more complete understanding of the geographic distributions of genes. Where the usual geographical analysis treats the distribution of genes as an effect of history, in the authors' view, the genes themselves are a major cause: Two variants in the same gene do not necessarily have the same effect, and their relative, selective benefits will control the spread of genes through populations in both space and time.
Expansions
From that platform the authors discuss ideas that range from the possible origins of the ArthurianKing Arthur
King Arthur is a legendary British leader of the late 5th and early 6th centuries, who, according to Medieval histories and romances, led the defence of Britain against Saxon invaders in the early 6th century. The details of Arthur's story are mainly composed of folklore and literary invention, and...
legend in Britain to the Spanish colonization of the Americas
Spanish colonization of the Americas
Colonial expansion under the Spanish Empire was initiated by the Spanish conquistadores and developed by the Monarchy of Spain through its administrators and missionaries. The motivations for colonial expansion were trade and the spread of the Christian faith through indigenous conversions...
. Others have attempted this, for example in Jared Diamond’s Guns, Germs, and Steel
Guns, Germs, and Steel
Guns, Germs, and Steel: The Fates of Human Societies is a 1997 book by Jared Diamond, professor of geography and physiology at the University of California, Los Angeles . In 1998 it won the Pulitzer Prize for general non-fiction and the Aventis Prize for Best Science Book...
. But, according to Kelleher, Cochran and Harpending go one better than Diamond. Where he was content with environmental determinism
Environmental determinism
Environmental determinism, also known as climatic determinism or geographical determinism, is the view that the physical environment, rather than social conditions, determines culture...
, opposing the roles of human biology and population differences, Cochran and Harpending embrace them both. Their discussions of gene flow becomes the core of an argument for biology as central to history, and the backdrop for the book’s two major hypotheses.
The first seeks to resolve a longstanding debate in historical linguistics
Historical linguistics
Historical linguistics is the study of language change. It has five main concerns:* to describe and account for observed changes in particular languages...
by making a case for the Kurgan hypothesis
Kurgan hypothesis
The Kurgan hypothesis is one of the proposals about early Indo-European origins, which postulates that the people of an archaeological "Kurgan culture" in the Pontic steppe were the most likely speakers of the Proto-Indo-European language...
on the origins of the Indo-European language group
Proto-Indo-European Urheimat hypotheses
The Proto-Indo-European Urheimat hypotheses are designed to explain the origins of the Proto-Indo-European language and the people. The identity of the Proto-Indo-Europeans has been a recurring topic in Indo-European studies since the 19th century. Many hypotheses for an Urheimat have been...
. The Kurgan theory holds that Indo-European speakers came from lands between the Black
Black Sea
The Black Sea is bounded by Europe, Anatolia and the Caucasus and is ultimately connected to the Atlantic Ocean via the Mediterranean and the Aegean seas and various straits. The Bosphorus strait connects it to the Sea of Marmara, and the strait of the Dardanelles connects that sea to the Aegean...
and Caspian
Caspian Sea
The Caspian Sea is the largest enclosed body of water on Earth by area, variously classed as the world's largest lake or a full-fledged sea. The sea has a surface area of and a volume of...
seas before spreading their language by conquest. The authors suggest that dairy farming and a complementary adaptation - the ability to digest lactose in adulthood - lie behind their conquests. With a walking food source, the milk-drinking warriors defeated their plant-growing neighbours. Drinking milk, from cows, horses, or camels, is a behavior shared by many of history’s greatest conquering peoples, whether Kurgans, Scythians, Arabs, or Mongols
Mongols
Mongols ) are a Central-East Asian ethnic group that lives mainly in the countries of Mongolia, China, and Russia. In China, ethnic Mongols can be found mainly in the central north region of China such as Inner Mongolia...
. Without continuing evolution, the ability to digest milk could never have arisen. In fact, it has done so several times, in different ways, in various places, and it has helped shape human history. Kelleher comments that the authors’ argument makes it difficult to imagine the language in which their book would have been written, were it not for the ability to digest milk.
Ashkenazi Jews
The second major argument, which takes up the final chapter, sets out to explain why Ashkenazi JewsAshkenazi Jews
Ashkenazi Jews, also known as Ashkenazic Jews or Ashkenazim , are the Jews descended from the medieval Jewish communities along the Rhine in Germany from Alsace in the south to the Rhineland in the north. Ashkenaz is the medieval Hebrew name for this region and thus for Germany...
have a mean
Mean
In statistics, mean has two related meanings:* the arithmetic mean .* the expected value of a random variable, which is also called the population mean....
IQ
Intelligence quotient
An intelligence quotient, or IQ, is a score derived from one of several different standardized tests designed to assess intelligence. When modern IQ tests are constructed, the mean score within an age group is set to 100 and the standard deviation to 15...
so much higher than that of the population in general. This argument had been published previously in an earlier paper that attracted wide media coverage, generating extensive criticism and praise. This final chapter prior to the book's conclusion has been described as a consistent, thorough, biological history — or perhaps, better, a consistent biological hypothesis of a specific history, and a falsifiable one to boot.
Reviews
Wolpoff believes that Cochran and Harpending ‘‘get it’’ when so many paleo-anthropologist specialists don’t seem to: the significance of Neandertal genetic contributions to the modern gene pool is found in the importance of the genes that persisted, not in their quantity.In Seed
Seed (magazine)
Seed is an online science magazine published by Seed Media Group. The magazine looks at big ideas in science, important issues at the intersection of science and society, and the people driving global science culture...
Magazine, T.J. Kelleher, describes this book as a manifesto for and example of a new kind of history, a biological history - and not just of the prehistoric era. Kelleher writes that, covering broad ground over human history and prehistory, the authors argue for the singular importance of genes in human history, not just as markers of it, but also as its makers.
In respect of Askenazi Jews, however, Kelleher feels that Cochran and Harpending’s impatience to get to the core of their argument drives them to quickly dismiss most of their critics — too quickly, given the long and rancorous debate in the United States about the genetic heritability of intelligence. It would have benefited the book to consider those criticisms at greater length.