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Before the Dawn: Recovering the Lost History of Our Ancestors

Page 38

by Nicholas Wade


  363 The test by Pritchard and his colleagues was based on the fact that a beneficial mutation is inherited in a large block of DNA, which will carry its own signature set of DNA changes. If the gene with the good mutation spreads rapidly, along with its block, the DNA in that region of the chromosome will become less diverse in the population as a whole because so many people now carry the same sequence of DNA units at that location.Pritchard’s test measures the difference in diversity between those who carry a new version of a gene and those who do not. Lesser diversity in a population is taken as a sign of selection. The difference in diversity disappears as the gene becomes universal, because increasing numbers of people carry the new variant. Thus the test picks up only new gene variants on their way to becoming universal, i.e., recently selected genes.

  Pritchard looked for blocks with selected genes in data gathered by the Hap Map project from Africans (specifically, the Yoruba people of Nigeria), East Asians, and Europeans. The time of the selective pressure is about 10,800 years ago for the African genes and 6,600 for the East Asian and European genes.

  As shown in the figure on page 298, 206 selected genetic regions were identified in Africans, 185 in East Asians, and 188 in Europeans. The fact that the selected genes do not overlap very much indicates that each population evolved independently. The selected genes shared by two races may have arisen by migration or be instances of independent evolution.

  The genes under selection clustered in specific categories. Some of the strongest signals of selection were for 4 genes for skin color, found to be under selection in Europeans but not in Asians. Another category of selected genes was in those for skeletal development (possibly reflecting the gracilization of human populations). Other selection categories were genes for fertility, for taste and smell, and genes involved in the metabolism of foodstuffs. The latter two groups may reflect the sharp changes in diet that followed the Neolithic revolution. Benjamin Voight, Sridhar Kudaravalli, Xiao quan Wen, and Jonathan K. Pritchard, “A Map of Recent Positive Selection in the Human Genome,” PloS Biology, 4: 446-458 (2006).

  364 A remarkable 20 percent of men in northwestern Ireland carry a particular set of mutations on their Y chromosome, known as the Irish modal haplotype. Many have surnames that are associated with the Ui Neill, a group of dynasties that claimed the high kingship of Ireland and ruled the northwest and other parts of Ireland from about A.D. 600 to 900. Ui Neill means “descendants of Niall.” Historians have tended to regard the Ui Neill as a political construct and its patriarch, Niall of the Nine Hostages, as a probably legendary figure. The genetic evidence provides striking evidence that Niall really existed, a finding as surprising as if the legend of King Arthur turned out to be solid his-tory.

  FIGURE 9.1

  Genes that have undergone recent evolutionary change in the genomes of East Asians (ASN), Europeans (CEU), and Africans (YRI).

  The Irish modal haplotype, the signature of descent from Niall, is most common in northwestern Ireland but is also found in the Irish diaspora, being carried by no less than 2 percent of New Yorkers of European descent. Evidently one should listen less skeptically to Irishmen who declare the blood of Irish kings runs in their veins. Laoise T. Moore et al., “A Y-Chromosome Signature of Hegemony in Gaelic Ireland,” American Journal of Human Genetics, 78: 334-338 (2006).

  ACKNOWLEDGMENTS

  This book grew out of conversations with the many scientists whom I interviewed in the course of writing articles about the genetics of human origins for the New York Times. I am most grateful to them for sharing their knowledge and insights.

  I thank Peter Matson, of Sterling Lord Literistic, for shaping the idea of the book, and Emily Loose, its editor at Penguin Press, for shaping its structure. I am also grateful to the New York Times for giving me leave to write it.

  Henry Harpending, an anthropologist at the University of Utah, Richard Klein, a paleoanthropologist at Stanford University, and Kari Stefansson of DeCode Genetics in Iceland, were kind enough to read parts of the manuscript. I thank them for their helpful emendations; they bear no responsibility for errors that may remain. I am indebted to friends who read the book in draft and saved me from many lapses, including Nancy Sterngold of Los Angeles, Jeremy J. Stone of Catalytic Diplomacy, Richard L. Tapper of the London School of Oriental and African Studies, and my wife, Mary V. Wade.

  I thank the Velasco brothers of 5W Infographic for drawing many of the graphics and Steven E. Duenes of the New York Times for graphical advice.

  CREDITS

  FIGURE 2.1. Family tree of humans and other great apes. Adapted from M. A. Jobling et al., Human Evolutionary Genetics, Garland Publishing 2004, p. 222. Source: Pascal Gagneux et al., “Mitochondrial Sequences Show Diverse Evolutionary Histories of African Hominoids,” Proceedings of the National Academy of Sciences, 96, 5077-5082, 1999, © 1999, National Academy of Sciences, U.S.A.

  FIGURE 2.2. Evolution of human stone tool kits. From Richard Klein, The Human Career, University of Chicago Press, 2nd edition 1999, p. 576.

  FIGURE 2.3. The three human species of 50,000 years ago. Illustration by 5W Infographic.

  FIGURE 4.1. The universal human Y chromosome. Illustration by 5W Infographic.

  FIGURE 4.2. The Y chromosome family tree and its geographical distribution. Illustration by 5W Infographic.

  FIGURE 4.3. Mitochondrial DNA family tree and its geographical distribution. Illustration by 5W Infographic.

  FIGURE 5.1. The route from Africa to the former continent of Sahul. Illustration by 5W Infographic.

  FIGURE 5.2. The arrival of modern humans in Europe. From Paul Mellars, “The Impossible Coincidence. A Single-Species Model for the Origins of Modern Human Behavior in Europe,” Evolutionary Anthropology 14, 12-27, 2005. © Paul Mellars 2005. Reprinted with permission of Wiley-Liss, a subsidiary of John Wiley & Sons, Inc.

  FIGURE 6.1. The roller coaster of climate change in the Upper Paleolithic. Copyright Randall White, New York University.

  FIGURE 6.2. The forced evacuation of Europe and Asia. Illustration by 5W Infographic.

  FIGURE 7.1. The homeland of the Natufians, the first foragers to settle. From Ofer Bar-Josef, “On the Nature of Transitions: The Middle to Upper Palaeolithic and the Neolithic Revolution,” Cambridge Archaeological Journal, 8:2, 1998, Cambridge University Press.

  FIGURE 9.1 Genes that have undergone recent evolutionary change in the genomes of East Asians (ASN), Europeans (CEU), and Africans (YRI).

  FIGURE 10.1. Large language families may have arisen through farming. Illustration by 5W Infographic, adapted with permission from Jared Diamond and Peter Bellwood, “Farmers and Their Languages: The First Expansions,” Science 300, 597-603, 2003, © 2003 AAAS.

  FIGURE 10.2. A geneticist’s tree of the Indo-European language family. Illustration by Quentin Atkinson, University of Auckland, New Zealand.

  FIGURE 10.3. The world’s language superfamilies. From Merritt Ruhlen, A Guide to the World’s Languages, p. 284-285. Stanford University Press 1991, © 1987 by the Board and Trustees of the Leland Stanford Jr. University.

  FIGURE 10.4. The Afroasiatic language family. From Merritt Ruhlen, A Guide to the World’s Languages, p. 284-285. Stanford University Press 1991, © 1987 by the Board and Trustees of the Leland Stanford Jr. University.

  FIGURE 10.5. The distribution of Eurasiatic. From Joseph H. Greenberg, Indo-European and Its Closest Relatives, Stanford University Press, 2002, © 2000 by the Board and Trustees of the Leland Stanford Jr. University.

  FIGURE 11.1. Thomas Jefferson’s family with Sally Hemings. From M. A. Jobling et al., Human Evolutionary Genetics, Garland Publishing 2004, p. 492.

  INDEX

  Page numbers in italics refer to figure captions.

  Acheulean tools

  Adam, genetic

  Africa

  ancestral humans’ exodus from

  ancestral humans’ home in

  ape society transformed into human society in

  archaic humans’ mov
e out of

  climate in

  date of modern humans’ exodus from

  gracilization in

  lactose tolerance in

  languages in

  melanocortin receptor gene in

  racial origins in

  route to Sahul from

  African Americans

  aggressiveness

  domestication and

  and privatization of sex

  socially approved

  agriculture

  language and

  AIDS

  Akkermans, Peter

  Alaska

  alleles

  altruism

  reciprocal

  American Anthropological Association

  American Indians (Native Americans)

  cannibalism among

  dogs and

  languages spoken by

  as race

  warfare and

  American Sociological Association

  Americas

  race and

  Amhara people

  Ammerman, Albert

  Anasazi Indians

  ancestral human population

  Adam in

  African exodus of

  African homeland of

  current ancient populations and

  Eve in

  fragmentation of; see also race

  great civilizations and

  language of

  modern behavior in

  portrait of

  religion among

  San people as similar to

  size of

  time period of

  Universal People concept and

  Ancestry Informative Markers

  Andaman Islanders

  anthropologists

  cannibalism and

  paleoanthropologists

  social

  warfare and

  apes:

  chimpanzees, see chimpanzees

  evolution to humans

  family tree of humans and

  gorillas, see gorillas

  human/chimp split

  joint human-chimp ancestor

  language and

  orangutans

  social behaviors among

  walking

  Arabia

  archaeologists

  Australian settlement and

  cannibalism and

  genetics and

  intrusions and

  language and

  settlement and

  warfare and

  archaic humans

  Africa left by

  Homo erectus, see Homo erectus

  Neanderthals, see Neanderthals

  tools used by

  archaic states

  Arens, William

  art

  cave

  language and

  Asia

  brain genes and

  East-West cultural differences and

  gracilization in

  racial origins in

  teeth of people in

  Upper Paleolithic in

  ASPM gene

  Atkinson, Quentin

  ATP

  Aurignacians

  Australia

  Damin language in

  date of settlement of

  languages in

  teeth of people in

  tribes in

  australopithecines

  brain size of

  robust

  Aztecs

  Bab al-Mandab (Gate of Grief)

  baboons

  communication among

  Baker, Robin

  Barger, Herbert

  Bar-Yosef, Ofer

  bats

  Bayesian Markov chain Monte Carlo method

  beads

  beauty

  Bedouin

  behaviorally modern humans

  behaviors

  sexual, see sexual behaviors

  social, see sociality, social behaviors

  of Universal People

  Beja-Pereira, Albano

  Bellwood, Peter

  Belyaev, Dmitri K.

  Bender, Lionel

  Beringia, Bering land bridge

  Bickerton, Derek

  BiDil

  bipedalism

  birds, fidelity in

  Bloom, Paul

  Blust, Robert

  boats and navigation

  Bodmer, Walter

  Bølling-Allerød Interstadial

  bonobos

  chimpanzees and

  in family tree

  pedomorphic change among

  sexual behaviors of

  social behaviors of

  tools and

  Borneo

  Boster, James

  bows and arrows

  brain:

  diet and

  evolution of

  genes and

  brain size

  of australopithecines

  of chimpanzees

  of Floresians

  of Homo ergaster

  of Homo habilis

  increase in

  of infants

  of modern humans

  of Neanderthals

  Britain

  mad cow disease in

  Brooks, Alison S.

  Brown, Donald

  Bulgaria

  Burch, Ernest

  burial practices

  Buss, David

  Callender, James T.

  cancer

  cannibalism

  Caribbean

  Carr family

  cattle

  Caucasians

  Cavalli-Sforza, Luca

  Celts

  cereals

  Chagnon, Napoleon

  Chile

  chimpanzees

  altruism among

  battles of

  bonobos and

  brain volume of

  in family tree

  female

  genome of

  hair of

  human body language and

  human line of descent split from

  joint human-chimp ancestor

  knuckle-walking of

  language and

  male

  sexual behaviors of

  skin color of

  social behaviors of

  sperm production in

  tools used by

  warfare among

  China

  East-West cultural differences and

  Manchu rulers in

  Chomsky, Noam

  Universal Grammar of

  chromosomes

  genetic engineering and

  and large blocks of DNA

  X

  Y, see Y chromosome

  cities, first

  civilizations, great

  climate

  in Africa

  agriculture and

  cold, adaptation to

  global

  language and

 

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