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
Before the Dawn: Recovering the Lost History of Our Ancestors Page 38