Genetics and the Search for Modern Human Origins

by Relethford, John H.

• ISBN13: 9780471384137
• ISBN10: 0471384135
• Edition: 1st
• Format: Hardcover
• Copyright: 2001-04-20
• Publisher: Wiley-Liss

Summary

A major debate in anthropology concerns the relationship between anatomically modern humans and earlier "archaic" humans including the Neandertals. What was the origin of modern humans? Did we arise as a new species in Africa 200,000 years ago and then replace archaic human populations outside of Africa, or are our origins part of a single evolving lineage extending back over the past two million years? In addition to fossil and archaeological evidence, anthropologists have increasingly turned to using genetic data on living populations to address this question. Patterns of genetic variation within and between living human populations are felt to contain clues as to our species' evolutionary history, and provide a reflection of the past. This book reviews the modern human origins debate focusing on the genetic evidence relating to our origins, including genetic variation in living humans and recent discoveries of ancient DNA from fossil specimens. Following a brief introduction to the problem and a review of evolutionary genetics, the book focuses on gene trees and the search for a common ancestor, genetic diversity within populations, genetic distances between populations, the use of genetic data to reconstruct ancient demography, and Neandertal DNA. The main point of the text is that although the genetic data are often compatible with a replacement model, they are also compatible with some multiregional models. The concluding chapter makes the case that modern human origins are mostly, but not exclusively, out of Africa.

Author Biography

Dr. Relethford completed his BA, MA, and Ph.D. degrees in anthropology at the State University of New York at Albany. He worked as a postdoctoral research scientist at the Southwest Foundation for Biomedical Research in San Antonio before joining the faculty at the State University of New York at Oneonta. He is currently Distinguished Teaching Professor and Chair of the Department of Anthropology at SUNY-Oneonta, and is a recipient of the SUNY Chancellor's Award for Excellence in Teaching. He has published numerous articles on human population genetics, human biological diversity, and modern human origins, and is the author of an introductory textbook in biological anthropology, The Human Species, 4th Edition.

Table of Contents

Reflections of the Past	1	(9)
The Genetic History of the Human Species	3	(3)
The Organization of this Book	6	(4)
Evolution and Genetic History	10	(31)
The Genetic Code	11	(1)
The Process of Inheritance	12	(3)
Dominant, Recessive, and Codominant Alleles	14	(1)
Inheritance of Chromosomes	15	(1)
Measures of Genetic Variation	15	(5)
Red Blood Cell Blood Polymorphisms	16	(1)
DNA Markers	17	(2)
Mitochondrial DNA	19	(1)
The Y Chromosome	19	(1)
Complex Phenotypic Traits	20	(1)
How Does Evolution Work?	20	(12)
Mutation	21	(1)
Natural Selection	22	(2)
Genetic Drift	24	(4)
Gene Flow	28	(1)
Interaction of the Evolutionary Forces	28	(1)
Microevolution and Macroevolution	29	(3)
Genetics and History---Two Examples	32	(7)
The Population History of Ireland	32	(3)
The Ape-Human Split	35	(3)
Different Approaches to Population History	38	(1)
Summary	39	(2)
The Modern Human Origins Debate	41	(26)
Geologic Time	42	(1)
Early Hominid Evolution	43	(2)
Evolution of the Genus Homo	45	(9)
Early Humans---Homo erectus	46	(2)
``Archaic'' Humans	48	(1)
``Modern'' Humans	49	(2)
Lumpers and Splitters	51	(3)
Models of Modern Human Origins	54	(12)
The Mode of the Transition---Replacement or Multiregional Evolution?	55	(6)
The Location and Timing of the Transition---Africa or Worldwide?	61	(1)
Evolutionary Models	62	(4)
Summary	66	(1)
In Search of Our Common Ancestor	67	(27)
``Mitochondrial Eve''	68	(15)
Analyzing Mitochondrial DNA	68	(7)
The Analyses	75	(4)
The Debates---Where Did Eve Live?	79	(3)
The Debates---When Did Eve Live?	82	(1)
Coalescent Theory---When Did the Common Ancestor Live?	83	(6)
Estimates of Coalescent Dates from Mitochondrial DNA	85	(2)
Estimates of Coalescent Dates from Other Genes	87	(1)
Coalescent Dates and Population Size	88	(1)
Geography and Gene Trees---Where Did Our Ancestors Live?	89	(2)
Summary	91	(2)
Postscript	93	(1)
Genetic Diversity and Recent Human Evolution	94	(25)
Genetic Diversity and Evolution	95	(2)
Measuring Genetic Diversity	97	(4)
The Geographic Distribution of Human Genetic Diversity	101	(3)
Evolutionary Interpretations of African Genetic Diversity	104	(13)
A Recent African Origin of Our Species?	104	(6)
Regional Variation in Population Size?	110	(7)
Summary	117	(2)
Genetic Differences Between Human Populations	119	(26)
Genetic Distance and Evolution	119	(3)
Levels of Genetic Differentiation	122	(5)
The Pattern of Genetic Distances Between Populations	127	(1)
Evolutionary Interpretations	128	(15)
Do the Genetic Distances Reflect Phylogenetic Branching?	130	(2)
Do the Genetic Distances Reflect Differences in Gene Flow?	132	(5)
The Need to Consider Regional Differences in Population Size	137	(4)
Estimating Ancient Migration	141	(2)
Summary	143	(2)
How Many Ancestors?	145	(33)
Different Concepts of Population Size	146	(3)
Estimating Ancient Population Size	149	(5)
Ecological Estimates of Census Size	150	(1)
Genetic Estimates of Species Effective Size	151	(3)
A Pleistocene Population Explosion?	154	(14)
Gene Trees and Population Expansion	154	(2)
Mismatch Distributions and Frequency Spectra	156	(3)
Evidence of Expansion from Microsatellite DNA	159	(2)
Estimating the Time of the Expansion	161	(3)
What Happened Before the Expansion?	164	(4)
Evolutionary Interpretations	168	(8)
Evidence of Speciation and Replacement?	168	(3)
Extinction and Recolonization of Local Populations?	171	(5)
Summary	176	(2)
Neandertal DNA	178	(16)
Studying Ancient DNA	178	(1)
Discovery of Neandertal DNA	179	(2)
The First Neandertal DNA Sequence (Feldhofer)	179	(1)
The Second Neandertal DNA Sequence (Mezmaiskaya)	180	(1)
Evolutionary Interpretations	181	(9)
Variation within Neandertals	182	(1)
Were Neandertals a Separate Species?	183	(3)
Regional Affinities of Neandertal DNA	186	(4)
Were Neandertals a Different Subspecies?	190	(1)
Summary	190	(2)
Postscript	192	(2)
Putting the Pieces Together	194	(18)
Summary of the Genetic Evidence	195	(2)
The Fossil Record---A Population Geneticist's View	197	(8)
The Distribution of Archaic and Modern Fossils	198	(1)
Similarity of Recent Moderns to Earlier Archaics and Moderns	199	(3)
Regional Continuity	202	(3)
``Mostly Out of Africa''	205	(5)
Issues and Future Directions	210	(2)
Chapter Notes	212	(20)
Bibliography	232	(14)
Index	246