The Origins of Native Americans: Evidence from Anthropological Genetics. Michael H. Crawford. Cambridge University Press, 1998. xv + 308 pp., includes author and subject indices. $64.95 (cloth). ISBN 0-521-59280-1.
Reviewed by David L. Browman, Department of Anthropology, Washington University, St. Louis, MO 63130-4899.
This book is a revised English translation of Crawfords 1992 Spanish language volume published for the 500th anniversary of Columbus journeys. The revised edition is still subsidized by the MAPFRE American Foundation of Madrid, Spain, but has some significant differences from the Spanish version. In this volume, Crawford eschews much of the osteological work, feeling that most publications are "strongly slanted towards osteology" (p . xiv) and instead elects to focus primarily upon the evidence from genetics. In addition, he has "personalized" (p. xiii) this new volume by emphasizing much of his own work. Thus much of the discussion focuses upon the Black Caribs and Tlaxcaltecans of Mesoamerica, and a selected group of Eskimo and Siberian groups in the Arctic. In spite of its more encompassing title, then, the book centers primarily on North America; Crawford recognizes this and frequently refers his readers to the volume by Francisco Salzano and Sidia M. Callegari-Jacques (1988) for coverage of South America.
In Chapter 1, Crawford reviews ideas from linguistics, archaeology, and biological anthropology for the origin and antiquity of humans in the New World. This chapter is basically unchanged from the earlier version, and thus somewhat out-of-date. In linguistics, for example, none of the new work of Johanna Nichols is mentioned. The archaeology relies on materials of 15 years ago, and does not include corrections and changes made in Siberian dating. Because osteology is downplayed, there is no discussion of the implications of recent finds such as Hourglass Cave, Buhl, Kennewick, Windover, etc. The antiquity of the first migration is placed at 35-40,000 years ago, based on mutation rate estimates for mtDNA haplotypes. This age estimate assumes no heteroplasmy, although some recent studies hypothesize rates might be as high as 10-20%; and also assumes that all differentiation represents genetic mutations which occurred only subsequent to the crossing of the Bering land bridge into the Americas.
Chapter 2 focuses on population size estimates of the New World in A.D. 1500. Crawford places the number at 44 million, proposing that 3/4 of the entire population was clustered in Mesoamerica and the Caribbean. He presents a surprisingly high estimate of 7 million for the Caribbean Islands, and a rather low estimate of only 3.5 million for the entire Inca empire (which was six times larger than the Aztec empire in spatial area in A.D. 1500). In the later part of the chapter, the evidence for New World infectious diseases is summarized. The third chapter continues the demography theme, discussing parameters of fertility, mortality, immigration, and emigration.
The subsequent trilogy of Chapters 4-6 is the real essence of the volume. It is here, in quasi "Annual Review" style, that Crawford lays out the information from human genetics that he wants to highlight in this volume. He recognizes genetic variations as the result of three factors: (a) the number and sizes of the first migratory populations; (b) the influence of various mechanisms of gene flow; and (c) the more recent impacts upon the Amerindians through epidemics, warfare and slavery. He examines the implications of (a) in Chapter 4, of (b) in Chapters 5 and 6, and of (c) in Chapter 7.
In Chapter 4 Crawford deals with blood group, serum-protein, red cell protein, histocompatibility and DNA polymorphisms, and discusses their implications with respect to the possible founding populations. Many researchers have attempted to employ genetic markers to identify the number and size of early migratory groups, essentially by assuming one can ignore or eliminate the contributions of (b) and (c) above. Crawford believes this may be possible because it appears that systems which display variable numbers of tandem repeats reveal more current or recent evolutionary history, whereas the variation in gene products are more conservative evolutionarily, and thus display the results of natural selection in more ancient time. On this basis, he argues that evidence from the suite of genetic markers he reviews indicate that the "founding populations must have been small, probably made up of extended lineages, and were not randomly constituted subsets of the ancestral groups", that is, the genetic patterning follows the fusion-fission model, although he does caution that "in these groups gene pools were highly subject to stochastic processes and past effects of selection might not be discernible to us."(p. 147)
Chapter 5 is devoted to the evaluation of population structure, admixture and gene flow over time. Employing particularly his data from the Black Caribs of Honduras, the Tlaxcaltecans of Mexico, the St. Lawrence Island Eskimos, and selected Siberian groups, he argues for significant correlations between genetics and geography, genetics and latitude, and genetics and language.
Chapter 6 reviews what he considers the significant components of morphological variation. He maintains that genetic studies are superior to morphological studies because: (i) there are major inter-observer variation errors in measurement in morphology, and (ii) ontogenetic changes have significant impacts on specific measurements. While Crawford does note that the "comparison of two independent research groups genetic characterizations of the same population one year apart reveals that even under optimal conditions some differences in gene frequencies and detection of a few specific alleles will be seen" (p. 92), he argues that in contrast to the morphological inter-observer errors, these inter-observer differences in genetic variations have little impact upon measurement of population parameters. This chapter gives a summary of anthropometric, dermatoglyphic, dentition, and skin color studies. Here he also concludes that the traits are ecosensitive; that is, he sees significant correlation between anthropometrics and geography, and dermatoglyphics and geography, which he finds not surprising, as much of the variation in polygenetic traits expressed in morphological measures is believed to be a consequence of gene-environment interaction.
In Chapter 7 he turns to assessing the impact of isolation (reservations), hybridization and disease on the surviving First Nations populations. Discussion of implication of issues such as the thrifty gene hypothesis and its relationship to late-onset non-insulin-dependent diabetes mellitus, the effect of conquest and epidemics, the impact of socioeconomic factors, and other medical and evolutionary costs of survivorship are reviewed. The resulting evidence clearly shows that the Amerindian population has passed through a tight selective "bottleneck"; this coupled with the massive gene flow and hybridization resulting from European conquest "has forever altered the genetics of the surviving groups, thus complicating any attempts at reconstructing the pre-Columbian genetic structure" (p.261); any genetic reconstruction of the earliest migrants will necessarily be susceptible to challenge because of these two issues.
As the subtitle suggests, this is a solid review of the evidence from anthropological genetics, especially for the First Nations populations of North America. Morphological studies are explicitly less considered. Despite the main title, Crawford is less concerned with the current debates on origins, but more interested in providing us with a comprehensive synopsis of the advances made in studying variations of human genetics of First Nations, and in this he has succeeded admirably.
Crawford, Michael F. 1992 Antropologia Biologica de los Indios Americanos. Madrid: Editorial MAPFRE.
Salzano, Francisco, and Sidia M. Callegari-Jacques. 1988. South American Indians: A Case Study in Evolution. Oxford: Clarendon Press.