INTRODUCTION

The Siberian populations that expanded into the New World some 30 000–40 000 years BP grew numerically, diffused geographically, and eventually reached Tierra del Fuego at the tip of South America. The total number of descendants of the original migrants is a function of the ecological factors in the diverse regions of the Americas and the extractive efficiency of the cultures of residents of these regions. For example, the population densities of hunting and gathering societies were much lower than those of the agriculturalists. As a result, the population densities must have differed in the various regions of the New World, with the highest densities occurring in the Highlands of Central America and Peru, where intensive agriculture could maintain populations of large size. In contrast, the Sonoran or Californian deserts could not have sustained populations of hunters and gatherers with densities greater than a few individuals per square kilometer.

How many Amerindians and Eskimos did inhabit the New World in 1492? Estimates of the size of the population have varied from Dobyns'(1966) 90–112.5 million to Kroeber's (1939) 8.4 million. Dobyns based his numerical estimates upon the reconstructions of population sizes by region when they were at their lowest and then corrected these figures by a 20 : 1 or 25 : 1 depopulation ratio. Kroeber, on the other hand, utilized a tribe-by-tribe ‘dead reckoning’ method (developed by Mooney in 1910) gradually building up totals for each geographical region.

METHODS OF ESTIMATION

Douglas Ubelaker (1988) has summarized the various approaches used to estimate the size of the aboriginal population of North America.

INTRODUCTION

In this final chapter the biomedical effects of acculturation and the accompanying changes in lifestyle of the Amerindians who survived the depopulation are considered. The interaction of culture change with the underlying genetics of native people provides a unique opportunity to assess and better understand the mechanisms involved in the etiology of complex diseases. In addition, research into unique Native American responses to various degenerative diseases may shed some light on the mechanisms of interactions between genetic and various environmental factors. The evolutionary consequences of increased genetic admixture between Amerindian populations (resulting from tribes with separate ethnohistories and geographic isolation being forced to coexist in newly created reservations) are also considered in this chapter. The massive infusion of genes from Africans and Europeans into Native American gene pool has undoubtedly altered the risks of diseases in admixed families.

The occupation of the Americas by peoples of Siberian ancestry for possibly 30 000–40 000 years was dramatically disrupted within the past 25 generations (500 years) by a violent collision between Old and New World cultures (see Crawford, 1992a, b). The consequences of this confrontation and the conquest that followed have been, and still are, devastating to the numerical balance that had existed between the environment and the Amerindian populations (see chapter 2). From a total Indian population perhaps approaching 44 million persons at contact, conquest and its numerous sequelae hammered the population down to fewer than 10 million at the nadir. Only recently has the surviving Amerindian population recovered and in some regions of the Americas, such as the Valley of Tlaxcala, begun to increase and perhaps even surpass its pre-Columbian levels (see chapter 2, Fig. 13).

INTRODUCTION

Before we delve into the genetic variation observed in the contemporary native populations of the Americas, some causes of this phenomenon must be explored. It is highly unlikely that the patterns of variation observed in today's Amerindian populations resemble those that existed in pre-Columbian times. The present patterns of observed genetic variation are a result of a melange of factors. These are:

(1) The numbers and sizes of migrations (expansions) across Beringia. As discussed in chapter 1, there is considerable controversy as to the number of migrations or demic expansions, from Siberia to Alaska, which added genes to the populations of the Americas. What proportion of the genetic variation is due to the heterogeneity of the founding populations and what proportion is made in America? If the ancestral groups were small in size, then stochastic processes would have contributed much to the observed variation, especially if these groups were large in number.

(2) The continuation of gene flow into the Americas after the last glaciation. My fieldwork with the Eskimos of St. Lawrence Island and Wales, Alaska, revealed that despite the severest impediments to gene flow, such as political borders and hostile troop concentrations, contact between the Old and New Worlds continued. Up to World War II, Alaskan Eskimos crossed the winter ice pack into Siberia to obtain wives. It is my contention that social contacts persisted in the Norton Sound region between the Eskimo groups of both sides of the Bering Strait and that complete reproductive isolation between the Old and New Worlds is a myth.

INTRODUCTION

The demography of human populations consists in part of their quantitative characteristics, including age/sex structure, size, fertility, mortality and migration patterns. The interrelations between fertility, mortality, emigration and immigration rates permit predictions of the numerical changes that a population may undergo during specific periods. For example, in reproductively closed populations such as species, the relative magnitudes of fertility versus mortality alone determine the size of the population. However, in most human populations it is the interaction of fertility and immigration versus mortality and emigration that determine the numerical trends in population size. This chapter considers the demographic structure of Amerindian populations both before European Contact and today. Given the broad scope of this volume, encompassing all of the indigenous peoples of the Americas and a heterogenous melange of populations of different sizes and subsistence patterns, it is not possible to reconstruct the demographic characteristics population by population. Instead, I shall endeavor to distill some of the common denominators of Amerindian populations. In addition, I shall present some examples that are particularly informative about the processes acting upon the demographic structures of these populations.

DEMOGRAPHY OF PRE-COLUMBIAN AMERINDIANS

The demographic characteristics of the populations of the Americas, prior to European contact, are often estimated from small amounts of information. There are no censuses or vital registers, both sources of data traditionally utilized by demographers. Instead, archeologists and biological anthropologists reconstruct the dynamics of prehistoric populations through the use of cultural artifacts, skeletal remains and the extrapolation of models derived from contemporary populations.

INTRODUCTION

The history of physical (also known as biological) anthropology is intimately bound to the study of morphological traits and their uses in attempts to classify human races. Early physical anthropologists, such as F. Boas and A. Hooton, devoted much of their research energy to the collection of anthropometric data (body measurements) and anthroposcopic data (results of subjective grading of morphological characteristics that cannot be concisely measured) for the characterization of human races. Both the anthropometric and anthroposcopic traits have two distinct disadvantages in the study of human populations: (1) technical error (interobserver variation), which can be reduced to some degree in measurements and observations; and (2) ontogenetic changes in specific measurements, such as girth, height and weight. It is this ontological impermanence of measurements under changing environmental conditions that render anthropometries unsuitable for tracing long-term genetic relationships between the races. These problems associated with morphological traits are the major reasons that there was a ‘stampede’ by scientists to use the genetically based blood groups for evolutionary studies when methods for rapidly identifying these traits became available. The blood phenotypes remain unchanged throughout the life of the individual. Although there can be laboratory error associated with blood typing, this problem can be overcome by using independent determinations from two laboratories (Osborne, 1958). By the 1950s and 1960s, many American biological anthropologists had stopped utilizing anthropometric measurements in their studies of human population relationships.

The realization of the ecosensitivity (environmental responsiveness) of morphological traits shifted the use of these measurements from studies of race to those of processes of genetic–environmental interaction (Kaplan, 1954).

Like the histories – both biological and cultural – of the native peoples to whom this book is dedicated, the making of this book is a story of expansion and confrontation, admixture and adaptation, though, fortunately, on a gentler plain: the plain of science. My interests in the human biology of New World populations were originally stimulated by my association with the late Marshall T. Newman at the University of Washington. Bud, as he was known to his friends, joined the anthropology faculty there in 1966, as I was completing my final year of graduate studies. Although I never received any formal instruction from him, I did sit in on a number of his seminars, and, over the course of that year, we discussed many aspects of Amerindian biology.

The idea for this particular volume came into existence more than twenty years ago, at a dinner at Bud's house in Seattle. Although we had shared many interests and ideas, Bud and I had never published anything together, and, that night, we decided that we should begin work on a volume concerning the biology of the native populations of the New World. Unfortunately, this project never came to fruition, pushed to the back burner by the protracted illness and eventual death of Bud's wife, Judy, and last year by Bud's death.

The next stage in the evolution of this volume occured six years ago, when I was approached by the MAPFRE Foundation to write a volume on the physical anthropology of American Indians.