Viewing the biotic world in all its diversity, we may find it hard to believe that there is anything that is common to all forms of life. Yet, beneath their obvious and enormous differences, the human, the housefly, the rose, and the amoeba are alike in a number of important ways.
To begin with, all living things share the same underlying structure. Every organism is composed of one or more cells, and all cells are composed of the same basic materials: water, minerals, and organic compounds, such as carbohydrates, fats, proteins, nucleotides, and their derivatives. In addition, the same basic ac- tivities go on within every organism. First, there is metabolism, which includes nutrition, respiration, and synthesis, on which the survival and well-being of the organism depend. Because of metabolism, all organisms depend on their environ- ment for food that can be converted to energy and for other vital resources. Sec- ond, most organisms are genetically programmed to respond to most external and internal stimuli in a self-preserving and self-serving manner.1 Third, every orga-
nism has a capacity for reproducing itself in substantially greater numbers than are needed for simple replacement if all offspring were to survive.
The explanation of these and other common characteristics among other- wise vastly dissimilar forms of life is that all life on our planet is descended from a common source and subject to the same common evolutionary forces. As George Gaylord Simpson (1951: 281) once wrote, “all living things are brothers in the very real, material sense that all have arisen from one source and been developed within the divergent intricacies of one process.”
The key to understanding biological evolution lies in the basic units of he- redity known as genes. Genes, as we have discovered in recent decades, are com- plex chemicals that are present in every cell of every organism, and they contain, in coded form, information that profoundly influences both morphology and behavior. Sometimes the influence of the genes is deterministic; other times it merely predisposes the organism to act or develop in certain ways, while provid- ing latitude for alternative courses of action or development.
From a functional standpoint, the gene pool of a population of organisms is
a vast storehouse of information that has been acquired over countless generations
through the trial-and-error process of mutation and natural selection, and the
1. Altruistic behavior also seems to be genetically programmed into some species, but even in these species it is often less frequently activated than self-preserving behavior and tends to be re- stricted to closely related individuals, as in maternal defense of immature offspring.
The Biological Foundations of Human Societies 35 population’s survival depends on it. Much of the information contained in the gene pool appears redundant, some of it irrelevant, and some even harmful, but this in no way diminishes the critical importance of the information system as a whole.2
As the process of natural selection implies, the genetic heritage of every species is influenced by its ancestors’ interaction with the various environments they encountered. The biophysical environment is the testing ground for every population and its genetic heritage. Reproductive success is generally considered the best measure of the fitness, or overall adaptation, of an organism.
Adaptation is an important concept in the biological sciences, but it is some- times used in ways that confuse more than clarify. Writers often fail to distinguish between long- and short-term adaptation. What is adaptive for a population or species in the long term is not always adaptive in the short term, and vice versa. For example, many species have adapted to their environments by becoming in- creasingly specialized, using an ever-more limited set of resources more and more effectively (Cooper and Lenski, 2000). In the short run, this can be highly adap- tive. In the long run, however, it can prove disastrous if environmental changes reduce or destroy the limited set of resources on which the population has become dependent. Should that happen, the entire population may be wiped out.
As this reminds us, adaptive change is always governed by immediate cir- cumstances and forces operative in the short run. If such change also proves ben- eficial in the long run, that is in some sense accidental and, in fact, the outcome of a succession of short-run processes. This is the essential insight that underlies Darwin’s important concept of natural selection. It is only the human observer with his or her concepts of time, change, and history who is tempted to think of genetic change in populations as though it were influenced by long-term consid- erations or teleological processes.
From studies of the interaction of populations and their environments, bi- ologists have constructed their most basic paradigm. As Figure 3.1 indicates, the phenotypic properties of biological populations—that is, their morphology and behavior—are viewed as products of the interaction of their genetic heritage, or genotype, with their environment. These phenotypic properties of the population
2. In recent years, geneticists have increasingly distanced themselves from the view that all genetic material is useful or adaptive. Various explanations have been advanced to account for the existence of apparently maladaptive and nonadaptive genes, including “hitchhiking” and “selfish” genes. In the case of “hitchhiking,” natural selection affects clusters of linked genes, such as adjacent genes on the same chromosome. When selection favors a beneficial mutation in one gene, nonadaptive mutations in nearby genes can be “dragged along” if there is a net benefit (Charlesworth and Charlesworth, 2002). “Selfish” genes are, in effect, parasites that persist when there is an opportunity to produce extra copies of themselves relative to the rest of the genome. For example, some genes that reduce the fitness of individual organisms spread by a process called “meiotic distortion,” in which these genes manage to hijack the genetic process so that they are included in more than half the gametes (sperm or egg cells) produced by a parent that has only one copy of the “selfish” gene (Lyttle, 2002). In the case of redundant genes, current theory suggests that they may sometimes have utility in much the same way as back-up electrical systems in a hospital (Krakauer, 2002).
have no direct effect on the phenotypic properties of subsequent generations in this most general model. They have only an indirect effect that is mediated either through the gene pool or through the environment. Thus, by the process of natu- ral selection, organisms that bear certain genes develop morphological character- istics and behavioral patterns that enable them to be either more or less successful reproductively than others of their species. This causes their genes to become either more or less common in the population, and this, in turn, influences the phenotypic properties of the population in subsequent generations. Alternatively, the behavior of populations may alter the biophysical environment to greater or lesser degree (e.g., beavers dam streams, predators check the growth of prey popu- lations), and these changes may later have an impact on the morphology and behavior of the population itself.
This paradigm is of far greater importance to the study of human societies and their development than is generally acknowledged. For if the first premise of ecological-evolutionary theory is sound,3 human populations are subject to the
influences of genetics and environment just as all other populations are. Acknowl- edging this in no way commits ecological-evolutionary theory to reductionism, however, because the ways in which the paradigmatic model operates for different species varies greatly (see below). But these differences must be recognized for
3. See the first paragraph in the chapter.
Time 1 Time 2
Genotypic properties of a population: its gene pool and the information it contains The biophysical environment Phenotypic properties of a population: its morphological characteristics and behavioral patterns Genotypic properties of a population: its gene pool and the information it contains The biophysical environment Phenotypic properties of a population: its morphological characteristics and behavioral patterns
The Biological Foundations of Human Societies 37 what they are—namely, variations on a common theme, not totally different and unrelated processes.