PART IV. PHYSICAL AND SOCIAL EVOLUTION OF HUMAN BEINGS
The first three themes of this book (life is chemistry, chemical life developed through evolution, and evolution takes places in an ecological context) are followed in this part dealing with the evolution and nature of human beings. Chapter 13 discusses the process of evolution through natural selection. Chapter 14 stresses the importance of the social evolution of animals. Chapters 15 and 16 discuss the evolution of humans in both a physical and social context.
Many observers try to find moral lessons in nature. This moralistic approach should have no place in science. The behavior of animals primarily depends on environmental responses within an ecological context and not to any pattern that is morally better and therefore more adaptive. The sociobiology of animals will help combat America's moralism.
CHAPTER 13. EVOLUTION
Evolution is the process which explains how life developed from a replicating aggregation of chemicals to human beings. This chapter explains the concept of evolution, a concept that most people do not really understand. Humans are linked to other species both through evolution and ecology. Without an understanding of the other species, humans cannot fully understand themselves. The chapter also emphasizes that evolution takes place within an ecological context. It is impossible to fully understand evolution without understanding the ecological interrelationships between the different species of life and the physical settings in which they live and die.
Genetics and Evolution
The genesis stories of the world's religions provide answers not only to the age old question of how life arose, but also to the question of why there are so many different species. This religious explanation proved acceptable until the nineteenth century A.D. when the theory of evolution began to be formulated. Charles Darwin published his On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life in 1859. His ideas met considerable criticism from many corners. In America, scientists rejected Darwinism for the adaptation model of Lamarck. It was not until the rediscovery of Mendel's system of genetics in the early twentieth century that the idea of evolution triumphed in the natural sciences. Evolution, however, never triumphed in the social sciences, as will be shown in a later chapter.
Within all species, there is a great deal of variability in physiology. This variability is the result of constant genetic changes produced via such forces as gene recombination and natural mutations. Mutations are especially important, because they are a major cause of the evolution of new traits.
The basic theory of evolution maintains that because there are limited resources available to species, these species compete in a struggle for existence. Those species that have characteristics better adapted for survival are able to succeed in this struggle. Those that are not well adapted perish. Through this process, there is a natural selection of those species with traits adapted for survival. Of course, not all survival is based on the adoption of more adaptive bodily features. For instance, biologists have arbitrarily lengthened the tail feathers of certain male birds and found that the female birds prefer the artificially altered males to the normal males. Obviously, the elongated tail characteristic may even be a maladaptive feature in that flight can become more difficult. This means that natural forces would be more likely to select those males with longer tails, and hence the entire species, for extinction.
Modifications of the Theory of Evolution
Since 1859, there have been several revisions of the theory of evolution. Biologist Stephen Jay Gould (1980) modified the theory to account for the seeming paucity of fossils at critical pints in evolutionary history. Gould found that evolutionary change can actually occur very quickly. Biologists now think that species go long periods of time, hundreds of millions of years, without any change, and then suddenly certain species undergo a comparatively short, but frantic, burst of evolutionary activity.
These explosions of evolutionary development arise when the natural ecology of an area is disturbed and new ecological niches are created. Niches are sources of food (and thus of energy) that can support a species. The great abundance of niches insures that the naturally occurring mutations that always happen will be able to find homes for themselves. This process continues until virtually all of the environmental niches are filled. An example is the great proliferation of larger mammals after the disappearance of the dinosaurs.
Another modification of evolutionary theory came with the sociobiological study of the evolution of altruism among species. The sociobiologists found that organisms behave altruistically in order to continue the genetic line of their family and social group. Furthermore, these genes operate to insure continuation, not just in the next generation, but in future generations as well. We will defer a more complete discussion of this genetic function until the chapter on social evolution.
The Effect of Ecology on Evolution
The importance of ecology can be illustrated by its impact on evolution, for evolution actually takes place within an ecological context. Indeed, one cannot understand systematics and evolution without ecology. For instance, by the start of the Cambrian period, most of the evolutionary development of animal phyla had occurred within the sea. To fully understand the nature of these early animals, we have to study the ecological interactions within this underworld environment. One would have to study the interactions in the Cambrian seabed between sponges, coelenterates similar to sea-anemones, and various segmented worms, as well as echinoderms, mollusks, and chordate predecessors. We would also have to study animal interactions with species from kingdoms Prokaryotae, Protoctista, and Fungi. These interactions naturally select different species for survival. Unfortunately, this study of ancient seas is beyond this text. But it is the kind of subject that has to be studied if one is to fully understand the development of life.
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