I. Evolution is directional change and is the primary way that we understand the biological history of humankind.
1. The processes of evolution shaped humans’ brains and bodies.
2. It has also shaped our capacity for culture.
II. Charles Darwin’s theory of natural selection proved the most convincing scientific explanation of the variety and history of life on earth.
1. Natural selection—the mechanism of evolutionary change; changes in traits of living organisms that occur over time as a result of differences in reproductive success among individuals.
2. Darwin’s evidence and assumptions:
1. Observed that no two living things, even those of the same species, are quite alike. Sources of variation:
1. Mutation—a random change in genetic material; the ultimate source of biological variation.
2. Gene flow—sexual reproduction and the movement of individuals and groups from place to place result in the mixing of genetic material.
3. Genetic drift—changes in the frequencies of specific traits caused by random factors.
2. Observed that most creatures, human and nonhuman, did not survive long enough to have offspring.
1. Organisms fell victim to predators, contracted diseases, or perished through some defect in their biological makeup.
2. Before the development of sanitation in the 19th century and antibiotics in the 20th, the vast number of human children also died young.
3. In the world’s poor nations, large numbers of children die before they reach the age of five.
3. Darwin was profoundly affected by the philosophical works of Adam Smith and Thomas Malthus who both emphasized the role of competition in human social life.
1. In the 1770s, Smith argued that competition among firms increased their productivity and led to social betterment.
2. A quarter of a century later, Malthus wrote that, because human population levels rose much faster than agricultural production, struggles over resources were inevitable.
3. Darwin, synthesizing these two positions, argued that creatures with traits that suited them well to their environment tended to win the struggle for nutrition and reproduction.
4. Darwin further argued that those who won this struggle for survival were able, in some way, to pass some of the traits that led to their success to their offspring.
1. Darwin reasoned that, over the course of millions of years, this process could give rise to new species and all of the tremendous variation of the natural world.
2. Darwin’s theory is sometimes referred to as “survival of the fittest,” but this phrase was coined by the social theorist Herbert Spencer, not by Darwin himself.
3. Strength and intelligence do not necessarily guarantee reproductive success, and are not important for all creatures and environments (such as the South American tree sloth).
III. Virtually all of the debate about evolution is religious and political rather than scientific.
1. Evolution challenges a literal reading of religious stories. However:
1. Many theologians agree that evolution is consistent with the teachings of their traditions.
2. In 1950, the Catholic Church declared that evolution was compatible with Christian teachings.
2. Today, there is no meaningful scientific challenge to evolution. Still:
1. Scholars argue about the speed of evolution and the precise conditions under which it occurs.
2. There is much discussion about the historic relationships of plants and animals and how they should be classified.
3. Scientists may debate the appropriate evolutionary place of specific fossil human ancestors.
IV. Modern-day humans, gorillas, and chimpanzees evolved from a common primate ancestor.
1. All animals are all equally evolved.
2. Biological anthropologists use the fossil record, DNA studies, and immunology to try and determine the common ancestry of humans and other primate species.
1. Creatures that became humans and apes split from those that gave rise to the monkeys of Europe, Asia,