Chapters 3 & 4 (63-75; 83-84): Biology and Evolution
EVOLUTION AND CREATION STORIES
This chapter is about how biology and evolution have shaped our past and present. While all human behavior and characteristics can’t be explained biologically, there is no scientific debate about the fact that evolution exists, it connects all living things and explains many of the biological features we see in human beings. However, all human cultures have creation stories or myths that explain how humans came to be and our place in the world, in the animal kingdom and in relation to other peoples. These creation stories are different from evolution. Evolution relies on science to explain our species and is based on testable ideas. Religious beliefs about our origins are based on faith, a belief in things not seen.
The scientific method is a form of knowledge seeking that entails making observations, formulating a hypothesis, testing the hypothesis, and confirming, amending or rejecting the hypothesis.
THE CLASSIFICATION OF LIVING THINGS
This section explores the scientific approach to understanding humans. This approach involves evolution and the three processes of evolution: variation, heredity and natural selection. Evolution is “a process of cumulative change in the characteristics of organisms or populations, occurring in the course of successive generations related by descent.” Charles Darwin is responsible for formulating a theory of natural selection that helped to explain how species change over time, or evolve.
Natural selection is the process by which organisms that are better adapted to the environment reproduce more effectively and increase in numbers faster than less well-adapted forms. It is the driving force behind evolution and accounts for much diversity in the animal kingdom. Darwin included competition in his model of how natural selection drives evolution. Natural selection posits that, “because resources are finite, and because of random variation, some individuals will be better than others at accessing those resources. Those individuals will then gain enough of an advantage to produce more offspring than other individuals of the same species.” This advantage is really an increase in the animal’s fitness, or, “the probability that an animal will survive and reproduce.”
Variation - Darwin also noted the importance of the fact that no two individual animals are exactly alike in sexually reproducing animals; there are no clones. And it is these differences, no matter how small, that could make or break an animal’s chances of survival. Those that do survive, often because of those small differences, can then pass their genes, including those that code for that difference, down to their offspring. The ones who die will not get to pass their less well-adapted genes on, thus ridding the population of those bad traits. Presently, anthropologists explore many variations using the concept of clines, or gradual changes in the frequency of a trait (allele) over geographic space.
Heredity refers to inheriting genetic and physical traits from ancestors. Natural selection works only if offspring inherit features that confer greater fitness (adaptation). While Darwin understood that heredity existed, he came along before we understood fully the effects of genes or that DNA existed. We have Mendel to thank for working out the rules of genetic inheritance. His deductions led to the discipline of genetics (the field of biology that studies heredity). While Mendel figured out heredity, he didn’t understand genes (the smallest unit of heredity), which had yet to be discovered.
HOW EVOLUTION WORKS
This section examines how evolution works on three levels. The first is microevolution (the processes that work at the level of an individual over shorter periods). The second is midway between micro and macro evolution and explores how evolution operates on populations. The third is macroevolution (processes that operate on a large scale and over long periods of time).
At individual levels, the study of genetics illustrates how parents pass traits on to their offspring.
Evolution within Populations
This discussion of evolution has so far dealt with individuals. Midway between microevolution in individuals and macroevolution of an entire species are forces that work on populations (a group of individuals that can and do interbreed). A population has a gene pool (the total possible genes of a population). What matters in populations in regards to evolution are the frequency and distribution of individuals who carry certain types of genes. A number of things can influence variation within a population.
Macroevolution operates at the level of the species and includes large-scale changes.