Sociobiologists believe that human behavior, as well as nonhuman animal behavior, can be partly explained as the outcome of natural selection. They contend that in order fully to understand behavior, it must be analyzed in terms of evolutionary considerations.
Natural selection is fundamental to evolutionary theory. Variants of hereditary traits which increase an organism's ability to survive and reproduce will be more greatly represented in subsequent generations, i.e., they will be "selected for". Thus, inherited behavioral mechanisms that allowed an organism a greater chance of surviving and/or reproducing in the past are more likely to survive in present organisms. That inherited adaptive behaviors are present in nonhuman animal species has been multiply demonstrated by biologists, and it has become a foundation of evolutionary biology. However, there is continued resistance by some researchers over the application of evolutionary models to humans, particularly from within the social sciences, where culture has long been assumed to be the predominant driver of behavior.
Sociobiology is based upon two fundamental premises:
- Certain behavioral traits are inherited,
- Inherited behavioral traits have been honed by natural selection. Therefore, these traits were probably "adaptive" in the species` evolutionarily evolved environment.
Sociobiology uses Nikolaas Tinbergen's four categories of questions and explanations of animal behavior. Two categories are at the species level; two, at the individual level. The species-level categories (often called “ultimate explanations”) are
- the function (i.e., adaptation) that a behavior serves and
- the evolutionary process (i.e., phylogeny) that resulted in this functionality.
The individual-level categories (often called “proximate explanations”) are
- the development of the individual (i.e., ontogeny) and
- the proximate mechanism (e.g., brain anatomy and hormones).
Sociobiologists are interested in how behavior can be explained logically as a result of selective pressures in the history of a species. Thus, they are often interested in instinctive, or intuitive behavior, and in explaining the similarities, rather than the differences, between cultures. For example, mothers within many species of mammals – including humans – are very protective of their offspring. Sociobiologists reason that this protective behavior likely evolved over time because it helped those individuals which had the characteristic to survive and reproduce. Over time, individuals who exhibited such protective behaviours would have had more surviving offspring than did those who did not display such behaviours, such that this parental protection would increase in frequency in the population. In this way, the social behavior is believed to have evolved in a fashion similar to other types of nonbehavioral adaptations, such as (for example) fur or the sense of smell.
Individual genetic advantage often fails to explain certain social behaviors as a result of gene-centred selection, and evolution may also act upon groups. The mechanisms responsible for group selection employ paradigms and population statistics borrowed from game theory. E.O. Wilson argued that altruistic individuals must reproduce their own altruistic genetic traits for altruism to survive. When altruists lavish their resources on non-altruists at the expense of their own kind, the altruists tend to die out and the others tend to grow. In other words, altruism is more likely to survive if altruists practice the ethic that "charity begins at home."
Within sociobiology, a social behavior is first explained as a sociobiological hypothesis by finding an evolutionarily stable strategy that matches the observed behavior. Stability of a strategy can be difficult to prove, but usually, a well-formed strategy will predict gene frequencies. The hypothesis can be supported by establishing a correlation between the gene frequencies predicted by the strategy, and those expressed in a population. Measurement of genes and gene-frequencies can be problematic, however, because a simple statistical correlation can be open to charges of circularity (Circularity can occur if the measurement of gene frequency indirectly uses the same measurements that describe the strategy).
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