Obligate vs. Facultative Adaptations

David Buss, a leader in evolutionary psychology research, lists six properties of evolved psychological mechanisms in his textbook, Evolutionary Psychology: The New Science of the Mind:

1. An evolved psychological mechanism exists in the form that it does because it solved a specific problem of survival or reproduction recurrently over evolutionary history

2. An evolved psychological mechanism is designed to take in only a narrow slice of information.

3. The input of an evolved psychological mechanism tells an organism the particular adaptive problem it is facing.

4. The input of an evolved psychological mechanism is transformed through decision rules into output.

5. The output of an evolved psychological mechanism can be physiological activity, information to other psychological mechanisms, or manifest behavior.

6. The output of evolved psychological mechanism is directed toward the solution to a specific adaptive problem.

Within these mechanisms are two different types of adaptations: obligate and facultative. Obligate adaptations are the same no matter the specific environment, but facultative adaptations are sensitive depending on the environmental variation. For example, the fact that sugar tastes sweet and the pain of scraping your knee would not change if they were experienced in a different environment. However, if when very young a person was often lied to or had promises broken by a parent, they may eventually have trust issues because of it. Their sense of trust as an adult depends on whether their parents or guardians were reliable. Evolutionary psychologists hold that facultative adaptations work like "if-then" statements.

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