Psychology and biology

A long standing question in philosophy and science is whether there exists an invariant human nature. For those who believe there is a human nature, further questions include:

• What determines/constrains human nature?
• To what extent is human nature malleable?
• How does it vary between people and populations?

Since human behavior is so diverse, it can be difficult to find absolutely invariant human behaviors that are of interest to philosophers. A lesser (but still scientifically valid) standard for evidence pertaining to "human nature" is used by scientists who study behavior. Biologists look for evidence of genetic predisposition to behavioral patterns. Human behavior can be influenced by the environment, so penetrance of genetically predisposed behavioral traits is not expected to reach 100%. A type of human behavior for which there is a strong genetic predisposition can be considered to be part of human nature. In other words, human nature is not seen as something that forces individuals to behave in a certain way, but as something that makes individuals more inclined to act in a certain way than in another.

Evolutionary psychology (EP) posits that the mind is made up of a massive number of interacting emotional, motivational and cognitive adaptations or "mental modules." EP seeks to identify which human psychological traits are evolved adaptations - that is, the functional products of natural selection or sexual selection. Adaptationist thinking about physiological mechanisms, such as the heart, lungs, and immune system, is common in evolutionary biology. Evolutionary psychology applies the same thinking to psychology, arguing that the mind has a modular structure similar to that of the body, with different modular adaptations serving different functions. Evolutionary psychologists argue that much of human behavior is the output of psychological adaptations that evolved to solve recurrent problems in human ancestral environments. This view has been critiqued as essentialist by some, and as neglecting "natural" genetic, environmental and individual variation (and that the closest you can come is norms of reaction), and as equivocating between the levels of genes, developmental programs, and actual human psychology/culture, and between individuals and population averages.