As someone with a strong neurobiological foundation, I believe that the brain is the center of all behavior. What is the evidence for that belief? Remove someone’s brain and see if they have any behavior (note: I’m not endorsing this behavior, I’m merely postulating a hypothetical situation). Without the brain, there is no behavior. So, the brain is necessary for behavior but is it sufficient?
In psychology we often talk about necessary and sufficient conditions for behavior. That is, you may need a certain factor in order for a behavior to happen but without other factors, the behavior will not occur. For example, you need water to live – it is necessary – but you also need food, so thus not sufficient. So, the brain is necessary for behavior but can all behavior be explained solely by the brain? Another way of phrasing this question is, “Does biology determine all behavior?” The term for this belief is biological determinism.
To answer the question we first have to investigate and uncover other potential influences on (causes of) behavior. If behavior is biologically determined, do people have free will? That is, do people really have the ability to consciously make and choose different behavior? Or are all behaviors simply determined at the neuronal (or genetic) level and free will is only an illusion? This post is an expansion on one of my previous posts concerning alternative assumptions to naturalism in neuroscience.
If you really believe that the brain (and by reductionism, genes) are solely responsible for behavior, then you cannot believe that people have free will. You also cannot believe that the environment is directly responsible for behavior – it can influence it – but at the core, your genes and your neurons create behaviors. Alternatively, you can believe that humans have free will, that we can make choices because of or in spite of our biology. Agency can influence biology and biology can influence agency – they are not mutually exclusive categories. While the brain is a necessary condition for behavior, it is not sufficient; agency is a factor in human behavior.