The very idea seems both incongruous with reason, and profoundly perturbing…as truths often are.
There are two kinds of behavior: Innate and Acquired.
Innate behavior is that which we are born with. It is influenced by our genetic make-up, which in turn is the result of natural selection over many ages (or sporadic mutations within the same generation). In other words, this type of behavior is beyond an individual’s own control.
Acquired behavior is that which is shaped through environmental forces. Molding of such behavior begins from childhood and continues till death, depending on the type of environment(s) we go through. Since our environments are beyond our control, so are their effects on our behavior.
You may think that we are often capable of choosing the environments we expose ourselves to. That is incorrect, because such choices themselves are influenced by behavioral conditioning from environments we have previously been exposed to. For example, in a home where a child is taught to take good care of his personal hygiene will likely stay in places that are clean. The more he spends time in such places, the more accustomed he becomes to them. He may also spend more time with people who share the same interest in cleanliness as him. Thus commences a positive feedback loop in which he’ll become growingly concerned about good hygiene.
A perceptive reader may have noticed that this is not always the case. Quite often, we have children behaving completely opposite to how they’ve been taught to behave by their parents. How is that possible if free will is non-existent?
For two very good reasons. Firstly, our milieu is not nearly as simple as the one described in this example. It is a complicated mess of uncountable, indiscernible variables, each influencing one’s behavior in a different way. For instance, the same child who is taught that cleanliness is next to godliness by his parents, may be taught a different lessons by his peers at school, most of whom enjoy playing in mud. Ultimately, the shaping of his behavior will depend on which environment is dominant.
The other reason is his innate behavior. By the virtue of genetic variations and mutations, each one of us is endowed with a slightly different kind of behavior, arising due to differences in neuronal circuitries of our brains (the MAO-A gene has been implicated for hereditary tendency towards criminal behavior). Often, our acquired behavior conflicts with our innate behavior. When it does, the environmental factors have to be extra-strong to produce any behavioral alteration. Otherwise, they’d fail to exert any influence.
We are, at our most basic level, prisoners of the electric currents coursing through our brain.
A neuroscientist is able to work a human being like a puppet simply by using an electrode to stimulate or excite the right areas of his patient’s brain. He can make the patient move his hand by exciting a certain point of his motor cortex, or make his patient want to eat food by stimulating a group of neurons in his lateral hypothalamus. And the best part: the patient feels as if he’s performing such actions by his own volition!
We are the products of our genes and environments, and nothing more. What I’m typing is exactly what one would’ve expected me to type given my genetic make-up and the environment(s) I’ve been exposed to.
The free will theory defies both biology and physics. Biology, because we have no reason to expect such a thing to magically appear at this level of the evolutionary tree. Physics, because it deals in precise (or near precise, if you consider quantum mechanics) laws about how things work, and free will would mean complete stochasticity (randomness) that would play havoc with such laws.
The free will theory is accepted only because the variables involved in conditioning our behaviors are so numerous and complex, that it’s impossible to predict accurately how a person would behave. Otherwise, it’s nothing more than an illusion.