I have concluded that while both genes and the environment (cultural and physical) are major determinants of human behavior, every human still has, at least in certain circumstances, what is traditionally called free will. I reject the totally deterministic, and especially the atomic-deterministic interpretation of reality. My rejection of the deterministic hypothesis is not because I find it repugnant, but because I find it to be (partially) misleading and counterproductive.
I am not rejecting causality. My understanding of causality is complicated, not simplistic. To the extent that human decisions are subject to free will, they would also become part of the chain of causality.
Our typical modern picture of the deterministic universe comes from classical, Newtonian physics. In the simplified version of this causality is like a well-constructed set of falling dominoes: once set in motion, it never veers off course. Atoms crashing into atoms form the air, and their micro-movements form the local weather: everything happens because of strict rules of mass, momentum, electricity and other forces.
I do not base my rejection of strict determinism on quantum physics. Causality in quantum physics (the kind studied by scientists, not the new age pseudoscience, pop culture version) is more complicated than classical causality. In some situations the causality is probabilistic. This is related to my free will argument not because it shows Newton was wrong, but because it shows you have to be careful about thinking about our complicated universe. Generally speaking, quantum causality only is an issue in the sub-nano end of the size spectrum.
The common, mistaken view of decision making posits that atoms, molecules and larger structures of the brain are deterministic from the atomic level up. It follows that "making a decision" is simply a name humans give to the compulsions that come from their atomic programming. Unlike mystics and spiritualists, I do believe this atomic viewpoint has some explanatory value. The brain is made up of atoms, molecules, neurons and other cells, and importantly the synapses between the neurons. Sometimes human activity can be attributed to causes from below, as when a clogged blood vessel leads to neural malfunction or death and the kind of strange behaviors sometime seen in people suffering from a stroke.
But causality also comes from outside the brain. It mostly comes from outside the brain. Without sensory experience the brain would learn nothing and do little. Without cultural input the behavior of humans would be the behavior of animals.
Cultural input from other human beings is (almost always) the main driver of behavior of any particular human being. Put two genetically identical babies in two different cultures (whether two families, or two nations) and they will grow up to reflect their cultural background. There are vast chains of transmission in human cultures, both horizontally in the present time and going back in time to the dawn of language and differentiation from the apes.
Humans make such a wide variety of decisions that lumping them all together can be uninformative. I want to focus on decisions that illustrate free will, even though those are also a large, diverse group of different kinds of decisions.
The (pre-Newtonian) classic exercise of free will was characterized as the decision to commit or not commit a specific sin. I am not concerned with divine punishment, but a religious person making such a choice could be. Religion is a learned culture. Drop a baby among the Islamic faithful, and (in traditional cultures were no other choice was available) the adult would be Islamic. Drop the identical baby into a Hindu culture and an adult Hindu would emerge. In diverse cultures like the United States, where children are almost always, at some point, exposed to other religions, free will might be exercised by the choice of another religion, or of no religion.
Suppose a person needs to make a decision, and that there are two clear choices. One involves a clear personal advantage, say not being hungry. The other involves a sin (or ethical breech), say taking food that belongs to someone else, the loss of which could cause them to go hungry.
We know that in this situation some people will steal and eat the food, and others will go hungry, perhaps even to the point of starving to death. The cultural restraint will have been imprinted in the brain from outside, over a period of years. If it is followed, it makes sense to say that behind the atoms in the neural synapses correspond to causation that can fairly be described as a system of culture. On the other side, of the person who steals and eats, we could say that hunger, which is some sort of impulse to eat arising in the neurons, overcame the fear of breaking the taboo against stealing. But excepting for the impulsive case, where little thinking is involved, in most cases there will be a weighing (by the person, the brain, or if you prefer, the synapses) of factors that determines the outcome. This weighing relates cultural inputs to the feeling of hunger, and may involve some amount of thinking, conscious or unconscious. Fear of punishment by gods or by legal authorities may be met with rationalization (say, "but a good God would want me to eat, and has provided this opportunity to eat. It is just food, it is not like robbing a bank or stealing an automobile.")
To say this complicated process is determined by atoms and electrical forces instead of culture, including language, rules of ethics, and metaphysical beliefs, is itself a culturally determined opinion.
A strict determinist (of the simplistic type) would argue that whatever cultural experience the individual had, the resulting structure of the brain atoms would still determine the outcome. But suppose someone else steps into the scene: the owner of the food, or a policeman, or a former schoolteacher, or a hungry, dying son or daughter, or a stranger who may or may not care about what happens. Behavior may change in that case. Perhaps the potential thief no longer feels that free will can be exercised. But in any case it is clearer that atoms, as atoms, are not the sole causal factor in the decision. Something very complex has become part of the chain of causation. Only the most obstinate, idiotic strict atomic determinist can claim that complex objects or humans cannot affect a human decision in such a situation.
Free will derives from the fact that the decision making process takes place. Decisions are not always about ethics. An artisan might have trouble deciding between two tools or approaches that could be used to achieve a goal. A writer might choose between two ways of expressing an idea or describing an event. Choices, thinking, and decisions are everyday human activities.
It is arguable that free will, or decisions made using free will, can cause material objects, or at least human muscles, lips and limbs, to move. A riot may start, and a kingdom may crumble, when one member of a crowd decides to throw a stone, turning the crowd into a mob, and unrest into a revolution.
Determinism is (or should be) a complex idea, and free will can be part of it. Our free will determines the future, usually in small ways, but sometimes in large ways.
The early Newtonian view was not about atoms. In Newton's universe planets, which can be idealized as masses, hurled around the greater mass we call the sun. The parts of the planet, including the atoms and atomic particles and subatomic particles, were just along for the ride.
The key here is to not let one metaphor blind you to the complications of reality. In some cases it makes more sense to say the planets and the force of gravity determine the future. In other cases it is fair to say DNA or cell structures, atoms or quarks determine the future. But for most cultural interactions, culture determines the future, and free will is there to make the call when choices need to be made.
Nature and nurture are both important, but what makes us truly human is free will.