Note that the question of free will simply does not arise for animals.  We think that, even for intelligent species, their behavior follows from complex interactions among their individual genomes and epigenomes, their internal and external environments as both shaped and shaping, and their experiential histories from birth on.  We don’t think we could predict with total accuracy what an individual animal will do in a given situation, but that is only because we realize the interactions that lead to animal behavior are complex and happen at many different levels from the most micro to the most macro.

Humans often say that they are far more intelligent than any animal.  They will say things like “A dog has the intelligence of a two-year-old”.  But, of course, they stack the deck in their own favor by choosing a definition of “intelligence” that favors only them.  If we choose a fairer definition—one like “intelligence is the ability to face and solve the problems one faces in life”—then most animals impress me as more competent that most humans.  Humans in so many ways—as individuals and as groups—undermine themselves and bring on more problems than they solve.  No animal has our ability to undermine ourselves and screw things up for all life on earth, ourselves included.

So, what do humans have that other animals do not, if it isn’t intelligence?  What we have is a mental capacity to “theorize”.  By this I mean a capacity to make up stories about why things happened and about what might happen.  We are aware of death and of the possibility of ever greater pain.  We alone can be worried that things happen randomly, probabilistic, and sometimes for no “good reason”.  We alone can worry about our place in the universe and what it all means.  Other animals don’t.

Our capacity to theorize gives rise to very mixed blessings.  We are driven by stress, anxiety, and fear more than any other creature.  We can do science and make medicines that save us from pain, though often we then misuse them to ultimately bring on more pain and suffering in aggregate.  We can make up religions to comfort us in the face of death and then use them as a license to bring death to others.  We humans will most often choose a theory/story that is comforting, but false, over a theory/story that is true, but not comforting.

So, human action is a product of complex interactions—most of which individual humans have no conscious awareness of and which even science is confounded by—and often largely deceptive theories (confabulated stories).  To see such actions as the product of “free will” is a comforting story, but, in all likelihood, false.  A choice is hardly “free” if we make it on the basis of very little of the processes and evidence relevant to it.

A small part of our brain is conscious and most of what goes on in the brain and body leading to feelings, beliefs, and actions is not open to conscious awareness.  Yet the small—and poorly informed—conscious part of our brain confidently confabulates and firmly believes that we have made free and informed choices.

This idea—that free will does not exist—is not one most humans or society can live by.  While we don’t live in a ­­mechanical clockwork determinist universe, we do live in a world of inconceivable complexity that often rules out successful prediction, even about ourselves.  The leading emotion this realization leads to is massive wonder to the point of bewilderment, an emotion that we often try to tame or “normalize” with stories, religious and otherwise, that tell us that things “happened for a (good) reason”.

It does appear that humans do not have free will in the sense of the term as we humans usually understand it.  Yet, we are not “determined” in any simple sense at all.  Our actions, beliefs, and feelings are the outcomes of an immense number of process in us, outside us, and in interactions between the two, at all different (but interacting) levels.  Little of these processes are open to conscious awareness and much is still poorly understood by science at this point.  These outcomes are the product of a complex system, or better of different complex systems interacting with each other.  Such complexities mean that with even small changes—even random changes—in the interacting processes, the outcomes could well have been different, even very different.

At this level of complexity, the notion of “free choice” is a prosocial notion necessary for the existence of society (and law), not an empirical reality at the level of “nature”.  Without people accepting that they make free choices and are responsible for the outcomes of those choices (within limits), society could not exist, nor could collective action.

As an aside, I should mention that religion often has a contradictory relationship to free will.  Some religions say humans are free to choose, but that if they make the wrong choices—choices they know they should not make if they have kept up with their religion—they will be punished in the “next life”.  It is hard to see a choice as free when I have already told you that if you choose “door X”, you’re going to hell.  Worse yet, some religious people see this “forced choice” situation as a “gift” from God, rather than a cruel game, especially since, God being all-knowing, “He” already knows what choice you are going to make, but, nonetheless, let’s you hang yourself anyway.

Animals, of course, do not sit around worrying about the meaning of it all in a world where our choices are illusory.  They get about the business of living—and it appears that while some religious people believe they can go to heaven, no one seems to think they can go to hell (because they don’t have “free will”).