Hard determinism cannot explain the existence of play. Let me define play as the exercise of one's capabilities in an activity that has no practical goal. Exercising one's capabilities in play is apparently motivated by the sheer pleasure of doing so. In any case, what I want to establish is that play is not a product of determinism, but of free will.
Evolutionary theorists believe that play has long-run survival value, even if it has no immediate goal. That is why I defined it the way I did: As exercising one's capabilities. It has been shown to improve the efficiency of neural networks.
"Marc Bekoff (a University of Colorado evolutionary biologist) proposes a 'flexibility' hypothesis that attempts to incorporate these newer neurological findings. It argues that play helps animals learn to switch and improvise all behaviors more effectively, to be prepared for the unexpected." http://en.wikipedia.org/wiki/Animal_play#Play_and_animals
I find Bekoff's hypothesis to be an excellent definition of free will. But could play instead be determined by some prior cause? I think not. Evolutionary theorists know that explaining the survival value of a trait, or why it has been "selected for," does not at all explain its cause, or why it was there to be favored by natural selection in the first place.
It is my impression that play is found primarily in mammals, which are more intelligent than other classes of animals. Thus it seems that play--and free will--is enabled by higher intelligence. In a more immediate sense play is enabled by having one's pressing needs satisfied, by being in a safe situation, and sometimes by having a willing play partner or partners. But these preconditions do not in any sense determine the act of play. Play does not happen in any automatic, mechanical, or unconscious way as a result of these preconditions.
Perhaps play is motivated by the pleasure it is expected to bring, and perhaps that pleasure is triggered by dopamine in the neural circuits when they are exercised. But here we are talking the language of free will: Choosing to engage in an activity that is unnecessary, non-essential, not determined by any prior cause, and making that choice because of the pleasure anticipated from it, even though that pleasure does not signal the satisfaction of any real need.
So far I have been discussing the kind of free will that mammals in general apparently have. It is, let me note, not the kind of free will that the soul was supposed to have. Pious souls did not play or seek pleasure, especially not on Sunday, when piety was commanded by God. Besides, rats, cats, and hamsters were not supposed to have souls.
The kind of free will that souls were supposed to have was more like "free won't:" moral self-control. This form of free will may be unique to humans, but not because we have souls. I will not attempt a scientific explanation of moral self-control here, but only emphasize that it is found not just in church, but in the impious, pleasure-seeking realm of human play. Most forms of human play, be they sports or dance, music and art, have rules. Only humans are capable of conforming to the rules, and they will be penalized in the game if they do not. Humans enforce the rules on each other with penalties, not as revenge, but as deterrence: The players will generally choose not to violate the rules to avoid the punishment. (The ones who do violate the rules often do not expect to get caught. Need I mention Lance Armstrong?) Please notice that this is all described in the language of free will, not the language of determinism.
Okay, I found out why I'm not getting notifications of new comments and have corrected the situation. I'll be responding more promptly in the future.
Now . . . let me read this post and mull it over . . .
Hard determinists will (wrongly) claim that if something serves a purpose, there is a reason (cause) and is thus deterministic. Play, for instance, could be (and probably is) instinctive in immature mammals and is thus a genetically preprogrammed activity; causally deterministic. The problem with this is that, while play may be an instinctive impulse in the young, that doesn't mean it can't also be engaged in voluntarily -- much the same way that sex is an instinctive impulse but can also be engaged in voluntarily. Such tendencies, to simplify by claiming one cause or kind is the only possible cause or kind, seems to surface a lot with hard determinists. They apparently like neat packages. And false dichotomies.
One reason hard determinists manufacture false dichotomies is because they fail to recognize causal distinctions between inanimate objects and (intelligent) animate beings. Inanimate objects can be analyzed and understood through their physical properties. They are amenable to material reductionism. They can be broken down to their elements and compounds which, in turn, can be reliably recombined to produce specific results or products. Although animate beings are also physical entities, they are of a different category: they're biological beings. They are not amenable to material reductionsim because, unlike inanimate objects, they DO things. Not only do they do things . . . their constituent parts also do things: like replicate, respirate, digest, communicate, defend themselves, etc. Inanimate objects exist. Animate beings live. It's the difference between linear causality and reciprocal causality.
By applying the physics of the inanimate realm to the biology of the animate realm, hard determinists are completely missing the mark. The differences are so obvious that I can only surmise they ignore them out of sheer dogmatic stubbornness.
Once you acknowledge the differences, you can then see the potentials offered by biology: potentials from evolution, emergent phenomena, feedback systems, etc. that involve interaction (not mere physical reaction) with causality: reciprocal causation instead of mere linear causation.
Animate beings are agents. They DO things. They evolve specialties: abilities and competencies that enable them to survive and reproduce. And it's all about causality -- abilities and competencies evolve to interact with causality. The reason for this is that causality is consistent and persistent. It provides something we can count on not changing, ever.
Causality, cause and effect: it's binary. It doesn't get much simpler. Causality is the 'machine language' of physical laws. If you want to interact with the world, you have to speak the language. Mother nature is fluent in causality. The biological dialect of causality is evolution. All of life is evolved to interact with causality. Humans are the evolutionary pinnacle of life on Earth in terms of our expertise with causality.
Free will? Not a big deal for us. We routinely manipulate events and stamp our own intents on the future. It's part of our human intelligence . . . part of what makes us human.