There is something that you may have failed to consider - learning.
Do tell what you have learned that affects your control over your bodily functions?
Do you know of any one who can play the game chess with out learning the rules first?
Are you comparing a living body to a chess game? You're gonna lose the game eventually, regardless what you consciously choose to do to make your body function at peak performance. Healthy diet, exercise, vitamin supplement? It is just a tad more complicated than that.
p.s. the rules of the game of life is encoded in your DNA. That's the "learned" program and it is an exquisitely tuned game being played inside you without your consciously learned knowledge.
p.p.s. "evolution" and "natural selection" are the natural "learning" processes of all things.
I believe it's called "epigenetics".
But perhaps you are a little naive in viewing your body and its activities. Chess is a childs game compared to the game of life that goes on inside you without you even being aware of it. It's only when things go wrong that your conscious brain gets "notified" with a demand for corrective action. That's when we go to see a doctor.
Once learned every move is calculated, deliberate and self determining. Every move made is done freely and is dependent on how well you apply the rules for your own self benefit.
Ask your heart and your lungs and the flora in your guts, how they decide to keep functioning day after day for some eighty years, without your conscious participation.
Certainly that dang butterfly a few billion years ago didn't teach me how to play chess as I had to teach my self by my own self determination.
Really? Butterflies were using the airstream for millions of years when you were still a probability to fly thousand of miles to their breeding grounds.
Who made those travel arrangements? Bacteria and pure chemistry!!
Your body is engaged in an incomprehensibly large chess game among billions of bacteria and chemical chess moves.
If that and millions of other similar examples is not sufficient to show self determination at work I really don't know how it can ever be.
That's the illusion.
You don't need a brain at all to be alive and functioning. The paramecium does quite well even without a neural network, let alone a brain.
If a brain is necessary, how do these organisms manage to live?
Watch this Drew Berry clip of what goes on inside you every second of the day and night, without you being the least aware of it.
and this newer one;
These animations show cellular biology on the molecular scale. The structure of chromatin, the processes of transcription, translation, DNA replication, and cell division are shown. All animations are scientifically accurate and derived from molecular biology and crystallography research.
Note the magnification levels of the representation of various epigenetic activities.
Our bodies are biological universes! The numbers of active parts inside your body are astronomical.
Now there's a chess game, being played with exquisite precision, completely independent from our conscious decision making processes.
