Why free will is an illusion that takes place of the reality of your dna's control over you

For example say you believe in free will. You might say to me that you are going to think about elephants, in order to prove that "you" have control over your thoughts and can choose to think about whatever you want to think about. However, in this instance as an example, your brain is actually under control of the bodies reward system, which structure is built by your dna. To go into detail what is actually happening is that the thought of elephants is not random, it just suits the situation as a thought that would be considered random, and when you think about elephants, your reward system is showering your brain in dopamine because following the thought process that leads to the thought of elephants rewards you because your brain then says "see im right, there is free will", and being vindicated and proven right in an argument is a decidedly rewarding experience. The fact is however that because you are thinking of elephants to get the reward of dopamine, you are under the control of your reward system and thus also under the control of your dna.
If i need to i will further explain why ther is no such thing as a random thought. It has to do with causality. Every thought has a string of neuron firings leading up to it basically.
Your dna builds your brain into a machine that looks out for your dna's interests such as preservation (manifested in fear of dying) and gene replication (why sex feels good)

Sparknotes. If you think that you have control over your thoughts, like you can force yourself to think about something, the reason you can do this and your brain doesnt wander around aimlessly is because you have a reward system which rewards your brain with dopamine for "staying on topic" and does not reward thoughts (neural pathways) that are not deemed pertinent or important by your reasoning center (something that is also built by both your dna AND your reward system)