Sartre? Genes talk?

"I am the only individual that any one of my selfish genes can be sure of." (Dawkins 106) That, right there is the fundamental point of existentialists such as Jean-Paul Sartre. The only reality that exists is you and nothing else. Going back to what I said in my previous blog, Dawkins is accidentally making some great points about humanity.
Another thing which has sparked my curiosity a couple of times throughout the novel is when Dawkins explains how a gene 'says' one thing or the other. For example: "A gene that 'says', in effect: 'Body, if you happen to be an adult male, defend the troop against leopards', could become more numerous in the gene pool." What does this mean? Genes give the body coded information through amino acids and consequently proteins. How in the hell could this eventually translate an if and then statement? How, for that matter, are any messages translated?