Scientifically it is very simply. We shoot deer. Therefore the deer we don't shoot must have some advantage whether better since of smell, sight etc. We are selecting these deer that have not been shoot to breed with other deer and pass along those genes to their offspring. Then those deer have it and so forth. By us shooting young or old bucks (mostly we get the suggested dumber deer or deer that lack some special trait to help them survive the hunting season) this leaves the smarter deer (ones that have an advantage) to breed and pass along those traits. It is like darwin said, the strongest will survive. In a round about way these deer are harder to kill because of us...