How Does Riht Happen?

When a child is made it, it is the combination of geans from both parents. Sometimes you get bad traits as well - if somebody has some genetic defect or some some inherited illness that also gets passed on. So certain recessiveo disadvantageous traits have passed on. But typically over long periods of time, what happens is that the people who in whom a disadvantageous traits are passed on, they don't survive. These are disadvantageus to your survival.