In my opinion I feel that because when two human beings create another they share their genes with the new human being. As that human grows up it does the same thing. It's known as a cycle. I'm guess that there will be a time where two healthy people will decide to reproduce and will create a healthy baby. Although I'm not all sure.
Sexual reproduction involves the genetic material of two organisms instesd of one. Since the resulting offspring will contain genetic material from two organisms instesd of one, there is more genetic diversity in the offspring.
