The problem is that many deleterious mutations are NOT selected out; they produce genetic disease that a person may simply have to live with. If the disease is horrible enough then the person will suffer for years and eventually die of it. Is that what is meant by "selection?"
That's because you are including human medicine in your logic. Sure if a human baby is borne without the ability to produce insulin he can have a normal life with treatment. but if a deer somewhere in the wild is borne with the same mutation it will die before it gets to procreate. hence weeding out that bad mutation from the population. And even if by some miracle it gets to procreate its children are still going to have a much higher chance of not procreating weeding the mutation out eventually.
Christianity, One woman's lie about an affair that got seriously out of hand
What are the Christians gonna do to me ..... Forgive me, good luck with that.