Question

How are undesirable traits filtered out through natural selection

Answer 1

Natural selection is the differences in survival and reproduction as the consequence of differences in genotypes and, consequently, phenotypes.  It is one of the factors of evolution that affects a frequency of different variations. In natural selection, genotype variations that will increase the chance of survival and reproduction of some organism are preserved and will be inherited Thus, "good genes" will be inherited. The undesirable traits will be inherited in very little rate, so, that way they are filtered out through natural selection.