It has been a while since the last EvoMath. In this installment I am going to begin to discuss classical selection theory. Selection occurs when certain alleles are likely to transmit more copies of themselves to the next generation than other alleles at the same locus. The simplest way to think of this is in terms of the viabilitity of individuals. If an individual dies before it can reproduce, then it is not able to transmit its genes. If such a death was influenced by the genes it carried then selection can occur. Classical selection theory assumes that there exists viability selection and that it is constant, i.e. independent of allele or genotype frequencies. There is also theory behind frequency-dependent selection, but it beyond the scope of this article.