 'The assumption that only the genes are evolved reflects a widespread misconception about the way natural selection acts.Genes are the so-called units of selection, which are inherited, selected, or eliminated, and so they are indeed something that evolves.But every time one gene is selected over another, one design for a developmental program is selected over another as well; by virtue of its structure, this developmental program interacts with some aspects of the environment rather than others, rendering certain environmental features causally relevant to development.