The Epigenetic Hypothesis and the New Biological Role of Self-Identified Racial Categories

In biomedicine self-identified racial classifications of humans are used to infer genetic differences causally responsible for different susceptibilities to complex diseases between racial categories. In this paper I analyze the epistemological status of these classifications within the three main types of hypotheses that explain the epidemiological differences between racial categories: the genetic, the epigenetic, and the environmental hypothesis. These hypotheses differ in the use of self-identified racial classifications as proxies respectively for genetic, epigenetic, and environmental differences causally responsible for differences in the risk of complex diseases between racial categories. I show that the use of self-identified racial classifications under the genetic hypothesis is not justifiable from an epistemological point of view, and recent biological evidence rather highlights the relevance of different kinds of nongenetic factors in the causation of specific susceptibilities to complex diseases, therefore supporting both the environmental and the epigenetic hypotheses. My conclusion is that the use of self-identified racial classifications may be justifiable only under either the environmental or the epigenetic hypothesis. In particular, the biological role of self-identified racial categories as models of an epigenetic kind of variation within the whole human population may be relevant in the investigation of epigenetic mechanisms causally responsible for susceptibilities to complex diseases.