Selecting animal models of human aging: Inbred strains often exhibit less biological uniformity than F₁ hybrids

Most gerontological research is conducted using inbred strains of animals in an attempt to maximize phenotypic uniformity within experiments and thus increase the experimenter's statistical power to detect treatment effects. However, for a wide range of phenotypic traits, F₁ hybrids between inbred strains are considerably less variable than the parental inbred strains themselves. Therefore, the use of F₁ hybrids is preferable for many research applications. In this article, we discuss the sources of phenotypic variability and explain why F₁ hybrids are often less variable than inbred strains; we review the empirical literature illustrating the large range of species and traits for which this is true; and finally we suggest how this finding suggests that F₁ hybrids may often be superior animal models for studying the aging process and how to manipulate it.