In this paper, we will discuss the notion of inertia in Classical Mechanics and its possible counterparts in Theoretical Population Genetics. We will show that, in Population Genetics, changes take place in a mathematical space whose structure is not compatible with notions such as the conservation of momentum or of angular momentum. In spite of this difference, we will argue that there is a fundamental analogy holds between the two fields. The principle of inertia describes the behavior of a system when nothing acts upon it. In Mechanics, this behavior is described by the conservation of momentum. We will show that different situations may be analogous to inertia in evolution. In particular, Theoretical Population Genetics uses a similar line of reasoning in at least two cases: random genetic drift, and geometric growth. However, we will argue that genetic drift is mathematically very different from mechanical inertia as it is far richer in contingent events having lasting consequences.