Moorad et al  reinforces and elaborates on warnings made previously [2, 3] that Williams’ “hypothesis” should be treated with scepticism. A proper hypothesis should be based upon the best information available at the time, and for the case of the evolutionary theory of senescence, Hamilton’s model of selection is superior to Williams’. Hamilton’s insights improved over Williams’ by his appreciation for how fertility and juvenile survival schedules play a critical role in defining selection. While Williams’ model is not articulated mathematically, it is clear that his hypothesis is motivated by his belief that the strength of selection against mortality specific to some age follows from the frequency of individuals that survived to that age . However, Hamilton  was quite clear: the strength of selection is equal to the proportion of newborns that came from parents that survived to that age (see  or Equation 1 in the Appendix). Furthermore, Williams’ explicitly states that juvenile mortality cannot affect the evolution of senescence while Hamilton’s formulae show us that it can. It should be emphasized that Williams himself came to appreciate that Hamilton’s model describes the best way to think about how selection works [e.g., 6].