 Although reproduction itself has sometimes been conceptualized as part of the life cycle of biological individuals, the role of reproduction in intergenerational life cycles in general requires more careful articulation. For there are many species in which only a small minority of individuals actually get to reproduce, with reproductive skew being a widespread feature. Meanwhile it seems clear that all of these biological individuals, however much or little they reproduce, still possess a life cycle. Note that even the capacity to reproduce is not a universal feature of life cycles. This is not only because the capacity itself may not be replicated, but also because there are biological individuals designed by natural selection to be non-reproductive, with sterile castes in eusocial insects being perhaps the best-known example. 