The tacit standard view that development ends once reproductive capacity is acquired (reproductive boundary, or ‘‘RB,’’ thesis) has recently been challenged by biologists and philosophers of biology arguing that development continues until death (death boundary, or ‘‘DB,’’ thesis). The relevance of these two theses is difficult to assess because the fact that there is no precise definition of development makes the determination of its temporal boundaries problematic. Taking into account this difficulty, this article tries to develop a new species-dependent perspective (...) on temporal boundaries of development. This species-dependent account stands against both RB and DB theses since neither of them reflects the differences between species in the temporality of their development. In this perspective, I propose to use stem cells as a tool to analyze (1) the different developmental capacities of an organism during its life; and (2) the different developmental temporal capacities between species. In particular, I will show that stem cells enable four distinct temporal developmental patterns to be distinguished, i.e., four distinct temporal boundaries of development in the living. I show how these four patterns can be interpreted differently depending on the perspective one has on the definition of development. (shrink)

A great deal of progress has recently been made in characterizing the “mechanisms of aging.” A comparison with the mechanisms of development shows that the two sets of mechanisms are different; nevertheless, mechanisms of aging are conditioned by what happens during development. Aging and development also share some characteristics, such as a similar difficulty in attributing a precise temporal boundary to these processes. Other characteristics seem more specific to aging, such as the role of external (to the organism) and stochastic (...) events in its progression. In fact, both development and aging are historical processes with a mixture of stochastic events and deterministic processes, the ratio of the two being different in each process. Therefore, it is concluded that aging does not fit with a broad, lifelong conception of development. (shrink)

Regeneration capabilities are found in most or all animals. Whether regeneration is part of the development of an animal or a distinct phenomenon independent of development is a debatable question. If we consider regeneration as a process belonging to development, similarly to embryogenesis or metamorphosis, the existence of regenerative capabilities in adults can be seen as an argument in favor of the theory that development continues throughout the life of animals. Here I perform a comparative analysis of regeneration versus “classical” (...) developmental processes in animals in order to determine to what extent these processes are inclusive or distinct. I identify the existence of regeneration-specific processes, i.e., processes that occur during the regeneration, but not the initial development, of a given structure. In addition, I find that seemingly similar processes acting during development and regeneration may have differential molecular and cellular bases. I thus conclude that there are significant differences between regeneration processes in adult animals and developmental processes occurring during earlier phases of the life cycle. The existence of regenerative capabilities in adult animals can therefore not be used as an argument in favor of the idea that development spans the whole life. (shrink)

This special issue of Biological Theory is focused on development; it raises the problem of the temporal and spatial boundaries of development. From a temporal point of view, when does development start and stop? From a spatial point of view, what is it exactly that "develops", and is it possible to delineate clearly the developing entity? This issue explores the possible answers to these questions, and thus sheds light on the definition of development itself.