Selection for Size, Shape, and Development Timing

First we examine the pairwise functional interrelations between size, shape, and the timing of development. Added to this well-known three-way relationship is a discussion of how selection can act on all three of these properties to effect quantitative changes in the others. One tentative conclusion is that there are many clear examples of selection acting on size and shape, and thence indirectly on timing; but examples of direct selection on timing tend to be either speculative or somewhat strained. The special case of metamorphosis, a qualitative change in form, is examined in the context of the quantitative triangle of time, shape, and size. Finally, we present a shopping list of important, unsolved problems.