The only way to get from genotype to phenotype is via development. ~ American developmental biologist Scott Gilbert
Organismal development is an exercise in genetic control. Development is an interpretive process aligned with chemical conglomerations around DNA molecules. Development is also an ecological experience: cells interacting within an environmental context. From an evolutionary perspective, development (evo-devo) presents adaptive results from the experiences of prior generations.
Evolution does not produce novelties from scratch. It works on what already exists, either transforming a system to give it new functions or combining several systems to produce a more elaborate one. ~ François Jacob
Development transpires in a determined order and according to an exact schedule: a precise process of an organism transitioning from state to state. To differentiate “development” in early life from those experiences of “maturity” semantically obscures that living is always a series of state transitions. Development is defined by those youthful times when morphological changes are most pronounced.
Evolutionary innovations show themselves during development. Novelties may arise from deviations in the timing or position of gene expression (heterochrony and heterotopy), changes in growth rate (allometry), and/or alterations in other regulated events. Development derives from a coherent regulatory regime. Evolution emanates from tailoring the development regime.
Heterochrony is an evolutionary modification in the timing or rate of development events, leading to altered morphology. Neoteny – the retention of traits in adulthood of those only previously seen during development – is one kind of heterochrony. Animal domestication, such as seen in dogs, cats, and pigs, often results in neoteny.
Peramorphosis – delayed maturation with extended growth periods – is another type of heterochrony. The massive antlers of Irish elk resulted from peramorphosis.