Changes in the relative timing of development of different aspects of organisms.

Note that this is a relative term. That is, "change" must occur from a state that where change has not yet occurred. In practice, however, one tends to compare the development of from one species to that of another, particularly another that is fairly closely .

The result of heterochrony often is either the diminishment or exaggeration of a particular character relative to the rest of an organism. Consistently it can refer to either the acceleration or delay in achieving such that, for example, the organisms presents a relatively state as an , a phenomenon more specifically described as paedomorphosis.

An example is the of in comparison to their (presumably) -like ancestors. See also the concept of as well as as well as and .