• Morphological transitions often take place by changes in the rate, and timing, of developmental processes.

• A formerly popular idea - the principle of recapitulation - held that successive new evolutionary stages can only be added on to the adult stage; an individual then develops by 'climbing up its family tree'.

• In fact, new evolutionary stages may be added at any stage of an individual's development. The relative timing and rate of different developmental processes can also shift, in a process called heterochrony.

• The time of reproduction may be shifted earlier relative to somatic development (paedomorphosis) either because somatic development is slowed down (neoteny, e.g. the axolotl) or reproduction is accelerated (progenesis).

• Changes in the relative sizes of two organs can be studied by allometric graphs.

• Changes in complex shapes can be studied in D'Arcy Thompson's transformational diagrams.

• Goldschmidt, and his followers, have argued that developmental macromutations are the source of new large evolutionary changes: there is no evidence for this idea; and it is theoretically implausible, if not impossible.