Heterochrony (= different time) is any change in the timing of development in an animal or plant. It is a key concept in developmental biology and evolution, introduced by Ernst Haeckel in 1875. It applies to the time a trait appears in the growth of an organism, or to the timing of gene expression in development.
Its importance in biology is to explain the way closely related animals may come to have quite large differences in shape, and size, whilst nevetheless having a rather similar genome. The main components are the time a process starts and stops in development, and the rate at which the process works.
- Paedomorphosis: a change in the genotype so the adults of a species retain traits previously seen only in juveniles.
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