Heterochrony facts for kids

Axolotls retain gills and fins as adults; these are juvenile features in most amphibians.

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.

Related terms

• Paedomorphosis: a change in the genotype so the adults of a species retain traits previously seen only in juveniles.
  • Neoteny: in which bodily development is slowed, but sexual development continues at the same rate. This results in a sexually mature juvenile or larval form. See Axolotl.
  • Progenesis: in which development is halted before full maturity.
  • Postdisplacement: in which the start of development is delayed.

Images for kids

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  Giraffes acquired their long necks through heterochrony, extending the development period of the seven neck vertebrae growth in the embryo to add length to the bones, not by adding more bones.

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  Despite greatly differing neck lengths, giraffes (right) have no more cervical vertebrae, just 7, than their fellow giraffids, okapi (left). With the number constrained, the development of the vertebrae is extended, allowing them to grow longer.

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  Irish elk skeleton with antlers spanning 2.7 metres (8.9 ft) and a mass of 40 kg (88 lb)

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  A 1901 comparison of a frog tadpole (a vertebrate) and a tunicate larva; in 1928 Walter Garstang proposed that vertebrates derived from such a larva by neoteny.

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  Neoteny in human development

See also

In Spanish: Heterocronía para niños