Heterochrony

In biology, heterochrony is defined as a developmental change in the timing of events, leading to changes in size and shape. There are two main components, namely (i) the onset and offset of a particular process, and (ii) the rate at which the process operates. A developmental process in one species can only be described as heterochronic in relation to the same process in another species, considered the basal or ancestral state, which operates with different onset and/or offset times, and/or at different rates. The concept was first introduced by Haeckel in 1875ref|intro.

An example can best illustrate the concept. If a developmental process, such as the growth of a tail in the embryo of "species A", starts earlier and ends earlier than that of "species B", but the rate of growth is the same for both, the final result may basically be the same, although the tail of species A develops earlier than the one of species B.
If the onset and offset are unaffected, but the rate of growth is increased, the tail will be larger. If the offset is delayed and the rate is unaffected, the tail will be also larger. All possible combinations have been identified in living animals.

Heterochronies are easily identifiable when comparing phylogenetically close species, for example a group of different bird species whose legs differ in their average length.

Several heterochronies have been described in humans, relative to the chimpanzee. For instance, brain and head growth in the chimpanzee fetus starts at about the same developmental stage and present a growth rate similar to that of humans, but end soon after birth. Humans, on the contrary, continue their brain and head growth several years after birth. This particular type of heterochrony is named hypermorphosis and involves a delay in the offset of a developmental process, or what is the same, the presence of an early developmental process in later stages of development. Humans are known for presenting about 30 different neotenies in comparison to the chimpanzeeref|human.

References

# Horder, Tim (April 2006) Heterochrony. In: ENCYCLOPEDIA OF LIFE SCIENCES. John Wiley & Sons, Ltd: Chichester.
# See "Comparison of cranial ontogenetic trajectories among great apes and humans" by P. Mitteroecker et al in "Human Evolution" (2004) Volume 46, pages 679-697 Entrez Pubmed|15183670 and also "Ontogenetic study of the skull in modern humans and the common chimpanzees: neotenic hypothesis reconsidered with a tridimensional Procrustes analysis" by X. Penin, C. Berge and M. Baylac in "American Journal of Physical Anthropology" (2002) Volume 118, pages 50-62. Entrez Pubmed|11953945.

ee also

* Developmental biology
* Embryogenesis
* Evolutionary biology
* Neoteny
* Pedomorphosis
* Progenesis
* Phylogeny


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  • heterochrony — heterochrony. См. гетерохрония. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) …   Молекулярная биология и генетика. Толковый словарь.

  • Heterochrony — Heterochronism Het er*och ro*nism, Heterochrony Het er*och ro*ny, n. [Gr. ? of different times; ? other + ? time.] (Biol.) In evolution, a deviation from the typical sequence in the formation of organs or parts. [1913 Webster] …   The Collaborative International Dictionary of English

  • heterochrony — noun see heterochronism * * * heterochronic /het euhr euh kron ik/, heterochronistic, heterochronous, adj. /het euh rok reuh nee/, n. Biol. a genetic shift in timing of the development of a tissue or anatomical part, or in the onset of a… …   Useful english dictionary

  • heterochrony — Lack of synchronization …   Dictionary of molecular biology

  • heterochrony — heterochronic /het euhr euh kron ik/, heterochronistic, heterochronous, adj. /het euh rok reuh nee/, n. Biol. a genetic shift in timing of the development of a tissue or anatomical part, or in the onset of a physiological process, relative to an… …   Universalium

  • heterochrony — noun the variation in ontogeny of individuals of a species that gives rise to evolution …   Wiktionary

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  • heterochrony — het·er·och·ro·ny …   English syllables

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  • Ontogeny and Phylogeny (book) — Ontogeny and Phylogeny is Stephen Jay Gould s first technical book, published in 1977 by Belknap, a division of Harvard University Press. Gould wrote that Ernst Mayr suggested in passing that he write the book, but that I only began it as a… …   Wikipedia

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