FACTOID # 25: If you're tired of sitting in traffic on your way to work, move to North Dakota.
 
 Home   Encyclopedia   Statistics   States A-Z   Flags   Maps   FAQ   About 
   
 
WHAT'S NEW
 

SEARCH ALL

FACTS & STATISTICS    Advanced view

Search encyclopedia, statistics and forums:

 

 

(* = Graphable)

 

 


Encyclopedia > 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. Main articles: Life All organisms (viruses not included) consist of cells, which in turn, are based on a common carbon-based biochemistry. ... In biology, a species is, loosely speaking, a group of related organisms that share a more or less distinctive form and are capable of interbreeding. ... In biology, a species is, loosely speaking, a group of related organisms that share a more or less distinctive form and are capable of interbreeding. ... An ancestor is a parent or (recursively) the parent of an ancestor. ...


An example can best illustrate the concept. If a developmental process such as the growth of a tail in the embryo of "species A" of a salamander starts earlier and ends earlier, at the same rate, than that of "species B", although the tail of the animal will be developed earlier in development the final result may be basically the same. 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 identifyable 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 neoteny 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 chimpanzee[1]. Type species Simia troglodytes Blumenbach, 1775 Species Pan troglodytes Pan paniscus Chimpanzee, often abbreviated to chimp, is the common name for two species in the genus Pan. ... Fetus at eight weeks A fetus (alternatively foetus or fœtus) is an unborn vertebrate offspring after the embryonary stage. ... Neoteny is a term in developmental biology that describes the retention of juvenile characteristics in the adults of a species and is similar to but not the same as progenesis, which is the attainment of sexual maturity by an organism still in its larval stage, as is found among certain...


It is an idea that is strongly based in evolutionary biology and embryology. Evolutionary biology is a subfield of biology concerned with the origin and descent of species, as well as their change over time, i. ... Embryology is the subdivision of developmental biology that studies embryos and their development. ...


References

  1. ^  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.

The Entrez Global Query Cross-Database Search System allows access to databases at the National Center for Biotechnology Information (NCBI) website. ... The Entrez Global Query Cross-Database Search System allows access to databases at the National Center for Biotechnology Information (NCBI) website. ...

See also


  Results from FactBites:
 
Heterochrony - Wikipedia, the free encyclopedia (374 words)
In biology, heterochrony is defined as a developmental change in the timing of events, leading to changes in size and shape.
Heterochronies are easily identifyable when comparing phylogenetically close species, for example a group of different bird species whose legs differ in their average length.
This particular type of heterochrony is named neoteny 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.
  More results at FactBites »

 
 

COMMENTARY     


Share your thoughts, questions and commentary here
Your name
Your comments

Want to know more?
Search encyclopedia, statistics and forums:

 


Press Releases |  Feeds | Contact
The Wikipedia article included on this page is licensed under the GFDL.
Images may be subject to relevant owners' copyright.
All other elements are (c) copyright NationMaster.com 2003-5. All Rights Reserved.
Usage implies agreement with terms, 1022, m