Community hub
Recent from talks
Knowledge base stats:
Talk channels stats:
Members stats:
Heterochrony
In evolutionary developmental biology, heterochrony is any genetically controlled difference in the timing, rate, or duration of a developmental process in an organism compared to its ancestors or other organisms. This leads to changes in the size, shape, characteristics and even presence of certain organs and features. It is contrasted with heterotopy, a change in spatial positioning of some process in the embryo, which can also create morphological innovation. Heterochrony can be divided into intraspecific heterochrony, variation within a species, and interspecific heterochrony, phylogenetic variation, i.e. variation of a descendant species with respect to an ancestral species.
These changes all affect the start, end, rate or time span of a particular developmental process. The concept of heterochrony was introduced by Ernst Haeckel in 1875 and given its modern sense by Gavin de Beer in 1930.
The concept of heterochrony was introduced by the German zoologist Ernst Haeckel in 1875, where he used it to define deviations from recapitulation theory, which held that "ontogeny recapitulates phylogeny". As Stephen Jay Gould pointed out, Haeckel's term is now used in a sense contrary to his coinage; Haeckel had assumed that embryonic development (ontogeny) of "higher" animals recapitulated their ancestral development (phylogeny), as when mammal embryos have structures on the neck that resemble fish gills at one stage. This, in his view, necessarily compressed the earlier developmental stages, representing the ancestors, into a shorter time, meaning accelerated development. The ideal for Haeckel would be when the development of every part of an organism was thus accelerated, but he recognised that some organs could develop with displacements in position (heterotopy, another concept he originated) or time (heterochrony), as exceptions to his rule. He thus intended the term to mean a change in the timing of the embryonic development of one organ with respect to the rest of the same animal, whereas it is now used, following the work of the British evolutionary embryologist Gavin de Beer in 1930, to mean a change with respect to the development of the same organ in the animal's ancestors.
In 1928, the English embryologist Walter Garstang showed that tunicate larvae shared structures such as the notochord with adult vertebrates, and suggested that the vertebrates arose by paedomorphosis (neoteny) from such a larva. The proposal implied (if it were correct) a shared phylogeny of tunicates and vertebrates, and that heterochrony was a principal mechanism of evolutionary change.
Modern evolutionary developmental biology (evo-devo) studies the molecular genetics of development. It seeks to explain each step in the creation of an adult organism from an undifferentiated zygote in terms of the control of expression of one gene after another. Further, it relates such patterns of control of development to phylogeny. De Beer to some extent anticipated such late 20th-century science in his 1930 book Embryos and Ancestors, showing that evolution could occur by heterochrony, such as in paedomorphosis, the retention of juvenile features in the adult. De Beer argued that this enabled rapid evolutionary change, too brief to be recorded in the fossil record, and in effect explaining why apparent gaps were likely.
Heterochrony can be divided into intraspecific and interspecific types.
Intraspecific heterochrony means changes in the rate or timing of development within a species. For example, some individuals of the salamander species Ambystoma talpoideum delay the metamorphosis of the skull. Reilly and colleagues argue we can define these variant individuals as paedotypic (with truncated development relative to the ancestral condition), peratypic (with extended development relative to the ancestral condition), or isotypic (reaching the same ancestral shape, but via a different mechanism).
Interspecific heterochrony means differences in the rate or timing of a descendant species relative to its ancestor. This can result in either paedomorphosis (truncating the ancestral ontogeny), peramorphosis (extending past the ancestral ontogeny), or isomorphosis (reaching the same ancestral state via a different mechanism).
Hub AI
Heterochrony AI simulator
(@Heterochrony_simulator)
Heterochrony
In evolutionary developmental biology, heterochrony is any genetically controlled difference in the timing, rate, or duration of a developmental process in an organism compared to its ancestors or other organisms. This leads to changes in the size, shape, characteristics and even presence of certain organs and features. It is contrasted with heterotopy, a change in spatial positioning of some process in the embryo, which can also create morphological innovation. Heterochrony can be divided into intraspecific heterochrony, variation within a species, and interspecific heterochrony, phylogenetic variation, i.e. variation of a descendant species with respect to an ancestral species.
These changes all affect the start, end, rate or time span of a particular developmental process. The concept of heterochrony was introduced by Ernst Haeckel in 1875 and given its modern sense by Gavin de Beer in 1930.
The concept of heterochrony was introduced by the German zoologist Ernst Haeckel in 1875, where he used it to define deviations from recapitulation theory, which held that "ontogeny recapitulates phylogeny". As Stephen Jay Gould pointed out, Haeckel's term is now used in a sense contrary to his coinage; Haeckel had assumed that embryonic development (ontogeny) of "higher" animals recapitulated their ancestral development (phylogeny), as when mammal embryos have structures on the neck that resemble fish gills at one stage. This, in his view, necessarily compressed the earlier developmental stages, representing the ancestors, into a shorter time, meaning accelerated development. The ideal for Haeckel would be when the development of every part of an organism was thus accelerated, but he recognised that some organs could develop with displacements in position (heterotopy, another concept he originated) or time (heterochrony), as exceptions to his rule. He thus intended the term to mean a change in the timing of the embryonic development of one organ with respect to the rest of the same animal, whereas it is now used, following the work of the British evolutionary embryologist Gavin de Beer in 1930, to mean a change with respect to the development of the same organ in the animal's ancestors.
In 1928, the English embryologist Walter Garstang showed that tunicate larvae shared structures such as the notochord with adult vertebrates, and suggested that the vertebrates arose by paedomorphosis (neoteny) from such a larva. The proposal implied (if it were correct) a shared phylogeny of tunicates and vertebrates, and that heterochrony was a principal mechanism of evolutionary change.
Modern evolutionary developmental biology (evo-devo) studies the molecular genetics of development. It seeks to explain each step in the creation of an adult organism from an undifferentiated zygote in terms of the control of expression of one gene after another. Further, it relates such patterns of control of development to phylogeny. De Beer to some extent anticipated such late 20th-century science in his 1930 book Embryos and Ancestors, showing that evolution could occur by heterochrony, such as in paedomorphosis, the retention of juvenile features in the adult. De Beer argued that this enabled rapid evolutionary change, too brief to be recorded in the fossil record, and in effect explaining why apparent gaps were likely.
Heterochrony can be divided into intraspecific and interspecific types.
Intraspecific heterochrony means changes in the rate or timing of development within a species. For example, some individuals of the salamander species Ambystoma talpoideum delay the metamorphosis of the skull. Reilly and colleagues argue we can define these variant individuals as paedotypic (with truncated development relative to the ancestral condition), peratypic (with extended development relative to the ancestral condition), or isotypic (reaching the same ancestral shape, but via a different mechanism).
Interspecific heterochrony means differences in the rate or timing of a descendant species relative to its ancestor. This can result in either paedomorphosis (truncating the ancestral ontogeny), peramorphosis (extending past the ancestral ontogeny), or isomorphosis (reaching the same ancestral state via a different mechanism).