Heterochrony and Evolutionary Processes
Glossary
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Modern examples: Sexual Dimorphism K- and r- selection: Tertiary echinoids Consequences for debates on adaptation, constraints and evolutionary dynamics |
Phylogeny: The evolutionary history (i.e. descent) of an organism. Ontogeny: The developmental history of an organism. It was (and sometimes still is) thought that the two are related by... Recapitulation: During development, and organism passes through ("recapitulates") the adult forms of its ancestors. Ernst Haeckel held this to be a law of nature, which was referred to as the Biogenetic Law. Though not common, recapitulation does occur as a result of a more general process: Heterochrony: A process whereby morphological change is effectuated by relative changes in timing of developmental events, including the onset of maturity. As a result, descendants may not only recapitulate the adult forms of their ancestors, but the descendant adult may resemble the juvenile form of its ancestor. This is: Paedomorphosis: The retention of ancestral juvenile characters in the descendant. Descendants may as a whole appear like juvenile ancestors, or perhaps only a specific feature may appear like the analogous ancestral juvenile trait. This is, in essence, the converse of recapitulation, which is now referred to as: Peramorphosis: The occurance of ancestral adult characters in descendant juveniles. |
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As usual, there is a tendency to get carried away with terminology (jargon?). Don't worry about it: hopefully, the ideas behind studying heterochrony can be examined without having to wallow in technicalities. Continue navigating with the sidebar, or click here to continue with a foray into the historical antecedants of ideas about heterochrony. |
