Heterochrony

Abstract

Heterochrony has often been proposed as a leading mechanism for macroevolutionary change in morphology of organisms, based simply on a relative shift in the timing of events during embryonic development in the evolving organisms. Its most recent formulation was in Gould's 'clock model'. Such timing shifts were seen as being controlled genetically (by 'rate genes') or by hormones (such as thyroxine). Heterochrony has much in common with the concept of allometry. The concept originated in the context of the idea of recapitulation where embryonic development was interpreted as a repetition of the organism's evolutionary history but in accelerated form; deviations from this recapitulation were identified as instances of heterochrony. In a later version used to explain macroevolutionary change (paedomorphosis), a new adult morphology is derived from ancestral larval forms by truncation of ancestral adult stages. However, it is difficult to see how genuine structural novelty can be explained, given that timing changes during development can in themselves do no more than redeploy preexisting characters. The explanatory value of the concept of heterochrony is increasingly questioned; at best it only indirectly relates to, or identifies, specific underlying mechanisms. It is in effect a form of redescription.

Evolution of Empathizing and Systemizing: Empathizing as an aspect of social intelligence, systemizing as an evolutionarily later consequence of economic specialization

“…(Neoteny is one type of the more general class of 'heterochrony' in which evolutionary change is brought about by alterations in the timing of developmental events; Horder, 2001. ) And this may provide a clue to the proximate mechanism for the evolution of higher levels of trait Systemizing.…”

Heterochronic genes in plant evolution and development

“…One explicit criticism is that heterochrony is unable to explain the origin of new structures in evolution, as only a shift in time of an existing process is meant by the term (Horder, 2013). However, the same criticism could be voiced against homeosis and heterotopy and relates more to the effect of the shift being dynamic or static (Webster and Zelditch, 2005).…”

Heterochrony and Morphological Variation of Epithalamic Asymmetry

“…It has also received criticisms for its weak explanatory power when used as an all‐encompassing concept. Thus, it is not surprising that many authors have devoted particular attention to the definition of heterochrony to remove ambiguities and contribute to a more rigorous approach (for discussion on this topic, refer to Smith, ; McNamara and McKinney, ; Horder, ; Hanken, ). In this article, we briefly review historical and conceptual aspects of heterochrony and bring our attention to the experimental considerations needed for a comprehensive analysis of this phenomenon.…”