Perspective: Genetic Assimilation and a Possible Evolutionary Paradox: Can Macroevolution Sometimes Be So Fast as to Pass Us By?

Abstract

The idea of genetic assimilation, that environmentally induced phenotypes may become genetically fixed and no longer require the original environmental stimulus, has had varied success through time in evolutionary biology research. Proposed by Waddington in the 1940s, it became an area of active empirical research mostly thanks to the efforts of its inventor and his collaborators. It was then attacked as of minor importance during the "hardening" of the neo-Darwinian synthesis and was relegated to a secondary role for decades. Recently, several papers have appeared, mostly independently of each other, to explore the likelihood of genetic assimilation as a biological phenomenon and its potential importance to our understanding of evolution. In this article we briefly trace the history of the concept and then discuss theoretical models that have newly employed genetic assimilation in a variety of contexts. We propose a typical scenario of evolution of genetic assimilation via an intermediate stage of phenotypic plasticity and present potential examples of the same. We also discuss a conceptual map of current and future lines of research aimed at exploring the actual relevance of genetic assimilation for evolutionary biology.

Developmental plasticity mirrors differences among taxa in spadefoot toads linking plasticity and diversity

“…Although we agree with this observation, genetic assimilation, which is a special case of genetic accommodation (4), involves an initially plastic trait (environmentally induced) that becomes canalized or genetically fixed (4,9,16). In nature, a plastic trait may very likely retain a certain level of plasticity even after directional selection (10,22) because some environmental heterogeneity will most likely persist, resulting in a shifted, rather than a flat, reaction norm. Indeed, in our study system, even though the larval period has diverged remarkably among lineages, all species have maintained a substantial level of plasticity in the duration of the larval period (Fig.…”

“…This developmental plasticity may buffer the effects of environmental variation and slow down the genetic response to selection, thus retarding evolutionary change (4,6,7). However, plasticity may also promote evolutionary diversification if environmentally induced developmental variants allow populations to persist under different environments and subsequently diverge into independently evolving lineages (4,(8)(9)(10). For instance, phenotypic plasticity enables organisms to withstand environmental heterogeneity or invade new environments (11)(12)(13), potentially involving novel phenotypes.…”

Better with your parasites? Lessons for behavioural ecology from evolved dependence and conditionally helpful parasites

“…These changes become fixed (e.g. through genetic assimilation, Pigliucci & Murren, 2003) when (1) nearly all individuals in a population are infected by a parasite over many generations, (2) the number of parasites or their physiological impacts on their hosts is constant across generations, and (3) the costs of maintaining flexibility or plasticity outweigh the benefits in environments where parasites are always encountered.…”

“…through genetic assimilation, Pigliucci & Murren, 2003), and so the loss of parasites reduces the fitness of hosts that now accommodate infection with no benefit.…”

Grand challenges in evolutionary developmental biology

“…Under this broad umbrella, Waddington's (1953) genetic assimilation is the special case in which selection has favored the loss of plasticity (Robinson and Dukas, 1999;Pigliucci and Murren, 2003). The case in which plasticity enhances the survival of an individual in a new environment and selection subsequently favors heritable variation to accumulate in the direction of the plastic response, is currently known as the Baldwin effect (Baldwin, 1896; see also e.g., Crispo, 2007;Badyaev, 2009).…”