Linking a Biological Mechanism to Evolvability

Abstract

Evolvability has become a concept used to explain the common observation of clade asymmetry. However, the concept of evolvability means different things to different workers. Recent work has formalized the concept and we apply the formalized concept to a developmental system (primordial germ cell determination mechanism) that has been proposed to explain clade size disparity. In a simplified view, there are two general primordial germ cell (pgc) determination mechanisms: determinative and induced. The determinative mechanism is associated with species rich clades and the induced mechanism with species poor clades. The formal equations of evolvability provide a theoretical framework under which we can assess the relative influence of pgc determination mechanisms on clade evolvability. We propose that the determinative mechanism has enhanced evolvability in most clades that possess the trait.

Early usage and meaning of evolvability

“…This probabilistic framework allows the biologist to grasp relative probabilities of modification for specific traits or ecological influences in biotic systems. As illustrated by Crother and Murray (), specific developmental mechanisms applied to statements of evolvability allow for quantifiable relationships in evolutionary “ability” among clades, all else held constant.…”

“…All of these usages listed are similar, but subtly different, yet all involve either the capacity of populations to produce variation or simply the current variation present in a population at a given time, thus they all follow the Darwinian axiom that variation is required for evolution to occur, for example, “The capacity of populations to generate heritable phenotypic variation.” Since Brown (), the use of evolvability continued to subtly change. Crother and Murray (: 1) agreed with Brigandt () and considered evolvability as a process that appears to “enhance/increase the production of variation/novel traits” as seen in a relative context. Koonin and Wolf () even suggested that evolvability could be specific, biased, or even directed in a neo‐Lamarckian manner.…”

Andrew Johnson (1958-2021)

“…AJ and his co-workers reasoned that the evolution of any mechanism that enhances genetic diversity should be favored in a biological system (e.g. Crother and Murray, 2018). Because the net effect of germ plasm is an increase in heritable mutations, it would increase the phenotypic variation upon which selection can act to evolve novel traits.…”