Evolutionary Transitions in Heritability and Individuality

Abstract

An evolutionary transition in individuality is de ned as the emergence of higher-level individuals from the interaction of lower-level ones during evolution. To occur, it requires both a process of natural selection at the higher (collective) level and heritability of traits at that level. Much of the literature on evolutionary transitions in individuality has focused on collective-level selection with some authors calling for a similar work to be carried out with respect to collective-level heritability. Starting from a model akin to Wilson's trait-group model I provide such an analysis. I show rst that when a collective trait is a linear function of the lower (particle) level trait, collective-level heritability is a by-product of particle-level heritability. It is equal to particle-level heritability, whether the particles interact randomly or not to form collectives. Second, one e ect of population structure is the reduction in variance of o spring collective-level character for a given parental collective. I argue that this reduction in variance is one dimension of individuality. Third, when collective-level characters are not linear functions of particle composition, collective-level heritability is not only low but also depends highly on the frequency of the di erent types of particles in the global population. Finally, population structure, because it can reduce the variance in o spring collective-level character, permits to increase collective-level heritability of such traits. In doing so, it also leads collective heritability to depend less on the frequencies of di erence type of particles than when population structure is low or absent.

Eco-evolutionary dynamics of nested Darwinian populations and the emergence of community-level heredity

“…There are two aspects to heredity: resemblance -the extent to which reproduction and development maintain the average offspring phenotype -and fidelity (or determination) -a measure of its variance (Jacquard, 1983;Bourrat, 2017). In our model, resemblance is established once density-dependent interactions counter the bias toward fast replicating particles: when the G function has an internal fixed point in φ, systematic drift of average collective colour is prevented.…”

Eco-evolutionary dynamics of nested Darwinian populations and the emergence of community-level heredity

“…There are two aspects to heredity: resemblance -the extent to which reproduction and development maintain the average offspring phenotype -and fidelity (or determination) -a measure of phenotypic variance (Jacquard, 1983;Bourrat, 2017). In our model, resemblance is established once density-dependent interactions counter the bias toward fast replicating particles: when the function has an internal fixed point in̂ , systematic drift of average collective colour is prevented.…”