The evolution of individuality revisited

Abstract

Evolutionary theory is formulated in terms of individuals that carry heritable information and are subject to selective pressures. However, individuality itself is a trait that had to evolve - an individual is not an indivisible entity, but a result of evolutionary processes that necessarily begin at the lower level of hierarchical organisation. Traditional approaches to biological individuality focus on cooperation and relatedness within a group, division of labour, policing mechanisms and strong selection at the higher level. Nevertheless, despite considerable theoretical progress in these areas, a full dynamical first-principles account of how new types of individuals arise is missing. To the extent that individuality is an emergent trait, the problem can be approached by recognising the importance of individuating mechanisms that are present from the very beginning of the transition, when only lower-level selection is acting. Here we review some of the most influential theoretical work on the role of individuating mechanisms in these transitions, and demonstrate how a lower-level, bottom-up evolutionary framework can be used to understand biological complexity involved in the origin of cellular life, early eukaryotic evolution, sexual life cycles and multicellular development. Some of these mechanisms inevitably stem from environmental constraints, population structure and ancestral life cycles. Others are unique to specific transitions - features of the natural history and biochemistry that are co-opted into conflict mediation. Identifying mechanisms of individuation that provide a coarse-grained description of the system's evolutionary dynamics is an important step towards understanding how biological complexity and hierarchical organisation evolves. In this way, individuality can be reconceptualised as an approximate model that with varying degrees of precision applies to a wide range of biological systems.

Inheritance is a Surjection: Description and Consequence

“…The mathematics that describes how biological evolution works began in the late 19th century, representing the frequency or relative frequencies of alternative alleles at specific loci. If we define a single species, there are common sets of DNA/RNA that define that single species, but there may also be recombination of the alleles that can act at each loci [5,6] made a similar observation. These variants may create features in specific offspring that are not determined by the common genes in all of that species.…”

“…When we say that the offspring of an evolutionary process are unique, we mean that there is at least one (but perhaps many) differences between each of those offspring. Radzevilavicius and Blackstone's [5] very detailed review of the evolution of individuality of offspring populations shows that all individuals, of all species, created by evolution are also in some form unique; the reader should see that article for its many details. Thus, the authors of reference [5] conclude "since [our review] … only relies on universal principles of life's evolution, this framework can potentially be applied to all life, no matter what its chemistry, and wherever it is found" (p. 1630).…”

Why Do Corals Bleach? Conflict and Conflict Mediation in a Host/Symbiont Community

“…Evolutionary conflict is an enduring theme in biology (Box ). In the last several decades, evolutionary theory has developed an increased appreciation for the causes and consequences of such conflict, particularly in the context of the history of life . While symbioses were once regarded as exceptions to “Darwinian” conflict, more recent research clearly supports the contrary view .…”

“…For instance, presence of a unicellular stage in the development of many multicellular organisms has been highlighted as a mechanism of conflict mediation . Increasingly, however, there is an appreciation that conflict mediation involves mechanisms co‐opted from idiosyncratic features of the underlying biology and biochemistry (Box ) …”

Does resource availability help determine the evolutionary route to multicellularity?

“…In contrast to the implications of Buss's theory of evolution and development through intra-individual selection (Buss, 1987;Radzvilavicius & Blackstone, 2018), multicellularity may be viewed as a facultative consequence of interactions between cells of the same or different genotypes, based largely on preadaptations (Nanjundiah, 2016): Multicellular development does not necessarily require monoclonality. Examples include, but are not limited to, polyclonal dictyostelids, polyembryonic insects, experimental intergeneric chimerism in fish and interspecific chimerism in mammals (Newman, 2014).…”