Major evolutionary transitions in individuality

Abstract

The evolution of life on earth has been driven by a small number of major evolutionary transitions. These transitions have been characterized by individuals that could previously replicate independently, cooperating to form a new, more complex life form. For example, archaea and eubacteria formed eukaryotic cells, and cells formed multicellular organisms. However, not all cooperative groups are en route to major transitions. How can we explain why major evolutionary transitions have or haven't taken place on different branches of the tree of life? We break down major transitions into two steps: the formation of a cooperative group and the transformation of that group into an integrated entity. We show how these steps require cooperation, division of labor, communication, mutual dependence, and negligible within-group conflict. We find that certain ecological conditions and the ways in which groups form have played recurrent roles in driving multiple transitions. In contrast, we find that other factors have played relatively minor roles at many key points, such as within-group kin discrimination and mechanisms to actively repress competition. More generally, by identifying the small number of factors that have driven major transitions, we provide a simpler and more unified description of how life on earth has evolved.T he evolution of life, from simple organic compounds in a primordial soup to the amazing diversity of contemporary organisms, has taken roughly 3.5 billion years. How can we explain the evolution of increasingly complex organisms over this period? A traditional approach has been to consider the succession of taxonomic groups, such as the age of fishes giving rise to the age of amphibians, which gave way to the age of reptiles, and so on. Although this approach has some uses, it is biased toward relatively large plants and animals and lacks a conceptual or predictive framework, in that it suggests we look for different explanations for each succession (1).Twenty years ago, Maynard Smith and Szathmáry (2) revolutionized our understanding of life on earth by showing how the key steps in the evolution of life on earth had been driven by a small number of "major evolutionary transitions." In each transition, a group of individuals that could previously replicate independently cooperate to form a new, more complex life form. For example, genes cooperated to form genomes, archaea and eubacteria formed eukaryotic cells, and cells cooperated to form multicellular organisms (Table 1).The major transitions approach provides a conceptual framework that facilitates comparison across pivotal moments in the history of life (2, 3). It suggests that the same problem arises at each transition: How are the potentially selfish interests of individuals overcome to form mutually dependent cooperative groups? We can then ask whether there are any similarities across transitions in the answers to this problem. Consequently, rather than looking for different explanations for the succession of different taxonomic groups, we ...

How Can Evolution Learn?

“…Here, we are particularly interested in the evolution of ecological relationships that change the co-selection of species (analogue of unsupervised correlation learning) [69]. Evo-ego: the evolution of Darwinian individuality [70][71][72][73][74]83]. We propose the term 'evo-ego' [34] to refer to the evolution of organisations (reproductive structures) that change the evolutionary unit -i.e., the level of biological organisation that exhibits heritable variation in reproductive success [40].…”

Darwin's aliens

“…Major transitions involve organisms cooperating so completely that they give up their status as individuals, becoming parts of a whole (Queller & Strassmann 2009). Unsurprisingly, then, major transitions require the extreme condition of effectively complete or perfect alignment of interests (Gardner & Grafen 2009;West et al 2015).…”

“…Under natural selection, units are selected to be selfish, striving to replicate themselves at the expense of others. Theory tells us that for units to unite under a common purpose, the evolutionary conflict between them must effectively eliminate (Gardner & Grafen 2009;West et al 2015).…”

“…Evolutionary theory has been used to explain a wide range of features of life on the Earth, from behaviour to morphology. For example, it has allowed us to predict when some organisms, especially insects, should manipulate the sex of their offspring, to produce an excess of sons or daughters, how some birds should forage for food, and why males tend to be larger than females (Darwin 1871;Clutton-Brock & Harvey 1977;Davies & Houston 1981;West 2009;Davies et al 2012). If life arises on other planets, then the evolutionary theory should be able to make similar predictions about it.…”

Inclusive Fitness Theory and the Evolution of Mind and Language

“…Hence communications between cells resulted in a division of labour (epigenesis resulted in several organs executing different functions) and, subsequently, gave rise to organ systems, such as the immune system involved in the defence against pathogens, or the endocrine and nervous system regulating our metabolism and behaviour. From an evolutionary point of view, the relevant division of labour was the separation between nonreproductive somatic cells and the reproductive cells or gametes (see Michod 2007;West et al 2015). This division of labour is explained by inclusive fitness theory in terms of altruism.…”