Nascent life cycles and the emergence of higher-level individuality. (5th December 2017)

• Record Type: Journal Article
• Authors: Ratcliff, William C.; Herron, Matthew; Conlin, Peter L.; Libby, Eric
• Is Part Of: Philosophical transactions. Volume 372:Number 1735(2017)
• Publication Date: 2017-12-05
• Subjects: major transitions -- innovation -- cooperation -- division of labour -- complexity; Biology -- Periodicals; Science -- Periodicals; 570
• DOI: 10.1098/rstb.2016.0420
• Languages: English
• ISSNs: 0962-8436

Abstract

Abstract : Evolutionary transitions in individuality (ETIs) occur when formerly autonomous organisms evolve to become parts of a new, 'higher-level' organism. One of the first major hurdles that must be overcome during an ETI is the emergence of Darwinian evolvability in the higher-level entity (e.g. a multicellular group), and the loss of Darwinian autonomy in the lower-level units (e.g. individual cells). Here, we examine how simple higher-level life cycles are a key innovation during an ETI, allowing this transfer of fitness to occur 'for free'. Specifically, we show how novel life cycles can arise and lead to the origin of higher-level individuals by (i) mitigating conflicts between levels of selection, (ii) engendering the expression of heritable higher-level traits and (iii) allowing selection to efficiently act on these emergent higher-level traits. Further, we compute how canonical early life cycles vary in their ability to fix beneficial mutations via mathematical modelling. Life cycles that lack a persistent lower-level stage and develop clonally are far more likely to fix 'ratcheting' mutations that limit evolutionary reversion to the pre-ETI state. By stabilizing the fragile first steps of an evolutionary transition in individuality, nascent higher-level life cycles may play a crucial role in the origin of complex life. This article is part of the themed issue 'Process and pattern in innovations from cells to societies'.