Biological Complexity: Beyond the Genome


Biological development, evolution and behaviour are enormously complex processes. For instance, morphogenesis involves the emergence of tiers of organization that are not deterministically entailed by lower‐scale components. Such extensional (space–time) complexity can be detected at the level of chromatin states, where topologies are constrained by higher‐order pathways involving entire chromosomes or the nucleus. Once established, chromatin conformations can become heritable in mitosis and meiosis. Deoxyribonucleic acid (DNA) encodings are thus contained in a framework of epigenetic information, the complexity of which increases during ontogeny. Intensional (process and change) complexity is also evident, where genomes are shaped by cellular operations. Language and new representations need to be developed for representing such phenomena, because current reductive approaches to explaining complex systems, although useful in guiding observations, have become conceptually misleading when extrapolated to ontology. The approach we propose for constructing that language derives from hierarchy theory, involving both classes of complexity.

Key Concepts

  • Biological systems can be modelled as hierarchies.

  • Extensional complexity involves small‐scale functions being embedded within and contextualized by larger‐scale forms.

  • Dynamical complexity results from processes at different scalar levels mutually constraining each other, even though they cannot directly interact because they proceed at very different rates.

  • Phenotype construction is morphogenetic, with each event dependent on preceding ones and contextualized by collateral ones.

  • Chromatin states are an example of higher‐order cellular properties constraining lower‐level genomic events.

  • The cellular phenotype determines the activity of the genome via a series of informational channels across several scalar levels.

  • Genome structure is constrained by higher‐order boundary conditions, which is a type of intensional complexity.

Keywords: complexity; development; epigenetics; genome; hierarchies


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Salthe, Stanley N, and von Sternberg, Richard(Sep 2009) Biological Complexity: Beyond the Genome. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0005886.pub2]