PSA2016: The 25th Biennial Meeting of the Philosophy of Science Association

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Biological Individuality and Pluralism: The Case of Holobionts

There are different ways to define biological individuality. Yet many of those accounts assume that an individual is a product of single genome and that genome belongs to a single species (Gilbert et al., 2012). I call this assumption the ‘received assumption’. In this poster, I explore the question of how should we understand a biological individual in light of holobiont research. Holobiont research emphasizes the symbiotic relationship between a host organism and its permanent microorganisms, and it forces us to reconsider traditional treatments of biological individuality (Dupre´ and O’Malley, 2012). I suggest that a host and its associated microorganisms should be considered an integrated unit. I argue that the received assumption offers a limited analysis because it does not adequately capture the nature of holobionts. I support this claim with three reasons. First, we need to invoke the idea of holobiont to explain some biological traits (e.g. traits which are related with human digestion). Second, natural selection does not always affect the host and its microorganism separately, but can act on whole holobionts as well. For instance, the symbiotic partnership between pea aphids and a bacterial species of Buchnera aphidicola can be considered as an example of holobiont-level selection (Booth, 2014). Third, considering holobionts as individuals could be beneficial in health issues. For example, we might need to conceive of a human infant as a holobiont to overcome medical conditions and to develop new treatment techniques (Gilbert 2014). For these reasons (and more) the received assumption that biological individuals are single species individuals does not work in all biological contexts. In addition to single species individuals there are multi-species individuals. Nevertheless, both the received assumption and the holobiont perspective can be helpful in particular contexts. Therefore, I favor a pluralistic approach to biological individuality. In other words, I argue that we should not buy the received assumption – the single species genome view - but a pluralistic approach to individuality that allows that there are single species genome individuals and multi species individuals.


Booth, A. (2014). Symbiosis, selection, and individuality. Biology & Philosophy, 29(5): 657–673.

Dupré J and O’Malley MA (2009). Varieties of living things: Life at the intersection of lineage and metabolism. Philosophy & Theory in Biology. 1: 1-24.

Gilbert, S.F., Sapp. J., and Tauber, A. I. (2012). A symbiotic view of life: We have never been individuals. Quarterly Review of Biology 87: 325 – 341

Gilbert, SF. (2014). A holobiont birth narrative: The epigenetic transmission of the human microbiome. Frontiers Genetics doi: 10.3389/fgene.2014.00282.

Author Information:

Sinan Sencan    
University of Calgary


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