Two Senses of Individuality

Posted on November 2, 2015 by

Recently, David Wallace-Wells published “Adventures in the Science of the Superorganism” found here. He uses impressive examples to motivate the problem of biological individuality, such as one twin ingesting the embryo of the other twin in utero, the trillions of gut bacteria that house themselves within us, viruses and diseases that colonize our DNA, and the ever-so-strange fetus-in-fetu cases that are only fitting with Hallowe’en right around the corner. What is at stake here, according to Wallace-Wells, is reconciling our own personal individuality as humans with the notion that humans are superorganisms; these strange amalgamations of multiple and often genetically diverse biological entities. As humans, he claims, a large number of ‘selfs’ both human and non-human determine who we are, which yields a mosaic identity.

The general content of the article stems from an area in philosophy of biology that worries about how to individuate biological entities. The question of biological individuality mostly concerns how to carve up the organic world, rather than concerns about what constitutes a rich sense of individuality as a unique human self-identity.  That is, if we accept Lewontin’s (1970) view that natural selection acts on individuals, then what exactly is the nature of individuals in selection?  Some common sense criteria for individuality are the following:  Perhaps an individual should be spatially contiguous and, therefore, not persisting across different places in space at the same time.  Or maybe within those single borders the individual needs to physiologically unified in some sense with parts that work together to sustain the whole system.  Or perhaps an individual should be genetically homogenous without multiple genomes within its borders, or in the very least possess a unique genetic identity.

But consider the case of Armillaria ostoyae. Also known as the ‘humongous fungus,’ A. ostoyae spreads clonally underground.  In eastern Oregon, the fungi cluster into groups which are comprised of isolates (or clones).  They are genetically identical to other fungi groupings separated by large forests.  Those groups can spread out for up to 965 hectares (see Worrall et al.  2004).  It was previously thought the groups were individually discrete fungi until their genetic identity was established—all groupings had the same genotype.  So is this one individual organism or many?  If genetic homogeneity (or sameness) is the marker of individuality, then we should count all genetically identical groups of the fungus as one biological individual.  That is one very large individual organism!  However, this violates the intuition that individuals should at least be together in one place.

Symbiotic relationships cause similar problems for individuality. Symbionts are collectives of entities that are genetically different, but often work together in a way that is evolutionarily advantageous for both parties.  The Hawaiian BobTail squid along with Vibrio fischeri bacteria form a relationship of this kind.  The squid ingests the bacteria at night, then vents the bacteria during the day.  The luminescent properties of the bacteria help the squid to avoid predators.  Conversely, it appears as though certain strains of the bacteria have very specific relationships with different squids in a way that helps with their ability to survive (see Nishiguchi 2002).  This mutual relationship yields evolutionary benefits for both parties and if we accept that natural selection takes individuals as its target, then selection appears to act at the level of the squid-Vibrio as a whole.  Does this mean that the squid-Vibrio is an individual?  Not only do both parties disentangle themselves daily, they are also genetically distinct entities from very different branches on the tree of life and different bacteria strains can pair up with different squids.  To call the squid-Vibrio an individual seems strange indeed!

The interesting features of human cases that Wallace-Wells describes (mentioned above) are further instances of the individuality problem in philosophy of biology. Different philosophers give different sets of criteria for what it takes to be an individual.  But often counterexamples, such as the humongous fungus, squid-Vibrio, and human gut flora all create problems as we’ve seen.  The aim of the article seems much different though when compared to what philosophers of biology discuss when they worry about the nature of individuals in evolutionary theory.   Wallace-Wells is concerned about a richer sense of individuality akin to something like the notion of our unique identity as human individuality.  The existence of problematic cases allegedly threatens that rich sense of unique human individuality.  But does it really?  To think the threat is real is to assume that the richer notion of individuality somehow hinges on a much plainer sense of individuality, namely, the carving of nature into basic units and problems associated with that individuation.  I’m skeptical of the connection between the two senses of individuality, but I also tend not to worry about what makes humans special.  To take a Hull-inspired line of reasoning, we are human in so far as we are part of the human lineage.  To go further into human identity with ‘special-ness’ overtones is no matter to me, at least insofar as the individuality knife cuts.