Lane DesAutels (Missouri Western State University), Caleb Hazelwood (Georgia State University)
Individuals are things you can refer to, point to, and single out. In much of life science, individuality is indispensable for comparing, counting, and characterizing objects of study. But in the philosophy of life science, few authors can seem to agree what makes something a biological individual.
In recent literature (e.g., especially Godfrey-Smith 2013 and Pradeu 2016), philosophers have pointed to two independently fruitful categorizations that do not always coextend: biological individuality understood by appeal to physiology, and biological individuality understood in terms of evolution by natural selection. Put roughly, physiological individuals are biological entities characterized by a functional or metabolic integration, and evolutionary individuals are biological entities characterized by their being “seen” by natural selection (Clarke 2011). On the latter way of thinking, biological entities are individuated if and only if they constitute a unit of selection, thereby satisfying Lewontin’s criteria of producing heritable variation and demonstrating differential fitness (Lewontin 1970).
Within the evolutionary camp, however, there is significant debate over what is required for the satisfaction of Lewontin’s criteria of heritable variation. Godfrey-Smith, for example, makes a compelling argument for identifying evolutionary individuals via clearly defined parent-offspring lineages and vertically transmitted traits, specifically through reproduction (Godfrey-Smith 2013).
The trouble with Godfrey-Smith’s commitment to heredity understood in terms of clearly identifiable parent-offspring lineages and strict, obligate vertical transmission is that, in accepting this criterion, we must further accept that there are many instances where perfectly good physiological individuals are not evolutionary individuals. For example, any of the vast number of host-microbial symbiont associations, referred to as 'holobionts', would have to be dismissed on these grounds. This is because many holobiont hosts inherit their microbiome in large part through horizontal transmission, i.e., from the environment. Thus, on Godfrey-Smith’s characterization, they are not considered to possess evolutionary individuality. I call this the holobiont problem for evolutionary individuality.
This poster argues that, in pursuing a proper conception of evolutionary individuality, limiting the scope of heredity to reproduction fails to account for the ubiquity of horizontal transmission of adaptations in nature that play an important evolutionary role. In doing so, I aim to contribute to the development of a pluralistic account of evolutionary individuality that recognizes the myriad extra-genetic means of inheritance. I further contend that the Extended Evolutionary Synthesis (EES) may assist in such a development. In particular, I focus on one of the central notions developed in the EES literature: ecological inheritance understood via the mechanism of niche construction (Odling-Smee, Laland, & Feldman 2003). Ecological inheritance through niche construction is the process of heredity “through which previous generations as well as current neighbors can affect organisms by altering the external environment or niche that they experience” (Lamm 2012). I will argue that, through a horizontal transmission of microbial symbionts, holobionts partake in niche construction in a significantly heritable way, thus granting them some degree of evolutionary individuality. Having established this claim, I conclude, is sufficient for dismantling the holobiont problem for evolutionary individuality.
