smith: organisms as persisters
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individuals, by suggesting that the
functions performed by microbiotic symbionts are apt for
selection.
This approach is too restrictive. Indeed, I agree with Theis that “one can look at holobionts
and hologenomes as incontrovertible realities of nature” (Theis et al. 2016, 2), the sort of realities
that need not be biological individuals. Douglas and Werren are committed to the view that
for a biological system to count as an entity it must be a biological individual, and for it to be a
biological individual it must be a unit of selection. But on my account, biological systems need
not be individuals in order to be biological entities. That is, systems can be entities by being
individuals, but they can also be entities by being organisms.
The analysis of organismality that I have presented in this paper shows that one can grant
that holobionts are not biological individuals while also granting that they—as functionally dif-
ferentiated and integrated persisters—are organisms. The claim that holobionts are “incontro-
vertible realities of nature” that are not units of selection is just the claim that they are organisms
but not biological individuals, and if we grant that organismality is a scientifically respectable
biological rank that is orthogonal to individuality this does not amount to throwing the baby out
with the bathwater. Furthermore, in light of the constitutively embedded character of organisms,
which implies that there is no precise line of demarcation between organisms and environments,
viewing holobionts as ecological communities of organisms does not rule out viewing them as
organisms. Recognizing that organisms are not free-floating and accepting the view that they
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