Natural Selection and Causal Productivity - Mechanism and Causality in Biology and Economics - page 152

in the population, enhancing the survival of the population as a whole. Indeed, there
are many kinds of interactions among the members of the population. 11 Survival
interactions include direct physical combat; competition for limited food, sunlight,
or shelter resources; and cooperation, whereas reproductive interactions include
mating successfully or unsuccessfully and offspring rearing. Lots of interactions
imply that the organisms will share a common fate to a high degree.
To summarize, I have argued that populations, to a sufficient extent, are cate-
gorically individuals (objects) and are localized in space and time, that they do have
a stable structure, that they engage in activities as a unified entity, and that the
members of a population share a common fate. Thus, populations are not excluded
from being causally productive on that basis. But to make the positive case for
populations as causally productive, I return to Salmon's account of causal propaga-
tion, causal production, and the baseball example, which I use as an analogy.
5 Populations Can Be Causally Productive
First, like a baseball, a population is capable of transmitting a mark. For example, if
an organism in the population is born or killed, that “mark” persists in future states
of the population. However, Michael Strevens (personal communication) raises the
worry that if an organism disappearing from the population counts as a mark, then
Salmon's criterion will collapse. According to Strevens, Salmon wants to say, for
example, that a shadow traveling across a wall is not a causal process because
“marks” made on the shadow at one point (e.g., by a blemish on the wall) do not
persist to the next point - but the effect on a population of killing a member seems
very much like that (at one moment there, at the next moment not). Here I would
respond that, on my account, an organism is a member of a population in virtue of
the fact that it is interacting with other members of the population. So, if a new
organism is born, it will affect other organisms: eat their food, offer them some
food, mate with them, refuse to mate with them, etc. The population is changed
because of that new organism. So, when that organism later dies, the rest of
population is similarly affected - perhaps a small amount, but an effect nonetheless.
And since most organisms are more than just ephemeral shadows (let us suppose
most of them live more or less the average for the species), I think their appearance
and disappearance is different than the appearance and disappearance of a shadow.
The organisms persist, and thus, the mark on the population persists as well. That
being said, there are probably more obvious sorts of marks, such as a disease that
quickly spreads through a population, and, of course, all that really needs to be
11 The interactions within (or among) the members of a population are to be distinguished from the
interactions between the population as a whole and other entities. It is the occurrence of the former
interactions that binds the population together as a whole and thus makes possible the latter kinds
of interactions.