parsimony/biology

[Kirk Fitzhugh]

Tom,

On the subject of things and events, things are involved in events, but
events themselves are not things. Nice discussions on these matters can be
found in Strawson's (1959) "Individuals," and in the writings of Wesley
Salmon on causality, and I think in Mahner & Bunge's (1997) "Foundations of
Biophilosophy." For instance, Strawson (1959: 46, original emphasis)
states, "Another distinction, worth mentioning now, to which I shall later
refer is that between, e.g., events and processes which, as named and
conceived of by us, necessarily are *of*, or performed or undergone *by*,
material bodies or things possessing material bodies, and events and
processes not of this kind."

If we do agree that cladograms are statements of initial causal conditions
that account for observed shared similarities, then cladograms do
hypothesize the past existence of individuals, in the form of organisms in
ancestral species. Cladograms also indicate that those individuals were
involved in events, such as speciation. That it is the case that events do
not have the ontological qualities of things, but denote the changes in
things over time, a monophyletic taxon, as indicated from a cladogram,
cannot be a thing as well. Monophyletic taxa are instances of causal
events, which places them in the realm of classes, not individuals. A very
good exposition on the nature of individuals can be found in Gracia's
(1988), "Individuality." I consider the same argument to apply to species,
which are instances of hybridization events (or asexual reproductive events
as the case might be). Taxa do not have the quality of non-instantiability,
which is the hallmark of individuality. Again, if a cladogram is to be
construed as an explanation for what we observe, which are the properties
of organisms, then taxa derived from cladograms represent instances from a
class of events.

You mention that "In the process of defining characters we percieve
patterns of shared properties amongst individual organisms." Actually, the
act of "defining" a character starts at the point of observing just a
single instance. There is no requirement that one name a property only
after seeing n+1 instances. That there is a pattern is already entailed
with the proposition, "individuals A and B both have property x."

You then say that, "In a further stage of character definition, we infer
that these shared properties are homologies - they are the "same" things,
present as a result of descent from a common ancestor." This is not a
"further stage" for defining a property. The same properties in A and B are
already firmly established at the point of having the perceptual belief
that x manifests itself in A and B. The following act of inferring a
homology hypothesis is to causally account for the existence of property x
in A and B outside of my mind. There is a clear distinction to be made
between the existence of properties of things and the inference of possible
explanations for the existence of those properties.

Your conclusion is that, "In other words we see a pattern amongst things
which we recognize as the various manifestations of a single historical
'thing'." This is only possible insofar as stating that from a causal
standpoint A and B exhibit the same properties because they are derived
from a common ancestor with that property. The only historical things to be
referred to are the individuals of that ancestral species that also had
property x prior to some speciation event. There are no other "individuals"
to be considered, species, genera, families, or otherwise. Reference to a
common ancestral species cannot be reference to a thing, but a set of
individual organisms that existed in the past that were involved in
hybridization events. If we pooled 100 people into a room, we would not say
we have "an individual" simply because all of them are derived from some
ancestral species. We recognize those 100 individuals as part of the same
species only because we infer their existence is due to a series of causal
events. Making the clear distinction between individuals and the fact that
events involve individuals, but are not themselves individuals, makes it
very clear how to refer to the causal aspects of cladograms and taxa.

Kirk