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13

The Development of the

Philosophy of Species

There are two major questions about the analysis of the species category: First,

to what general ontological category do species taxa belong? Second, what

distinguishes species taxa from other members of this category?

Philip Kitcher^1

All philosophical arguments have antecedents, and all special topics (such as the
species problem) are broadly influenced by philosophical ideas and arguments from
outside the specialty in which they occur. This is equally true for the philosophy of
biology, and multiple resources are employed from the three broad areas of philo-
sophical enquiry.
Scientists, especially of recent decades, however, are often not so comfortable with
philosophical treatments of their specialty. For instance, Van Valen argued that the
resources of philosophy (at the time he wrote) are not really fit for the problem of species,
and lists the heterogeneous criteria that working taxonomists use to identify a species:

First, though, it may be useful to list some properties which, I trust, most biologists

agree apply to most species:

(1) A single origin and final extinction, with reproductive (informational) conti-
nuity between these events.
(2) Origin taking many, rather than several or one, generations.
(3) Limited but real extension in both time and space.
(4) Origin by transformation of a population of individuals, not from one or two
parents.
(5) Capacity to evolve.
(6) Capacity to act as a unit in evolution.
(7) Occurrence in spatially disjunct populations.
(8) Potential reproductive continuity among all included populations; compat-
ibility for development and fitness of offspring as well as for mating and
fertilization.
(9) A mechanism for recognizing other individuals or gametes of the same
species.
(10) Reproductive isolation from other species.
(11) Being composed of individuals.
(12) Capacity to speciate, either with or without phyletic branching.
(13) Capacity to remain the same species while, and after, part becomes another
species after phyletic branching.
(14) Possession of phenotypic, genic, and genotypic characters jointly distinct
from those of any other species.

(^1) Kitcher 1987, 185.