Species as Individuals in the Hierarchical Theory of Selection 599
(1982), Dawkins (1976, 1982), Eldredge (1985a), Fisher (1958), Ghiselin (1974a
and b), Leigh (1977), Lewontin (1970), Maynard Smith (1976), Stanley (1975,
1979), Vrba (1980; Gould and Vrba, 1982; Vrba and Gould, 1986), Williams
(1966, 1994), D. S. Wilson (1983), and Wright (1980). Collaborations between
philosophers and biologists have also added to the interest (for example, Wilson
and Sober, 1994; Sober and Wilson, 1998; Lloyd and Gould, 1993; Gould and
Lloyd, 1999).
Discussion of this most difficult and most important subject may be organized
in a hundred different ways. I have chosen a point of entry that may seem peculiar
or indulgent as an abstract philosophical question tenuously related to the "real"
biology of organic objects: are species individuals or classes? As a twofold
justification for this strategy, I found, first and personally, that I could best
organize this material and place all subjects into logical sequence, if I started here
and worked systematically outward through a particular net of implications.
(Others, no doubt, would choose different beginnings and construct just as sensible
and comprehensive a sequence.) Second and collectively, this particular
philosophical question has been widely and passionately discussed in the
biological literature, and has struck several scientists (e.g. Eldredge, 1995) as a
potential centerpiece unwisely relegated to a peculiar periphery by many scholars.
In 1974, Michael T. Ghiselin published an article in Systematic Zoology under
a title that I found insufferably self-indulgent at the time (especially since his
manuscript directly followed my own densely empirical article on local geographic
variation in the land snail Cerion bendalli on the Bahamian island of Abaco), but
have since come to view as adequately justified: "A radical solution to the species
problem." In short, Ghiselin argued that many classical problems about species
(not primarily or especially related to this chapter's topic of levels in selection)
could be instantly resolved if we—in the Pauline manner of "scales falling from
the eyes"—reversed our customary definition of species as classes (or universal
categories that can "house" objects) and reconceptualized them instead as
individuals (or particular things). A species then becomes a singular item—an
evolutionary entity defined by both a unique historical genesis and a current
particular cohesion.
I will not trace the large and complex trail that Ghiselin's proposal generated
in the scientific and philosophical literature (see, for example, Ghiselin, 1987). In
my reading and understanding, I do not think that any clean resolution can be
stated, or even any consensus described. Perhaps we might best acknowledge, with
Mayr (1982a and b), that the term "species," as conventionally used and
understood, includes statements about both classes and individuals. In this sense,
the extensive discussion of Ghiselin's proposal sharpened our thinking, but
provided no closure.
In another sense, however, and following a common (largely sociological)
pathway in science, the explicit airing of such an interesting theme launched, or at
least impacted in major ways, a substantial set of theoretical issues, including two
of central importance to this book: the nature of evolution as a historical discipline,
and the definition of individuality as crucial to the "units