1280 THE STRUCTURE OF EVOLUTIONARY THEORY
their central status in revising and expanding evolutionary theory because they
represent the primary input of an overtly structuralist and nonadaptationist concept
into the central logic of evolutionary causation.
Choosing a fundamentum divisionis for taxonomy: an
apparently arcane and linguistic matter that actually embodies a
central scientific decision
Table 11-2 presents my sketchy and preliminary proposal for taxonomy of
subcategories in the exaptive pool. I shall retain franklins, or inherent potentials, as
an integrity for now, not because I doubt that they could be usefully divided into
subcategories, but simply because I wish to focus upon miltons, or available things,
as the component of the exaptive pool that holds most reformatory promise within
evolutionary theory.
I divide miltons into two major categories according to their different modalities
of generation: structurally, as automatic and nonadaptive sequelae or side
consequences of changes in other features, or at other levels; and historically, as
nonadaptive features not linked by structural or mechanical necessity to another
feature of a biological individual, but rather introduced sequentially in time by
processes that can generate and tolerate such nonadaptive entities.
I then divide each of these two subcategories into two further groups. Structural
miltons, as necessarily and automatically consequential, are all, and collectively,
spandrels. But spandrels come in two different "flavors," with the second group of
cross-level effects (newly so categorized here) representing, in my judgment, the key
addition that elevates spandrels to a position of central importance in evolutionary
theory. (I will present my full argument for considering cross-level effects as
spandrels in the next section, pp. 1286- 129 4.) In any case, the first structural group of
at-level, or architectural, spandrels includes the mechanical and automatic side
consequences, deployed throughout the rest of the individual, of any primary change
(usually adaptive) evolved by other features of the same individual. When I originally
defined the biological concept of spandrels (Gould and Lewontin,
Table 11-2. A Taxonomy for the Exaptive Pool