good introduction to punctuated equilibrium (Chapter 9, pp. 745-749). The largely
unknown paradox of Lankester's original definition of homoplasy as a category of
homology, rather than in the opposite status held by the term today, provides the
best entry I could devise for understanding the vital, but little appreciated and
rarely acknowledged, theoretical differences between parallelism and convergence.
In the absence of this context and distinction, the key importance of evo-devo and
the discovery of deep homology among distant phyla cannot properly be grasped
as a challenge and expansion of Darwinian expectations (Chapter 10).
I hope that my sympathetic portrayal of D'Arcy Thompson's theory of form
(Chapter 11), despite my general disagreement with his argument, will help
colleagues to understand the thrust and potential power of this unusual formulation
of structuralist constraint on external grounds of universal physics. Although I am
chagrined that I discovered Nietzsche's account of the distinction between current
utility and historical origin so late in my work, I know no better introduction—
from one of history's greatest philosophers to boot, and in his analysis of morality,
not of any scientific subject—to the theoretical importance of spandrels and
exaptation in the rebalancing of constraint and adaptation within evolutionary
theory (Chapter 11, pp. 1214-1218). In a final historical analysis of the second part,
I think that Darwin's own rationale for progress (Chapter 12, pp. 1296-1303),
rooted not in the mechanics of natural selection itself, but in an ecological
argument for extrapolation of biotic competition through time in a perpetually
crowded world—an aspect of Darwin's thought that has very rarely been
appreciated, formulated or discussed by historians—provided the best context I
could devise for understanding why catastrophic mass extinction in particular, and
non-extrapolation through tiers of time in general, play such havoc with Darwin's
need for uniformity on the third branch of his essential logic.
The original claims in the book's second half on modern reformulations of
evolutionary theory rest, necessarily and primarily, on theoretical insights and
unusual conceptual parsings, rather than on novel data—if only because custom
dictates that my extensive empirical documentation be presented in "review"
format by collating published studies in support or refutation of general themes
under discussion. But I have sometimes presented existing data in novel contexts—
as in my analysis of the proper category for understanding the exaptive value of
genes lost by founder drift in establishing the social cohesion (albeit transient) that
has made the Argentine ant Linepithema humile such a successful invader of non-
native Californian habitats (Chapter 11, pp. 1282-1284). I have also cited my own
empirical studies, previously published but original in the more conventional
sense, to support important pieces of more general arguments, including validation
of punctuated equilibrium by dissection of a single bedding plane to reveal
transition by absolute age dating of individual shells (Goodfriend and Gould,
1996), the "employment" of constraint by selection to yield several adaptive
features by one heterochronic change in a case of neoteny in Gryphaea (Jones and
Gould, 1999), and the explanation of most ordered geographic variation within
Defining and Revising the Structure of Evolutionary Theory 53