224 THE STRUCTURE OF EVOLUTIONARY THEORY
eventual judgment about merit and utility. Weismann, by far the most thoughtful of
Darwinians in the first generation after the founder himself, could not "cash out"
the exclusivity of organismal selection when he pushed the theory to the edges of
its necessary application. He then invented an auxiliary theory of suborganismal
selection to rescue himself from an uncomfortable corner; but he eventually
followed the relentless logic of his own argument to a full theory of hierarchy.
The theory of hierarchical selection does not constitute either a small and
merely incremental nuance, or a modern concoction and exaggeration of bored
Darwinians trying to stir up some trouble. Hierarchy has accompanied the theory
of selection from its very inception—if only because no truly tenacious and
thoughtful Darwinian could ever avoid its appeal and logic, while at least one of
the wisest and the most committed adherents, August Weismann, came to regard
hierarchy as the implied and necessary centerpiece of any evolutionary theory fully
rooted in selectionist principles, and truly comprehensive in explanatory range. We
have largely forgotten Weismann's intellectual journey today. But we should
recover his chain of argument—for his motives and insights retain full validity,
even if later discoveries about the physical basis of heredity invalidated his
particular form of suborganismal selection.
Darwin on the Principle of Divergence • Hints of Hierarchy in Supraorganismal Selection:
Darwin on Correlation of Parts
DIVERGENCE AND THE COMPLETION OF DARWIN'S SYSTEM
Charles Darwin cannot be judged as a consistently felicitous writer, but he could
turn a phrase with the very best of craftsmen. As noted before, many of his lines,
particularly his wonderful metaphors, have become parts of our culture—the image
of the "entangled bank" at the very end of the Origin, or the "tree of life" that
closes Chapter 4 on natural selection. His posthumously published autobiography
contains many memorable and oft-quoted statements, including his description of
intellectual eureka: "I can remember the very spot in the road, whilst in my
carriage, when to my joy the solution occurred to me" (in F. Darwin, 1887, vol. 1,
p. 84).
Poll our biological colleagues, and most will tell you that this horse-drawn
epiphany describes Darwin's Malthusian insight of September 1838, and the
resulting formulation of natural selection. But the passage refers to a much later
event, and this error of attribution may be the most common in all Darwinian
exegesis. The statement recounts an insight—the "principle of divergence" in his
own description—that Darwin ranked as equal in importance with natural selection
itself, an idea whose formulation sometime in the early to mid 1850's (the true date
of the carriage ride) allowed him to complete his theoretical structure and begin
writing his magnum opus.
Darwin describes the phenomenon that a principle of divergence must
resolve, and states his surprise at his own obtuseness before the fateful carriage
ride: