204 THE STRUCTURE OF EVOLUTIONARY THEORY
writing more than 300 popular monthly essays on evolutionary topics during the
past 25 years, I have become a statistically adequate sampling point, through
thousands of letters received from lay readers, for both the frequency and intensity
of standard confusions about our profession. I can testify that three items top the
list of puzzlement: (1) evolution seen as anagenesis rather than branching ("if
humans evolved from apes, why are apes still around"); (2) panselectionism ("what
is the adaptive significance of male nipples"); and (3) Lamarckism and the failure
of natural selection ("doesn't the blindness of cave fishes imply a necessary space
for Lamarckian evolution by disuse").)
The problem of incipiency in degeneration poses more difficulty than the
opposite issue of construction—for what can mediate the sequence if selection
does not regulate the final outcome? Weismann struggled to encompass this issue
with his favored apparatus of Allmacht for selection—and he failed. Degeneration
acted as the lever that pried Weismann from his panselectionism, and led him
through a chronological series of honorable changes that must be read, in one
sense, as retreats from a former pugnacious insistence on Allmacht, but that also
represents a complexification and strengthening of his original views.
Consider the example that Spencer raised with such effectiveness against
Weismann, and that eventually prompted the theory of germinal selection—
reduction of hind limbs in some whales to tiny vestiges with no exterior expression
at all. Two classical explanations had been invoked by panselectionists: (1) the
limbs became so reduced by ordinary negative selection, as a consequence of the
hindrances they imposed upon efficient, streamlined swimming; (2) the limbs are
not, in themselves, harmful, but energy invested in any useless structure must
handicap a creature relative to conspecifics with fewer vestiges and neutral organs.
Weismann invoked these standard arguments, but he became convinced (long
before his debate with Spencer) that only part of the puzzle could be resolved
thereby. Selection would reduce the limbs to some degree (perhaps considerably),
but surely the increments of further reduction soon become too small for granting a
continuing, believable role to selection. Consider the figures that Spencer presents
(1893b, p. 25), based on the efforts of a Dr. Struthers of Aberdeen, who had
"kindly taken much trouble in furnishing the needful data, based upon direct
weighing and measuring and estimation of specific gravity." Spencer cites a
Greenland Right Whale, weight 44,800 pounds, femur weight, 3-1/2 ounces; and a
Razorback at 56,000 pounds, with a femur weight of 1 ounce—"so that these
vanishing remnants of hind limbs weighed but 1/896,000th part of the animal."
Could one possibly believe that a profound relative, but inconsequential absolute,
reduction—from a two-ounce to a one-ounce femur, for example—might
materially aid streamlining (especially since external expression had disappeared
long before) or conserve meaningful energy? Weismann accepted the
implausibility of such a claim and recognized that he would have to seek an
explanation beyond