The Wheel
of Fortune and the Wedge of ProgressBE PREPARED: A great motto for
Boy Scouts, but not too relevant for life's cosmic game of craps by
Stephen Jay Gould Charles Darwin was a master of metaphor, and much
of his success may be attributed to his uncanny feel for timely comparisons that
virtually compel understanding. We all know the two metaphors that Darwin invoked
to define his theory: natural selection and the struggle for existence. We might
also consider Darwin's three principal descriptions of nature, each wonderfully
apt and poetic, and each a metaphor.
The
tangled bank. To stress the intricacy of relationships among organisms
as arising, somewhat paradoxically, by plan-less evolution. Darwin begins
the last paragraph of the Origin of Species:
It is interesting to contemplate an entangled bank, clothed with many
plants of many kinds, with birds singing on the bushes, with various insects
flitting about, and with worms crawling through the damp earth, and to
reflect that these elaborately constructed forms, so different from each
other, and dependent on each other in complex a manner, have all been
produced by laws acting around us.
The
tree of life: Borrowed from other contexts to be sure (Proverbs 3:18,
for example), but used brilliantly by Darwin to express the other form
of inter-connectedness--genealogical rather than ecological--and
to illustrate both success and failure in the history of life. Darwin
placed this famous passage at a crucial spot in his text--the very
end of chapter four, which marked the conclusion of his argument for natural
selection (the rest of the book discusses problems and examples):
As buds
give rise by growth to fresh buds, and these, if vigorous, branch out and overtop
on all sides many a feebler branch, so by generation I believe it has been with
the great Tree of Life, which fills with its dead and broken branches the crust
of the earth, and covers the surface with its ever branching and beautiful ramifications. The
face of nature (and the darkness behind): To argue that apparent balance and
harmony arise from the struggle and death of individuals:
We behold the face of nature bright with gladness, we often see superabundance
of food; we do not see, or we forget, that the birds which are idly singing
round us mostly live on insects or seeds, and are thus constantly destroying
life; or we forget how largely these songsters, or their eggs, or their
nestlings, are destroyed by birds and beasts of prey.
But if Darwin relied on metaphors to enlighten his
readers, he also followed this good strategy in his private quest for understanding.
Darwin's notebooks are, if anything, more awash in metaphor than his published
works. I believe, along with many Darwin scholars (see, in particular, Ralph Colp's
"Charles Darwin's Vision of Organic Nature," in the New York State
Journal of Medicine, September 1979), that one metaphor stands out among all
others in Darwin's own struggle to formulate the principles of natural selection--the
metaphor of the wedge. At the very least, this comparison holds pride of place
as the first image invoked by Darwin to explicate his initial statement of natural
selection.Great ideas, like species, do not have "eureka"
moments of sudden formulation in all their subtle complexity; rather, they ooze
into existence along tortuous paths lined with blind alleys (to invoke a metaphor).
Still, not all moments are equal, and some may even be judged crucial. Darwin,
at least, claimed that September 28, 1838, had been the key day for natural selection,
and that his reading of Thomas Malthus's Essay on the Principles of Population
had enabled him to put the disparate pieces of his puzzle together, as he grasped
Malthus's argument that growth in population, if unchecked, must quickly outstrip
food supply, leading to inevitable struggle for limited resources and death for
losers. He wrote Malthus's principle into his notebook and appended, directly
thereafter, his very first metaphor for his new theory of evolution:One
may say there is a force like a hundred thousand wedges trying [to] force every
kind of adapted structure into the gaps in the economy of nature, or rather forming
gaps by thrusting out weaker ones. Darwin honed and sharpened this image
throughout the next twenty years, as he prepared for the storm of publishing his
ideas about evolution. He eventually settled upon the image of a surface absolutely
chock-full with wedges, representing species in an economy of nature sporting
a No Vacancy sign. Evolutionary change can only occur when one species manages
to insinuate itself into this fullness by driving (wedging) another species out.
Darwin developed this metaphor most fully in his manuscript for the long, unpublished
version of the Origin of Species (a compressed account appears on page
67 of the shorter book that he eventually produced in 1859 under the pressure
of A. R. Wallace's independent formulation of natural selection):
Nature may be compared to a surface covered with ten thousand sharp wedges,
many of the same shape and many of different shapes representing different
species, all packed closely together and all driven in by incessant blows:
the blows being far severer at one time than at another, sometimes a wedge
of one form and sometimes another being struck, the one driven deeply
in forc-
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