176 life
so. The manner in which data from biogeography, paleontology, embryology,
variation under domestication, and taxonomy were coordinated in a single
conceptual framework has often been seen as a perfect fulfillment of William
Whewell’s demand for consilience in a theory worth defending.^52 Darwin could
explain why there had been so much extinction, why (given divergence from
a common ancestor) the more ancient a fossil was the more intermediate a
form it had between existing species. He could explain why island species
resembled those of neighboring continents. He could incorporate the Malthu-
sian struggle for limited resources, which in September 1838 had given him
the key to his mechanism. He could even embrace fancy pigeons to show what
human selectors could do and thereby give substance to his metaphor of nat-
ural selection. If breeders could achieve such diversity from the common rock
pigeon, what might not nature have done with other species and with so much
more time on its hands?
A subtle unification was achieved at a metaphysical level. The birth and
death of species were presented as quintessentially no different in their expli-
cability from the birth and death of individuals. This was an important move
in rebutting naı ̈ve religious objections that supposed a Christian doctrine of
creation to require separate divine intervention for the origin of each and every
species. There is, however, one other aspect of Darwin’s unification that de-
serves special comment. This is his preference for locating the ultimate origin
of all species in a single life form. A predilection for unity might simply trans-
late into a thesis about a singularity of origin. In the closing lines of hisOrigin
of Species,Darwin had been careful to refer to one or afewprimordial forms
into which life had been breathed; but even he could not resist the lure of the
most economical solution. He was often tempted to take the further step, to
the belief that all animals and plants have descended from just one prototype.
This means that during the 1860s at least four explanations predicated on a
unity of origin were on the table for a world occupied by human beings.
At one extreme was the simple theism in which all was resolved into the
will of a single deity—an explanation that for Darwin explained nothing. At
the other extreme was the complete naturalism of a Darwinian such as John
Tyndall.^53 Competing intermediates were Darwin’s ambiguous position on
whether the first material form of life could be said to be the work of a Creator,
who created by laws; and the theism of Richard Owen, in which creation was
continuous as new instantiations of a divine archetype (a single archetype)
came into being.^54 In that competition, different models for the unity of nature
were in serious contention, and it almost goes without saying that deeply held
religious or metaphysical convictions helped to shape each of them.
And so to my concluding observation. Some commentators saw theological
advantages in a unified process of evolution in which, as Darwin had put it in
one of his early notebooks, we are all “netted together.” Darwin’s correspondent