230 THE STRUCTURE OF EVOLUTIONARY THEORY
of the same order; the surface of the island would no doubt be pretty well
clothed with plants and there would be many individuals of these species
and of the few well adapted insects; but assuredly there would be seasons
of the year, peculiar and intermediate stations and depths of the soil,
decaying organic matter etc., which would not be well searched for food,
and the amount of life would be consequently less, than if our island had
been stocked with hundreds of forms, belonging to the most diversified
orders (ibid., p. 228).Darwin then provides examples from agriculture and domestication. Several
varieties of wheat, sown together on a plot, will yield more grain per acre than a
monoculture. In one experiment, two species of grass yielded 470 plants per square
foot, while a plot of 8 to 20 species produced a thousand plants per square foot
(ibid., p. 229): "I presume that it will not be disputed that on a large farm, a greater
weight of flesh, bones, and blood could be raised within a given time by keeping
cattle, sheep, goats, horses, asses, pigs, rabbits and poultry, than if only cattle had
been kept" (ibid., p. 229).
But why was Darwin so wedded to a principle of maximization that would
strike most of us today as both metaphysical and indefensible (ecosystems, after
all, can work perfectly well with far fewer species and lower chemical "yield" per
spot)? Schweber (1980), I think, has provided the correct answer by stressing
Darwin's allegiance to one of the most popular philosophical approaches of his
day—the "Benthamite optimization calculus" promoted by Jeremy Bentham, and
many other prominent thinkers in several disciplines, as the utilitarian principle in
philosophy and political economy, the "greatest good for the greatest number."
William Paley, the intellectual hero of Darwin's youth (see p. 116), spoke for a
utilitarian consensus in writing (quoted in Schweber, 1980, p. 263): "The final
view of all rational politics is, to promote the greatest quantity of happiness in a
given tract of country ... and the quantity of happiness can only be augmented by
increasing the number of percipients or the pleasure of their perceptions." In other
words, make more objects and make them better. Nature achieves this desired
maximization and progress by diversifying the number of species in each region of
the globe.
Darwin explicates and defends the maximization of life with his favorite
rhetorical device—analogy—and by invoking another fundamental tenet in the
political economy of his era: the division of labor. As taxa specialize ever more
precisely to definite and restricted roles in local ecologies, more species can be
supported (leading to maximization of life as measured by chemical throughput).
In a note of September 23, 1856, Darwin drew a direct parallel between
diversification in nature and the economic principle of division of labor: "The
advantage in each group becoming as different as possible, may be compared to
the fact that by division of labor most people can be supported in each country."
For the public presentation in the Origin three years later, Darwin retained the
centrality of division of labor, but chose a biological analogy drawn from the
French zoologist Henri Milne Edwards (who had, himself, credited Adam Smith
and the political economists, and who characterized his own view as an extension