Seeds of Hierarchy 211
Obviously, Roux had adopted Darwinian language for his title. Just as
obviously, he hoped to apply the Darwinian apparatus at a level below its
conventional locus of organisms. Roux's book surely occupies a place in the
history of hierarchy theory, if only because its verbal image of struggling parts led
many evolutionists, notably Weismann himself, to consider multiple levels of
selection. But, curiously, as several critics soon noted (Plate, 1905; Kellogg, 1907;
and even, with some ambiguity, Weismann, 1904, as well), Roux's theory does not
really treat descent at all. Weismann's germinal selection, as we shall see, is a true
theory of suborganismal selection and inheritance; but Roux's battle of the parts
includes no statement about heredity, and ranks instead as a theory of functional
adjustment in development.
Roux argued that the construction of a harmonious and well-designed
organism emerges from a struggle among parts competing for limited nutriment.
Lung cells compete with liver cells, and bone cells battle with other bone cells for
best locations in the flow of nutriment. To cite Roux's favorite example, made even
more famous by D'Arcy Thompson's later analysis (1917, and see Chapter 11, pp.
1195 - 1196), the bony trabeculae in the head of a human femur form a virtual
diagram of forces imposed on the bone during locomotion, and must therefore be
optimally designed to counter stress. But no one can argue that details of the
arrangement in any single bone represent an evolutionary adaptation, if only
because the trabeculae of a broken, and improperly mended, femur reform along
the new stress lines of a limping walk.
Roux argued that stresses establish lines of preferred flow for nutriment. Bone
cells that happen to lie in the stream prosper and proliferate; others in less
advantageous positions wither and die—leading to a functional honeycomb of
struts and empty spaces. Roux used this argument to explain the functional design
of tissues and organs in general, but he focused upon such complex and exquisite
examples of optimal form as the barbules on bird feathers, the hairs that cover the
spiracles of many insects, the arrangement of muscle fibers in the walls of blood
vessels, and the bony trabeculae discussed above.
This "battle of the parts" may account for the flexible construction of optimal
form in each organism. Indeed, such a principle, appropriately modernized,
remains essential for a developmental biology that cannot invoke a specially
tailored gene for each villus on an intestinal surface. But Roux's proposal cannot
operate as a theory of evolutionary change for two reasons. First, the struggling
parts do not vary in heritable ways, and victory cannot lead to beneficial changes in
future generations. Bone cells that prosper on the growing trabeculae cannot be
designated as superior to, or even in any sense intrinsically different from, the
losing cells that die for lack of nutriment in the spaces between. The winners owe
their success only to the good fortune of a favorable location. Kellogg (1907, p.
207) wrote: "This competition depends chiefly on the hazard of position ... Not the
best qualified but the best situated fibers have vanquished the others by robbing
them of food and thus finally destroying them." Second, Roux's Kampf der Theile
includes no theory