my case on fulfilled expectations drawn from ecological and evolu- tionary theory. To these, I now turn.

A Critique of the Classical Significance
of Heterochrony

The Classical Arguments

Traditional views die hard, and their influence extends long past the time of their public abandonment. In its heyday, recapitulation was the motor of evolutionary progress, a mechanism to build increasing complexity by adding new stages to previous, simpler ontogenies. Paedomorphosis, in this light, is degenerative; it merely lops stages off a complex ontogeny and returns an organism to a simpler, ancestral state (literally, in fact, to the adult stage of a long-extinct forebear).

Few modern authors would state the traditional view as baldly as Ruzhentsev has: "Ontogenetic recapitulation is one of the basic laws of movement in the organic world, a replacement of one form of life by another, more perfect one" (1963, p. 943). Yet the influence of recapitulation lingers, if only in setting the stage for criticism.

It has lingered more directly in the persistent statement that one mode of paedomorphosis is degenerate and nonprogressive— progenesis, or juvenilization by the acceleration of maturation and the truncation of ontogeny. Simplification of form, shortening of the life span, and reversion to a largely unaltered larval or juvenile morphology have been contrasted unfavorably with the prolongation and potential for complexity associated with evolutionary progress. To Cloud (1948, p. 333), progenesis is "strictly regressive"; to de Beer (1958, p. 64) it is "of no significance in progressive evolution." Wake writes: "Paedogenesis [= progenesis] is genetically fixed, leads to specialization and degeneration, and is of little significance as far as future phylogenetic progress is concerned" (1966, p. 79).

Neoteny, on the other hand, has been granted a progressive role, for here ontogeny is maintained at its ancestral length (or even extended) while specific somatic features are delayed in appearance. De Beer writes: "If [paedomorphosis] is achieved by accelerating the rate of development of the reproductive glands and hastening the time of maturity, the phylogeny usually results in a simplification often associated with parasitism. But if [it] is brought about by a slowing down of the rate of development of the body relatively to that of the reproductive glands, then changes are brought about which have considerable importance in phylogeny" (1930, pp. 70–71).