370 THE STRUCTURE OF EVOLUTIONARY THEORY
needs impel adaptive change. (Cope's subsequent shift to a functionalist position
prompted the development of his later Neo-Lamarckism.) Cope wrote in 1870
(quoted in Cope, 1887, pp. 145-146): "We look upon progress as the result of the
expenditure of some force forearranged for that end. It may become, then, a
question whether in characters of high grade the habit or use is not rather the result
of the acquisition of the structure than the structure the result of the encouragement
it offered to its assumed beginnings by its use."
Hyatt differed from Cope in an essential manner that made his theory the
most uncompromisingly recapitulatory of all 19th century views, the most
committed of all proposed evolutionary mechanics to "programmed" racial life
cycles, and the most orthogenetic. Cope had provided the obvious interpretation for
a standard 19th century perception that, whereas most lineages progressed by
complexification, others regressed to greater simplicity. Cope argued that
progressive lineages undergo acceleration and therefore "gain room" to add new
stages to the end of old ontogenies; regressive lineages, on the other hand,
experience ontogenetic retardation and never surpass the juvenile stages of their
ancestry. Hyatt, in a paradox resolved by an ingenious argument, tried to render
both progressive and regressive evolution as results of acceleration alone. For
Hyatt, the law of acceleration reigned virtually without exception; no more
extensive or uncompromising version of universal recapitulation has ever been
offered.
Hyatt resolved the apparent paradox with an argument that he affectionately
called his "old age theory." The programmed steps of a potential phylogeny
proceed through a sequence more than merely analogous to the phases of
ontogeny. Adult stages of early species in a lineage exhibit traits of phyletic youth;
adults in a lineage's geological midlife display the features of phyletic maturity;
while adults of species near the extinction of a lineage finally develop
unmistakable signs of phyletic senility. Hyatt's hardest-line, internally programmed
version of orthogenesis rests upon this notion of a phyletic life cycle. The stages of
a phylogeny become as predictable and predetermined as the phases of an
ontogenetic sequence. Environment must be sufficiently favorable to permit the
unfolding (just as a fetus will not grow without adequate nutrition), but the
sequence of stages is internally ordained, not functionally entrained by interaction
with a surrounding environment. Hyatt wrote (1897, pp. 91-92): "There is a rise of
the individual through progressive stages of development to the adult and a decline
through old age to extinction. In the evolution of the stock to which the individual
belongs there is a similar law, a rise through progressive stages of evolution to an
acme and a decline through retrogressive stages to extinction... The type, like the
individual, has only a limited store of vitality, and both must progress and
retrogress, complete a cycle and finally die out, in obedience to the same law."
In this scheme, even the simplified ontogenies of regressive evolution can
arise by acceleration (see Fig. 5-3). The adult stages of phyletic old age resemble,
by analogy to the "second childhood" of our own senility, the simple features of
youth (although these recurring traits signify decline and extinction, rather than
exuberance, as they now appear in an exhausted stock). By this