Why Does Recapitulation Dominate
the History of Life?

For one committed, as Cope was, to the preeminent importance of recapitulation in evolution, this system leaves one point unanswered: If the law governing recapitulation is that of acceleration and retardation, why does recapitulation dominate? The law provides equally for recapitulation by acceleration and for its opposite, paedomorphosis by retardation. Moreover, it offers no reason for believing that cases of recapitulation should exceed those of paedomorphosis.

On one level, this dilemma has a simple resolution. We grant more emphasis to recapitulation because it is the necessary result of progressive evolution, and progressive evolution is more interesting and important, if only because it led to us. But this is not enough. Cope believed that cases of recapitulation far exceeded those of paedomorphosis in frequency as well as in importance. There must be some force impelling the general speed of development to accelerate through geologic time. In later works, Cope seems to favor an internal explanation, a type of energy that inheres in organic matter and accelerates its speed of development through time. In 1896 (p. 448), he speaks of "the phenomena of the building or growth of the added characters which constitute progressive evolution as evidence of the existence of a peculiar species of energy, which I termed bathmism."

In an earlier work (1870), however, he proposed an external explanation of great ingenuity. Acceleration may predominate because a directional change in atmospheric composition entails the speeding up of developmental rates. Development is tied to metabolism, metabolism to respiration and oxygen. The great coal deposits of Carboniferous times reflect the removal of vast amounts of carbon dioxide from the earth's atmosphere. This removal probably implies a rise in the level of oxygen. If oxygen has increased with time, so has respiration, metabolism, speed of development, and frequency of acceleration over retardation. Cope then cites the great thickness of fossil coals and mentions that the most luxurious vegetation today takes 50 tons of carbon from the atmosphere per century per acre, but produces from this a layer of coal only l/3 inch thick:

The atmosphere, thus deprived of a large proportion of carbonic acid, would in subsequent periods undoubtedly possess an improved capacity for the support of animal life. The successively higher degree of oxidation of the blood in the organs designed for that function, whether performing it in water or air, would certainly accelerate the performance of all the vital functions, and among others that of growth. Thus it may be that acceleration can be ac-