Fisher's Axiom and the Body Size of Animals

What is here called Fisher's axiom states that all large mutations are deleterious, and the consequence of this is the generally accepted Darwinian notion that all evolutionary progress must have occurred through the accumulation of small mutational steps. We have in the present paper tested the postulate that one parameter, namely, the body size (weight or volume) does not vary in this way, but rather in steps which are powers of two, up to or down, as the case may be. The outcome of our analysis is that this hypothesis is corroborated with fair significance for certain, randomly selected, groups of living and extinct animals. The consequences of this observation are briefly discussed.