Please see Impact No. 95.

For your convenience, Parts I (Impact No. 95) and II (Impact No. 96) have been included together in Impact No. 95.

Horses only 15 inches high, 141 tree species in a single acre of tropical rain forest—what spectacular variety we see among living things, both variation within kind and the stupendous number of different kinds.

An intriguing development in recent evolutionary thought has been the growing repudiation of neo-Darwinian orthodoxy (that is, the idea of slow and gradual evolution, accomplished by the mechanism of small random genetic mutations preserved by natural selection) in favor of the idea of rapid evolution caused by rapid environmental changes.