MEANS AND METHODS OF EVOLUTIONARY CHANGE 341 



are passed on to offspring, who therefore are different from what they other- 

 wise would have been. We see readily that this theory, if correct, provides 

 a simple and direct means for the production of diversity. 



An example may help to make the application clear. We have seen that 

 the ancestors of the modern horse left the woods and took to life on the dry 

 plains of the West (pp. 201-206). The change was accompanied by change 

 in length and structure of the legs, making possible increased speed in run- 

 ning over hard ground. In line with Lamarck's theory we may postulate that 

 the first ancestral horses to venture forth on the plains were chased by 

 predatory animals, packs of wolves, perhaps. In running to evade these 

 predators they would have increased the power of their legs (as our college 

 sprinter increases the power of his by practice). Any gains in muscular 

 strength and efficiency, and in length, of leg acquired in this manner would, 

 according to the theory, be passed on to the offspring of the animals which 

 acquired them. Thus the offspring would begin life with better legs for 

 running than their parents had had when they began life. 



But still the chase by predators would continue. By continued use of their 

 legs for running away, the horses of this second generation would add 

 another increment of strength and length, which would be passed on to the 

 third generation. And so on, generation after generation, each generation 

 improving on its heritage slightly and passing its gains on to its offspring. 

 An analogy would be increase in a family fortune passed on from father to 

 son in pre-inheritance-tax days, each generation adding to what had been 

 received from its immediate predecessor. So after many generations the 

 elongated and efficiently muscled legs of the modern horse evolved, // the 

 Lamarckian explanation is correct. 



The Lamarckian theory appeals because of its directness and relative 

 simplicity. Biologists confronted with manifold instances of animals, past 

 and present, adapted to their particular needs and environments with exqui- 

 site nicety find in the theory a satisfying means of visualizing how perfect 

 adjustment between animal and environment can be achieved. What more 

 natural than to suppose that whales developed the perfection of their 

 streamlining through the action, for millions of years, of water pressure 

 against their bodies as they swam? May it not be that the water molded 

 the body gradually, the changes in shape, once acquired, becoming heredi- 

 tary? Such a direct process of evolution is easy to visualize and has a forth- 

 rightness about it which to many biologists seems lacking in the means and 

 methods of evolution to be described presently. But should we expect nature 

 to be simple and forthright? 



We return to the central question: Are characteristics developed by an 



