CHAPTER XI 



SOME TEST CASES BETWEEN THE 

 RIVAL THEORIES 



B. MORPHOLOGICAL 



iN AT URAL selection, being a conmion phenomenon of everyday 

 experience, has exercised such a fascination that it has to a 

 notable extent inhibited people from trying properly to think 

 out how a principle, whose essence is competition with partial 

 escapes into usually temporary success every now and then by 

 improved adaptation, can produce the ordered arrangement, 

 taxonomy, and morphological or structural uniformity with which 

 we are familiar. Herschel the astronomer, in an early criticism of 

 the Origin of Species, is said to have called it the "law of 

 higgledy-piggledy", and when one tries to imagine what mor- 

 phology would be, under its unrestricted operation, it is difficult 

 to meet this criticism. Why should natural selection produce such 

 comparative uniformity in morphological structure? Why should 

 there be such morphological likeness between the members of 

 whole families, tribes, genera, or even divisions like the Mono- 

 cotyledons? Why should the morphology remain the same, and 

 not improve in later evolutions? Why should the larger (older) 

 families appear in almost every kind of ecological conditions, 

 though the members of any one of these families show greater 

 structural resemblance among themselves than do the plants of 

 the association that inhabits any given spot? A grass is an un- 

 mistakable grass, whether in the tropics or in the arctic zone, in 

 a dry or in a wet climate, in a bog or on a moor. To say that this 

 is the case because it is a grass, and must retain the morphology 

 of a grass, is no explanation, but only throws the task of explana- 

 tion a little further back. Why and how were the grasses, or the 

 crucifers, or the composites, evolved at all? Why is there nothing 

 in common, in structural features, between say a grass and a 

 crucifer growing in the same kind of conditions, and side by side, 

 on a moor or in a pasture? One would expect natural selection, 

 working by gradual adaptation to similar conditions, and deter- 

 mining the structural features (as it must do if it is to be an 

 explanation of evolution) to produce something of similarity. In 



