The Theory of Evolution | 311 



tween Geospiza magnirosiris, G. fortis, and G. fuliginoso on In- 

 defatigable Island caused them to adapt to more specialized feeding 

 niches" sounds very impressive and scientific but is almost meaning- 

 less. The word "competition," for instance, has many meanings and 

 very unfortunate connotations. In this case, it might imply that at 

 first all three kinds of birds utilized the same limited food supply. 

 Competition is not between kinds but between individuals. If we 

 assume that there was at least a slight differentiation in food prefer- 

 ence in isolation, individuals of the same species would "compete" 

 with each other more strongly than with the individuals of other 

 species. Presumably, for food specialization to be enhanced, some 

 selective advantage would have to accrue to variants that tended to 

 restrict their diets to particular types of food. It is very difficult to 

 see the selective advantage of such restriction, but it must be tied in 

 with the presence of several different species because, where a spe- 

 cies occurs alone, its members tend to be more general feeders. The 

 problem may involve complex interactions among such factors as 

 feeding efficiency, recognition characteristics, psychological reactions 

 to individuals of other species, changes of the food supply in lean 

 years, the general structure of the ecosystem, and so forth. Whatever 

 the factors, more study is needed. 



There are many other points of disagreement among evolutionists, 

 some more important than others. Some biologists still think that 

 under certain circumstances populations of diploid outcrossing or- 

 ganisms may differentiate without the intervention of physical isola- 

 tion (through disruptive selection or positive assortative mating). 

 Others cite cogent reasons why this so-called sympatric speciation is 

 unlikely. As mentioned in Chap. 7, there is still considerable dis- 

 agreement on the role of drift in evolution, and the disagreement 

 will doubtless persist until more is known about natural populations. 



Much work needs to be done to clarify, and make operational (if 

 possible) concepts such as population fitness and adaptation. The 

 former concept is involved in such questions as Which is more fit, a 

 population showing a high degree of polymorphism or one that is 

 homozygous for superior alleles at most loci? This may be like ask- 

 ing: Which are better, apples or oranges? Certainly the question 

 cannot be answered until and unless a satisfactory definition of 

 population fitness can be formulated. 



Adaptation is one of the most overused terms in biology. Natural 

 selection has become recognized as an a posteriori description of 

 events, but adaptation, the result of selection, has been relatively 

 tenacious of its status as a thing. It is difficult to see much merit in 

 the term, as all known organisms are the result of more than a billion 



