Fitness in the Living World 3 * 5 



The more common relationships of individuals of the 

 same species, as for example between males and females, 

 parents and offspring, and all the castes with their different 

 functions among social insects, are notable instances of adap- 

 tation. What is more wonderful than the great drama of 

 sex, in which all living things, except the very lowest plants 

 (bacteria), are actors, in which admirable coadaptations 

 for bringing about cross fertilization are found, all the way 

 from the structures and functions of the egg and sperma- 

 tozoon to the secondary sexual characters and the compli- 

 cated instincts and behavior of males and females? Consider 

 the very common adaptations found in the relations of 

 parents and offspring, the various methods by which the 

 young are protected and supplied with food, and the com- 

 plicated behavior which characterizes this relationship in 

 higher animals. 



4. Adaptations of Development 



To the embryologist at least, no adaptations are more 

 striking than those of development. In the normal develop- 

 ment of an egg or embryo every step leads to what seems 

 to be a preconceived end. The differentiations of ontogeny 

 are usually adaptive. The cleavage of the egg subdivides the 

 egg substance both quantitatively and qualitatively in such 

 manner as to determine the relative sizes and locations of 

 future parts. Even the distribution of substances in the un- 

 segmented egg may foreshadow the proportions and locali- 

 zations of future organs. These organs develop not for 

 immediate but for future uses and in anticipation of distant 

 needs. For example, consider the development of the eye; 

 the retina with its sensory rods and cones, the lens with the 

 ciliary processes and muscles for focusing, the transparent 

 cornea and humor each and every portion of the organ 



