ADAPTATION 



637 



explain ontogeny at all." The pattern of 

 the genes is subject to selective sorting in 

 terms of function during development and 

 in the adult. Phylogeny is a history of these 

 changes. Ontogeny depends largely on 

 these gene systems. Can we not assume, 

 then, that phylogeny has affected ontogeny 

 and that ontogeny has affected phylogeny? 

 These two aspects of life are manifestations 

 of basic protoplasmic capacities, and these 

 are guided during evolution by the envi- 

 ronmental elimination of the unfit. Perspec- 

 tive concerning fundamental relationships 

 resolves many controversies based upon 

 narrow viewpoints, and both sides of the 

 argument may often be brought into agree- 

 ment (Holmes, 1944a). 



We conclude that caenogenesis and 

 palingenesis, together with their related 

 principles of deuterogenesis, neoteny, foe- 

 talization (paedomorphosis), and recapit- 

 ulation, are examples of ancient and recent 

 adaptations in various stages of individual 

 and population Hfe cycles. These onto- 

 genetic adaptations manifest themselves in 

 behavior as well as morphology, and both 

 are the result of physiology initiated by 

 genetic systems. The temporal individual 

 (including the individual Hfe history stages 

 and metamorphosis) and the temporal 

 population are subject to selection as units. 



ALLOMETRY AND ORTHOGENESIS 



It has been noted, particularly by pale- 

 ontologists, that some organisms seem to 

 evolve beyond adaptive efficiency toward 

 extinction. The bivalve mollusks of the 

 genus Grijphaea developed extreme coiling 

 of the shell that must have made a wide 

 opening impossible, and opening at all 

 difficult in old individuals (Haldane, 1932; 

 Simpson, 1944, p. 174). The races that 

 evolved in this direction soon became ex- 

 tinct, but it is not clear that this momen- 

 tum in an unadaptive direction resulted in 

 extinction. 



Large deer have proportionately larger 

 antlers than small deer, and this relation- 

 ship pertains to both ontogeny and phy- 

 logeny. Such an allometric relationship be- 

 tween body size and antler growth places 

 a limit on the size of the animal, a limit 

 that seems to have been approximated by 

 the extinct Irish stag. 



As the limit of such a relationship be- 

 tween two characters is approached, selec- 



tion pressure may be increased, and a 

 slight change in the environment might 

 ehminate the species that have an un- 

 balanced condition (Simpson, 1944, p. 

 177). 



The allometric formula Y — hX'' has 

 been found to apply to a large number of 

 ontogenetic and phylogenetic series. Y and 

 X are the measurements of the compared 

 characters; h and k are constants. This 

 equation can also be written log Y = log h + 

 k log X, meaning that any magnitude con- 

 forming to tliis formula will fall along a 

 straight hue if plotted on a double loga- 

 rithmic grid (Huxley, 1932, p. 4). The 

 value k gives the angle of the slope of the 

 straight line. The value h gives the eleva- 

 tion of the straight line. 



Robb (1935) showed that the absolute 

 rate of increase of the preoptic region of 

 the horse skull is different from the abso- 

 lute rate of increase of the total skull 

 length, but that the two measurements 

 maintain a constant ratio to each other that 

 can be expressed in the equation Y = 

 0.25X^ ", in which Y is the preoptic 

 length, X is the skull length, 0.25 is the 

 fractional coefficient or the fraction of X 

 that Y occupies when X equals unity, and 

 1.23 is the ratio of the rate of increase in ^ 

 to that in X. As pointed out by Simpson 

 (1944), such an equation applies to the 

 phylogenetic sequence, to existing races or 

 species of horses of different size, to the 

 ontogenetic development of the individual, 

 and, in horses, probably to adults of dif- 

 ferent sizes in a single race. Ontogeny 

 seems to repeat phylogeny in such a case, 

 but there is no indication that this type of 

 recapitulation is the result of any genetic 

 or functional change. 



Robb (1936, 1937) expressed the rela- 

 tions of the side toes (digits II and 

 IV = Y) to the middle toe (metapodial of 

 digit III = X) in the three-toed horses by 

 the equation Y = 1.4 to 1.5Xo »" '° "•»». 

 However, in the ontogeny and phylogeny 

 of the single-toed horses the equation is 

 Y = 0.75 to 0.76X0^^ •" ^ "". There is thus 

 a fairly abrupt change in h associated with 

 a change in function of the side toes. This 

 may be construed as a possible influence 

 of selection upon the proportional relations 

 of such characters. The side toes in the 

 modern horse would probably be an en- 

 cumbrance, as well as useless (p. 673). 



