CAUSES OF EVOLUTION 247 



birds, and mammals that we may interpret the similarities of 

 form evolution and understand why, the other three causes 

 being similar, mammals repeat so many of the habitat form 

 phases in adaptation to the environments previously passed 

 through by the lower orders of life. Thus advancing struc- 

 tural complexity is the reflection or the mirror of the invisible 

 physicochemical complexity; the visible structural complexity 

 of a great animal like the whale (Fig. 234), for example, is 

 something we can grasp through its anatomy; the physico- 

 chemical complexity of the whale is quite inconceivable. 



In research relating to the physicochemical complexity of 

 the mammals, so notably stimulated by the work of Ehrlich 

 and further advanced by later investigators, there are perhaps 

 few studies more illuminating than those of Reichert and 

 Brown^ on the crystals of oxyhemoglobin, the red coloring 

 matter of the mammalian blood. Their research proves that 

 every species of mammal has its highly distinctive specific 

 and generic form of hemoglobin crystals, that various degrees 

 of kinship and specific affinity are indicated in the crystallog- 

 raphy of the hemoglobin. For example, varieties of the dog 

 family, such as the domestic dog, the wolf, the Australian 

 dingo, the red, Arctic, and gray fox, are all distinguished by 

 only slightly differing crystalline forms of oxyhemoglobin. The 

 authors' philosophic conclusions arising from this research are 

 as follows:^ 



"The possibilities of an inconceivable number of constitu- 

 tional differences in any given protein are instanced in the fact 

 that the serum-albumin molecule may, as has been estimated, 

 have as many as 1,000,000,000 stereoisomers. If we assume 

 that serum-globulin, myoalbumin, and other of the highest pro- 



1 Reichert, E. T., and Brown, A. P., 1909, pp. iii-iv. 



' Certain insertions in brackets being made for purposes of comparison with other 

 portions of this series of lectures. 



