332 THE INDUCTIONS OF BIOLOGY. 



casts off cannot habitually contain tlie same proportions ; and 

 we may expect the proportions to vary not slightly but 

 greatly. Just as, during tlie evolution of an organism, the 

 physiological units derived from the two parents tend to 

 segregate, and produce likeness to the male parent in this 

 part and to the female parent in that; so, during the forma- 

 tion of reproductive cells, there will arise in one a predomi- 

 nance of the physiological units derived from the father, and 

 in another a predominance of the physiological units derived 

 from the mother. Thus, then, every fertilized germ, be- 

 sides containing different amounts of the two parental influ- 

 ences, will contain different Tcinds of influences — ^this having 

 received a marked impress from one grandparent, and that 

 from another. Without further exposition the reader will 

 see how this cause of complication, running back through 

 each line of ancestry, must produce in every germ numerous 

 minute differences among the units. 



Here, then, we have a clue to the multiplied variations, 

 and sometimes extreme variations, that arise in races which 

 have once begun to vary. Amid countless different combina- 

 tions of units derived from parents, and through them from 

 ancestors, immediate and remote — amid the various conflicts 

 in their slightly-different organic polarities, opposing and 

 conspiring with one another in all ways and degrees; there 

 will from time to time arise special proportions causing 

 special deviations. From the general law of probabilities it 

 may be concluded that while these involved influences, derived 

 from many progenitors, must, on the average of cases, ob- 

 scure and partially neutralize one another; there must occa- 

 sionally result such combinations of them as will produce 

 considerable divergences from average structures; and, at 

 rare intervals, such combinations as will produce very marked 

 divergences. There is thus a correspondence between the 

 inferable results and the results as habitually witnessed. 



§ 90. Still there remains a difficulty. It may be said that 



