534 THE POPULAR SCIENCE MONTHLY 



lative, but Beeton and Pearson^* have succeeded in obtaining more defi- 

 nite evidence. 



From extensive researches on inheritance in man, Pearson and his 

 associates have shown that duration of life gives much lower correla- 

 tions — both parental and fraternal — ^than the substantial values found 

 for other physical and psychical characters. If the duration of life of 

 an individual were absolutely determined by physical and mental fit- 

 ness, then one would expect it to show a correlation as high as that 

 found for other characters. The fact that the values are regularly and 

 conspicuously lower evidences for the existence of a non-selective death 

 rate. The relative amount of the selective and non-selective death rate 

 may be roughly estimated from the reduction in correlation as one passes 

 from the inheritance of characters in general to that of longevity. 

 By this means Beeton and Pearson calculated that from fifty to eighty 

 per cent, of the death rate in civilized man is selective. 



C. The Fitness of Organs 



Except among the lowest forms of life, every animal or plant is 

 made up of a large number of parts which are differentiated in form 

 and function. The fitness of such a complex organism for self preser- 

 vation and perpetuation probably depends not merely upon the degree 

 of development of its several component members, but also upon the 

 nicety with which they are coordinated. 



Undoubtedly the proper way of taking up the study of Natural 

 Selection is to compare by means of the measurement of particular 

 organs series of individuals which survive with series which perish, 

 but after this is done in a large number of cases we shall have con- 

 sidered only the first part of our problem. 



This first phase consists in finding out whether variations in the 

 form, size or other property of an organ affects its efficiency to such an 

 extent as to prejudice the chances of survival of the individual possess- 

 ing it" 



Involving, as it does, questions of structural characteristics and 

 functional efficiency this is at bottom a problem on the boundary line 

 between morphology and physiology. For several years it has seemed 

 tc me that we might, in the long run, make better progress in the study 

 of the problems of evolution if we turned our backs on some of its more 



" Beeton, Mary, and K. Pearson, ' ' A First Study of the Inheritance of 

 Longevity and the Selective Death-rate in Man," Proc. Eoy. Soc. Lond., Vol. 

 LXV., pp. 290-305, 1889. Beeton, Mary, and K. Pearson, "On the Inheritance 

 of the Duration of Life, and on the Intensity of Natural Selection in Man," 

 BiomeiHka, Vol. I., pp. 50-89, 1901. 



*In actual work one is at once confronted by the difficulty that variations 

 in the organ he is studying may have no real influence upon the chances of sur- 

 vival but merely an apparent significance due to its correlation with other organs. 



