$2 THE CAUSATION OF DISEASE. 



be strongly saturated with the same disease-tendency, it is 

 rare to find all the children inheriting it. There seems, 

 indeed, to be a great tendency in Nature to right herself in 

 the offspring, if she be allowed a fair chance — if the offspring, 

 namely, follow a hygienic mode of life.- We shall presently 

 see that this is due to the fact that diseases having for the 

 most part a recent ancestral origin tend, like all recently 

 acquired characters, to disappear in the offspring, not yet 

 having attained a sufficiently strong hold upon the race to 

 ensure their continued inheritance. But this tendency to 

 revert to a pre-pathologic state will of course be far greater 

 when only one parent is diseased (as in 2). Indeed, in such 

 cases it will often be very strong ; for, as already observed, 

 if one parent be especially vigorous in that particular wherein 

 the other fails, the two may be regarded as a cross in respect 

 of that particular, and hence there may be. a reversion to the 

 pre-pathologic state — namely, health. 



Some of the evil resulting from consanguineous marriages is 

 due to the blendings now under consideration — namely, of like 

 abnormalities of lika tissues, for the same morbid tendencies 

 are apt to exist in parents of near blood, as rheumatism, gout, 

 phthisis. In regard to consanguineous marriages Darwin 

 says :* " Whether consanguineous marriages, such as are 

 permitted in civilized nations, and which would not be con- 

 sidered as close inter-breeding in the case of our domesticated 

 animals, cause any injury, will never be known with certainty 

 until a census be taken with this object in view. My son, 

 George Darwin, has done what is possible at present by a 

 statistical investigation, and he has come to the conclusion, 

 from his own researches and those of Dr. Mitchell, that the 

 evidence as to any evil thus caused is conflicting, but, on 

 the whole, points to the evil being very small." But of 

 course the result will differ vastly according to the health -value 

 of the intermarrying family. If both parents, no matter how 

 closely related, be perfectly healthy, so also will be their 

 offspring. History tells us that consanguineous marriages 

 were once the custom among certain peoples, and that such 

 unions were attended with the happiest results as regards 



* " Variation under Domestication," vol. ii. p. 104. 



