Ix THE ANIMAL KINGDOM. 



turns gray in early life ; immunity from small-pox in some families is said to be a well- 

 established fact ; muscular strength, as seen in running, wrestling, and boating, as well 

 as dancing, singing, lisping, loquacity and its opposite, and peculiarities in penmanship 

 and even certain habits besides various physical defects are more or less hereditary ; 

 and artificial deformities, such as flat heads in the North American Indians, while the 

 peculiar methods practised by certain Peruvian tribes, the Aymaras, the Huancas, and 

 the Chinchas, respectively, are known to have been transmitted. Yet there are many 

 exceptions to the law of heredity, especially as regards temporary and accidental modifi- 

 cations, such as circumcision, etc. As a rule, however, not only physical but mental 

 characteristics may be hereditary ; of the latter class are instincts and the senses of color, 

 touch, light, hearing, smell, taste. A strong or weak memory is hereditary ; so also a 

 weak or powerful imagination, peculiarities of intellect, a violent temper or mild dis- 

 position, a strong or weak will, and finally idiocy or genius may run in families. 



In short, no vital phenomenon, physical or mental, is exempt from the law of hered- 

 ity, yet there are known exceptions, and by care in breeding the domestic animals, as 

 is well known, physical and moral defects can be eliminated, and in mankind good 

 judgment in marriage may result in visible improvement in the stock of certain 

 families. 



While the causes of heredity are unknown, attempts to account for them have been 

 made by various writers. Says Haeckel : " The cause of heredity is the partial iden- 

 tity of the materials which constitute the organism of the parent and child, and the 

 division of this substance at the time of reproduction." " Heredity," adds Ribot, " in 

 fact, is to be considered only as a kind of growth, like the spontaneous division of a 

 unicellular plant of the simplest organization." It is evident that in some of the con- 

 ditions of growth we may find an explanation of the fact of heredity. Another phys- 

 ical theory is that of ' pangenesis ' as proposed by Darwin, who conceives that cells, 

 before their conversion into ' form material,' throw off minute atoms which he calls 

 ' gemmules,' and which " may be transmitted from the parent to the offspring," and as 

 he claims, " are generally developed in the generation which immediately succeeds, 

 but are often transmitted in a dormant state during many generations and are then de- 

 veloped." Darwin's gemmules are entirely hypothetical, and, as Galton has observed, 

 the simple experiment of the transfusion of blood, by which a number of ' gemmules ' 

 would be inevitably transmitted from one individual to another without the usual 

 results as regards heredity, would seem to prove that pangenesis is " incorrect." Prof. 

 W. K. Brooks has, in his work on Heredity, restated the hypothesis, as he claims, "in a 

 form which is so modified as to escape this objection." 



Intimately connected with the subject of heredity is the fact of reversion or atavism, 

 where a child or young of any animal presents peculiarities evidently inherited not 

 from its parents, but from its grandparent or a remoter ancestor. Cases in point are 

 the occasional appearance, in horses, of stripes on the body and legs, which are supposed 

 by Darwin to have descended from a striped zebra-like ancestor. Darwin gives other 

 examples, and in human families certain traits are known to have jumped over one gen- 

 eration and to descend to the next. It is also a matter of observation that domestic 

 animals allowed to run wild tend to revert to their former feral condition. 



The third factor in evolution is 'natural selection.' Since the time of Laban, 

 herdsmen and stock-raisers have been able, by careful selection, matching those 

 cattle, horses, sheep, dogs, etc., which are pre-eminent in desirable qualities, such as 

 speed, size, draft, or, in the case of cows, good milking, either in quality or quantity. 



