NURTURE VERSUS NATURE 



acter mates with an organism in which the same 

 character is of an older type. The progeny all 

 give outward manifestation of the new character. 

 But their progeny show the recurrence of the old 

 character in one case in four, and two other mem- 

 bers of the four carry the factors for this quality 

 as a recessive element in their germ-plasm. If 

 the new character is beneficial to the species, the 

 individuals showing it (who in the second genera- 

 tion, it will be recalled, outnumbered their fel- 

 lows of the same fraternity three to one) will 

 thrive and propagate their kind, and the individ- 

 uals having the new quality will increase rapidly 

 in number. 



But meantime there is always a possibility that 

 the new character may be beneficial only under 

 local conditions or for a limited period ; so nature 

 is by no means minded to renounce the old char- 

 acter all at once. Generation after generation, 

 she provides that the factors for the recessive 

 traits shall be carried forward, and that a certain 

 proportion of the individuals of each generation 

 shall be " mixed dominants," whose offspring will 

 have representatives showing the old character. 

 So even when the new character is a highly bene- 

 ficial one, the old character still tends to recur and 

 to fight for recognition. 



But if, on the other hand, the new character is 

 one that is not beneficial, the individuals that 

 show it are quickly weeded out, and only the re- 

 cessive members of the fraternity remain. In 

 other words, a new or dominant character must be 



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