CHAPTER TWENTY. 

 RELATIONS OF PARENTS AND OFFSPRING. 



1. Review. In Chapter Eight we studied these relations 

 in some of the lower plants and animals. We found that 

 reproduction is always a sacrifice on the part of the 

 parent; that this sacrifice is necessary to keep the species 

 going; that the parent is completely destroyed in the 

 lowest forms of reproduction, as fission; and that the 

 parent can economize by giving a smaller part of itself 

 to each offspring. Thus we saw a reduction in the amount 

 of substance which went into each offspring. 



2. What Parents Must Do. Just the same problems 

 confront the parent in the higher forms as were discovered 

 in the lower. Two parents must, on the average, bring to 

 maturity two offspring during their own life time in order 

 to keep the race where it now is. The problem of parents 

 is to hit upon the best way to do this. It is for the good 

 of the race that the parent shall not be used up in this 

 sacrifice until enough offspring have been produced to 

 allow two to survive the disasters that confront them. 

 On the other hand, the parent must sacrifice enough 

 matter and energy in reproduction to insure the species. 



3. Condition in Higher Organisms. In the higher plants 

 and animals we have found two methods of reproduction 

 that are peculiarly prevalent: reproduction by spores, and 

 reproduction by gametes. In both of these methods the 

 offspring consists of a single cell, whereas the adult may 

 include millions of cells. Thus the ratio of the offspring to 



107 



