246 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 



those occupying the same locaHty, or needmg the same food, or needing 

 each other as food; (2) the probable success in this competition of 

 those individuals whose slight differences (variations) are of such a 

 nature as to give them an advantage over their confreres, which 

 results in saving their life, at least until they have produced offspring; 

 and (3) the fact that these "saved" individuals will, by virtue of the 

 already referred to action of heredity, hand down to the offspring 

 their advantageous condition of structure and physiology (at least, as 

 the ''mode" or most abundantly represented condition, among the 

 offspring). 



The competition among individuals and kinds (species) of organ- 

 isms may fairly be called a struggle. This is obvious when it is active, 

 as in actual personal battling for a piece of food or in attempts to 

 capture prey or to escape capture, and less obvious when it is passive, 

 as in the endurance of stress of weather, hunger, thirst, and untoward 

 conditions of any kind. The struggle is, or may be, for each individual 

 threefold in nature: (i) an active struggle or competition with other 

 individuals of its own kind for space in the habitat, sufficient share of 

 the food, and opportunity to produce offspring in the way peculiar 

 and common to its species; (2) an active or passive struggle or compe- 

 tition with the individuals of other species, which may need the same 

 space and food as itself, or may need it or its eggs or young for food; 

 and (3) an active (or more usually passive) struggle with the physico- 

 chemical external conditions of the world it lives in, as varying 

 temperature and humidity, storms and floods, and natural catas- 

 trophes of all sorts. For any individual or group of individuals any of 

 these forms of struggle may be temporarily ameliorated, as is (i) the 

 intra-specific struggle among the thousands of honey-bee individuals 

 living together altruistically, in one hive, or (2) the inter-specific 

 struggle, when two species live together symbiotically as the hermit 

 crab Eupa gurus and the sea-anemone Podocoryne, or (3) the struggle 

 against untoward natural conditions as in special times or places 

 of highly favourable climate, etc. Or for any individual or group 

 of individuals all forms of the struggle may be coincidently active 

 and severe. The resultant of these existing conditions is, accord- 

 ing to Darwin and his followers, an inevitable natural selection of 

 individuals and of species. Thousands must die where one or ten 

 may live to maturity (i.e., to the time of producing young). Which 

 ten of the thousand shall live depends on the slight but sufficient 

 advantage possessed by ten individuals in the complex struggle for 



