246 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 
those occupying the same locality, or needing 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 confréres, 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: (1) 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 (1) 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 Eupagurus 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 
