100 HEEBDITY AND SELECTION IN SOCIOLOGY 



be checked before they become excessive — ^that is to say, before 

 they attain biological value. Thus we see that amphimixis is 

 always and at all times a necessary factor in maintaining the 

 steady and constant adaptation of a species at every moment of 

 its existence. As adaptation is synonymous with organic life — 

 for we cannot imagine life which is non-adapted — and as amphi- 

 mixis, where it exists, is the chief factor in effecting and con- 

 solidating adaptation, we can understand that the determinants 

 of amphimixis are very stable — even more stable than the specific 

 determinants of the species. 



What we have said enables us to understand that amphimixis 

 has especial importance as an equaliser of differences, as a 

 guarantee of the constancy of the species. Through the unin- 

 terrupted activity of amphimixis, we get a centre-point which 

 represents the biological average of a given species, around which 

 are to be found concentrated the great majority of the members 

 of that species ; while the variations which diverge from the 

 biological average become less and less numerous as they approach 

 the limits of the possible vital conditions of the species. For 

 instance, to take only one characteristic, the height of the human 

 body varies around an average, the variations becoming less and 

 less numerous according as they diverge further and further from 

 this average, until finally the limit of the biological conditions is 

 reached, beyond which no human Ufe is possible. As height is 

 not a very vital characteristic, it does not show a narrow " varia- 

 tion limit " — to use Ammon's expression^ — but it is obvious that 

 too small a dwarf or too gigantic a giant could not survive. 



Galton has particularly insisted on this tendency of amphi- 

 mixis to establish a centre-point, or biological average, represent- 

 ing the general character of the species, personified by the majority 

 of that species. We may represent this tendency of amphimixis 

 by any curve (Fig. 5). C represents the lowest, D the highest, 



1 0. Ammon, Der Abdnderungsspidraum, in NaturmssmschafUiehe 

 Wochenschrift. Berlin, Nos. 12-14, 1896. 



