E. Morselli.,Biology and Eugenics.61 
are of a complicated order; some depend upon its position in space, others 
are mixed up with the history of the same race and population in relation 
with other races. 
(iv.) All the characters of a human variety or race persist as long as 
its mesological adaptation lasts. They vary with the modification of its 
conditions of life. Hence, the displacements in space, whether forced or 
voluntary, and the relations with other races are the causes of the modifications 
and transformations to which ethnic types are subjected in historic times, 
deduction being made for the slower effects of physical and geographical 
changes. (v.) There is a hierarchy of the human varieties and races, whether from 
the static point of view of their morphology and psychology, or from the 
dynamic point of view of their predominance and their dissolution in 
mixed unions. It is always the races strongest biologically and most 
evolved psychologically which impress their characters upon the descendants 
of these unions. This fact renders difficult the formation of truly mongrel 
or hybrid races. The metamorphosis of ethnic types is understood in a 
very restricted sense. 
(vi.) A certain degree of difference amongst the parent varieties or 
races is necessary for the vitality and the prosperity of mixed or metamorphic 
populations : nevertheless, too great a difference, besides rendering unions 
more difficult for moral rather than for physical reasons, proves always 
injurious to the descendants as much in physique as in mind. 
(vii.) Mixed unions exert the same influences upon the mental characters 
of race as can be observed in bodily characters : (a) In the descendants will 
be found the same mixture of the capacities aptitudes and psychical tendencies 
of the parent races; (b) a combination may occur of the same characters 
with the formation of intermediate mental qualities : (c) there are sometimes 
psychical racial qualities which become “ dominant ” according to the well- 
known “ law of Mendel.” 
(viii.) Every race, people, and nation, being the product of an adapta­ 
tion, whether through the action of external factors, or in consequence of 
its historic vicissitudes, all ethnic groupings develop, live, prosper, and dis­ 
appear according to the same laws which regulate the fortunes of other 
living beings; all have their destiny marked out by the stage to which they 
have attained in the psycho-physical hierarchy of man. 
(ix.) It is needful that every race, or population, or nation, when it has 
acquired the consciousness and the feeling for its own distinctive characters 
and of the part which awaits it in the development of universal civilisation, 
should contemplate the preservation of its own ethnic type. The differentia­ 
tion of peoples is one of the causes, if however not the chief cause, of 
progress in human evolution. 
(x.) The Science of Eugenics, which has for its chief end the establish­ 
ment of means for bringing the species to perfection, ought not to look only