152 SOCIAL EVOLUTION 



The topography of an inhabited region, besides deter- 

 mining the direction and destination of migrations or 

 furnishing protection from the assaults of hostile peo- 

 ples, often results in the more or less complete isolation 

 of a people from the progressive or retarding influences 

 acting upon the general population without the shel- 

 tered valley or far from the lonely island. 



Isolation prohibits much intermixture of different 

 stocks. This tends to accentuate traits already existing 

 in the stock, as potential possibilities. Sometimes de- 

 fects, intensified and inherited, appear with great 

 frequency. Dr. Alexander Graham Bell made a careful 

 genealogical study of western Martha's Vineyard and 

 found that there had been a great deal of intermarrying 

 and a great many consanguineous marriages. The lo- 

 cality is inhabited by farmers and fishermen of average 

 intelligence and good character. Deaf mutes are strik- 

 ingly numerous. In 1880 there was a proportion of 1 

 to 25 of the whole population affected.^ ^ Further south 

 along the Atlantic coast there are beaches or banks some 

 distance from the mainland. Here there are many con- 

 sanguineous marriages. A wide-spread trait that may 

 be ascribed to this inbreeding is suspicion and mental 

 dullness; and a relatively high frequency of insanity.^*^ 

 Over sixty-six per cent, of the population of Sardinia are 

 brunettes. Whereas, brunettes on the continental penin- 

 sula of Italy range from thirty-eight per cent, to over 

 sixty-six per cent, of the total population. This shows 

 how the pure color traits of the stock have been preserved 

 by isolation.^^ 



3.S Davciijioil, ('. V,.—IIci((lil!J in UchitUm to Eufjcnlcs, l'.)ll, y]K 101- 

 1!)2. 



■■i-> Ibid., p. V.)o. ^" Kiplcv, W. 'A.— Tin: h'uv.fi of luiruiic, y, -.ioU.^ 



