1030 LIFE : OUTLINES OF GENERAL BIOLOGY 



the conclusion that marriage without "falHng in love" is prejudicial 

 to the race as well as to the individuals immediately concerned. 



(c) The increasing proportion of unmarried women in many civilised 

 communities is one of the serious problems of to-day. The outlook 

 will be even more grave if it be true (this we do not know) that 

 the ranks of the unmarried women contain a higher percentage of 

 eugenically desirable tjrpes, e.g. as regards intelligence, than is 

 found in a representative sample of the general female population. 



(d) On the other hand, as women attain to greater independence — 

 on economic and other foundations — sexual selection in mankind 

 will perhaps become better balanced. Whenever and wherever 

 women are able to give whole-hearted and effective preference to 

 the best available suitor, a eugenic lever of great power is at work. 



And may not what is so ancient, so manifest, and so increasing 

 a process in humanity, and by females of males as well as vice 

 versa, have also had its beginnings and even its not inconsiderable 

 developments in other species in the past? 



THE ISOLATION FACTOR IN EVOLUTION 



Lizards of the Dalmatian Islands. — ^As a typical instance of 

 the evolutionary interest of isolation we take Kammerer's careful 

 study of the lizards of the Dalmatian Islands. In earlier times 

 Italy and Dalmatia were united and that tract of country was in 

 all probability inhabited by a lizard which gave rise among others 

 to the modern species Lacerta serpa and L. fiumana. In some of 

 the islands which now mark the submerged area there are inter- 

 mediate forms which have not been markedly differentiated in 

 either direction. A reconstruction of what probably took place 

 indicates that L. serpa spread mainly to the south and west into 

 Italy and its Adriatic islands, while L. fiumana extended mainly 

 to the east and north into the Balkan region, where it gave 

 rise to L. taurica and L. ionica. At the present day Istria and 

 Dalmatia are inhabited by L. serpa and L. fiumana, which probably 

 spread from the North Adriatic area. On the whole, L. serpa fre- 

 quents the coast-lands and L. fiumana the interior, but there are 

 occasional encroachments of the one species into the other's 

 territory, though there is in such cases neither biological nor topo- 

 graphical mingling. There is often a lizardless neutral zone. 



From this mainland distribution that of the islands has followed. 



{a) When large islands were separated from the mainland, they 

 would contain L. serpa and L. fiumana (as is true to-day of Ugliana 

 and Veglia) or their common ancestor. 



{b) When small islands were separated from the coastal fringe, 

 whether of the mainland or of a large island, they would contain 



I 



