368 C. SKOTTSBERG 



intensity of divergence will be increased". It is not clear to me why the intensity 

 would be increased. Now, if sufficient time has elapsed and the original sources 

 lia\e been eroded down and perhaps become sterile atolls, their faunas will have 

 been exterminated and on the newer islands segregates without obvious ancestral 

 relation will be left. This development explains why Hawaii has so many isolated 

 endemic t\'pes. The living world in Hawaii is older than the rock — in a way, he 

 sa)-s. ( )uite true, but it is not true that this possibility has, as he says, been entirely 

 o\erl()oke(l in previous discussions; I think that 1 have, on repeated occasions, 

 exj)ressed myself ver\' clearly on this point, even if 1 do not agree with ZIMMERMAN 

 when it comes to exj)lain why and how it happened. 



The biota as we know it today is in part the ultimate product of a progressional 

 devclopnient which has moved and evolved along great insular archipelagos over periods 

 of time much longer than the ages rec^uired for the development of the main Hawaiian 

 Islands and their contemporary biota. Various genera and stem forms of groups of species 

 iiKu have evolved in islands — now atolls such as some of the leeward Hawaiian chain, 

 the great Micronesian archi])elagos, the Line Islands — which form the approach to Hawaii. 

 However, some of the genera and the bulk of species known today have originated on 

 our present main islands (p. 125) ... in contemporary Hawaii there are preserved rem- 

 nants of a biota which has in ])art develoj)ed by unique methods and in which are preserved 

 forms whicli are the end ])roducts of species chains that carry back, through archi- 

 ])elagos now worn away, to geological ages indeterminant (p. 126). 



In few words, we have to do with relict as well as progressive endemism — 

 nobody objects to that. A genus may be an ancient relic, while the actual species 

 are the result of more recent, progressive differentiation. On the other hand, there 

 is no reason why not a species could be immensely old without having undergone 

 any j)crceptible change. 



Zimmi:rm.\x does not hesitate to conjure up all the sunk archipelagos he needs, 

 if only land connections arc left out of the discussion. Once more he describes 

 his vision on p. 127 which I shall permit myself to quote, with the obvious risk 

 of tiring out the reader. 



I believe that the great atoll chains of the Pacific may hold some of the now hidden 

 (lues to the stories of the magnificent biological development of Polynesia. Many of the 

 peculiar endemic groups of the Hawaiian and southeastern Polynesian islands owe their 

 existence, if not their very origin, to ancient high islands of the one-time splendid archi- 

 l)clagos marked by (lusters or coral reefs. Surviving lines of middle Tertiary and of 

 |)erhaj)s even older continental faunas nuiy have had their germ plasm filtered down 

 through su( cessivcly changing generations which have passed successfully through island 

 maturity and degradation to atoll formation and have carried over to new high islands 

 in different archipelagos. Thus, some supposedly old types such as certain land molluscs 

 could have maintained themselves (but evolving) in insular isolation through long periods 

 ot time while tlieir continental j)rogenitors became extinct or restricted under continental 

 conditions. 



I cannot think of what kind of higher organisms would have passed success- 

 fully through island degradation down to atoll stage; they must have left for new 

 high islands long before their abode became uninhabitable. V.ven if, as ZIMMERMAN 

 thinks, much of the evolution took place during migration from island to island, 



