282 INTRODUCTION TO EVOLUTION 



ward until it becomes a towering mountain rivaling Mauna Kea in the 

 / Hawaiian group. Mau na Kea rises^ 31 ,75QJeet above the ocean floor and 

 ' hence is the world's highest mountain, measured from base to summit. 



How Oceanic Islands Are Populated 



What animals and plants inhabit oceanic islands? The latter are popu- 

 lated by forms able to reach them by means other than passage across dry 

 land. This statement follows from our definition of an oceanic island (p. 

 280). We must hasten to add, however, that there have been in the past, 

 and are today, students of island life who believe that many of the islands 

 usually considered_oce^nic nevertheless at one time or another were con- 

 nected to continents, either by land bridges~or by having actually consti- 

 tuted a portion of the continent. According to the latter view the island 

 subsequently became detached from the continent and drifted away from it. 

 This would be a very difl'erent method of oceanic island formation from 

 the one described above. It forms part of the theory ofJ^CDOtiflefitaLddftj'^ 

 according to which all the continents and islands at one time were gathered 

 together into one continuous land mass. Eventually the parts of this mass 

 separated from each other and drifted away, leaving the oceans in between. 



The whole matter is highly controversial; evidence for and against each 

 theory would be out of place in an elementary discussion (see Darlington, 

 1957, pp. 606-613). The author will assume responsibility for the state- 

 ment that the evidence for such drift is to his mind unconvincing, being 

 derived mainly, not from the researches of geologists, where one would 

 naturally look for it, but from the researches of students of plant and 

 animal distribution. Some students of distribution find explanation of ob- 

 served facts difficult without assuming the occurrence of such original 

 unity and subsequent separation of the land masses of the earth. Since, 

 however, there are still many unknown factors involved in the dispersal of 

 animals and plants, it seems wiser to admit gaps in our knowledge of 

 how living things reach out-of-the-way places, and to seek to fill those 

 gaps, than it is to postulate movements of continents and islands like pieces 

 on a chessboard. This postulate may form an easy way out of a dilemma, 

 but the easy way is frequently not the correct way. 



Accordingly, our discussion of the means by which oceanic islands re- 

 ceive their inhabitants will dispense with floating continents, as well as 

 with land bridges and sunken or "lost" continents sometimes postulated 

 where vast depths of ocean are now found. We fully realize that some 

 students of the subject will disagree with us. 



