GEOGRAPHIC DISTRIBUTION OF ANIMALS: OCEANIC ISLANDS 287 



150 miles north and east of its nearest neighbojv_Eitcairn. Henderson is 

 about 2.5 by 5 miles in extent; its greatest elevation is betweeiT75 and 100 

 feet above sea level. It is certainly a young island, its age numbered in 

 thousands of years rather than in hundreds of thousands. It appears to have 

 risen sterile from the sea, hke the island shown in Fig. 13.1. Zimmerman 

 recorded that today it is densely covered with tangled tropical jungle. The 

 Bishop Museum expedition of 1934 found more than 250 species of plants, \ / 

 mostly native, as well as an endemic genus or subgenus of rail, endemic 

 insects, and endemic land snails. (Endemic species, genera, etc., are those 

 occurring nowhere else than in the region under discussion.) Zimmerman \ 

 concluded, "Thus, all of the major elements of the Polynesian terrestrial 

 biota have succeeded in being transported across the sea, colonizing this 

 tiny bit of isolated land, and have not only established themselves there but 

 have evolved into new forms quite distinct from their forebears." | 



Thus far in our discussion of oceanic islands we have summarized the 

 general characteristics of their animal life and discussed the means by 

 which animals reached them. With these facts in mind we shall now turn 

 our attention to a particular group of islands which have long held special 

 interest for biologists, partly no doubt because it was the peculiarities of the 

 animals inhabiting these islands which gave impetus to Darwin's thinking 

 upon the subject of evolution. We refer to the Galapagos Islands, which 

 Darwin visited in 1835 in connection with his circumnavigation of the 

 globe as naturahst on H.M.S. Beagle. 



GALAPAGOS ARCHIPELAGO 



The Galapagos archipelago is located on the equator 

 about 600 miles west of South America (Fig. 13.2). There are five large / 

 islands in the group, with nineteen smaller ones and forty-seven rocks. The 

 islands are of volcanic origin; some of the volcanoes are still active. The 

 topography is rough and mountainous, the highest mountain rising more 

 th an 40 00 feet above the sea. The lower regions of the islands are dry and 

 barren, with a rough, inhospitable surface reminding visitors of an un- 

 finished planet. Darwin (1839) wrote, "Nothing could be less inviting 

 than the first appearance. A broken field of black basaltic lava, thrown 

 into the most rugged waves, and crossed by great fissures, is every where 

 covered by stunted, sunburnt brushwood, which shows little signs of life." 

 Elsewhere he expressed himself still more feelingly: "The country was 

 compared to what we might imagine the cultivated parts of the Infernal 



