SCIENCE. 



301 



BOOKS RECEIVED. 



Island Life; Or, The Phenomena and Causes of 

 Insular Faunas and Floras, including a revision 

 and attempted solution of the Problem of Geological 



. Climates, by Alfred Russel Wallace. — Harper 

 Brothers, New York, 1881. 



The authors of the theory of evolution undoubtedly feel 

 the responsibility involved in revolutionizing one of the 

 most important branches of Science ; it is therefore natural 

 to find both Dr. Darwin and Mr. Wallace devoting their 

 best energies to aid evolutionists in placing "the theory " 

 upon a sound basis. 



Perhaps one of the strongest arguments that can be 

 advanced in favor of evolution is the fact, that it offers a 

 key for solving difficulties encountered by naturalists, 

 which hitherto were inexplicable, or accounted for by a 

 line of reasoning now shown to be erroneous. 



The distribution of animal life upon the globe, which 

 forms the subject of the present work, exhibits in a strong 

 light some of the fallacies of the older naturalists, and the 

 value of the theory of evolution in interpreting the work 

 of Nature. 



The old school of naturalists explained the geographi- 

 cal distribution of animals by believing, that " the several 

 species of animals and plants " were special creations, 

 and consequently assumed, that every animal was exactly 

 adapted to the climate and surroundings amid which it 

 lived, and that the only, or, at all events, the chief reason 

 why it did not inhabit any other country was that the 

 climate or general condition of that country was not 

 suitable to it. 



In the present state of knowledge respecting the fauna 

 and flora of the whole world, it is not difficult to prove 

 that other reasons must be found to account for the 

 phenomena met with in the general distribution of ani- 

 mal life, and Mr. Wallace makes the case quite clear by 

 giving some striking illustrations. 



It is true that hot climates differ from cold ones in all 

 their organic forms, but its effects are by no means con- 

 stant, but are irregular and uncertain, and the contrast 

 does not bear any proportion to the difference of tem- 

 perature. 



For instance, between frigid Canada and sub-tropical 

 Florida there are less marked differences in the animal 

 productions than between Florida and Cuba or Yucatan, 

 which are much more alike in climate and so much 

 nearer together. So the differences between the birds 

 and quadrupeds of temperate Tasmania and tropical 

 North Australia are slight and unimportant as compared 

 with the ^normuus differences we find when we pass from 

 the latter country to equally tropical Java, and if we com- 

 pare corresponding portions of different continents, we 

 find no indications that the almost perfect similarity and 

 general conditions have any tendency to produce similarity 

 in the animal world. The equatorial parts of Brazil and 

 of the west coast of Africa are almost identical in climate 

 and in luxuriance of vegetation, but their animal is 

 totally diverse. In the former we have tapirs, sloths, and 

 prehensile-tailed monkeys ; in the latter, elephants, ante- 

 lopes, and man-like apes ; while among birds, the tou- 

 cans, chatterers and humming-birds of Brazil, are re- 

 placed by the plantation-eaters, bee-eaters and sun birds 

 of Africa. Parts of South-temperate America, South 

 Africa and South Austalia correspond closely in climate ; 

 yet the birds and quadrupeds of these three districts are 

 as completely unlike each other as those of any parts of 

 the world that can be named. The present work, 

 although complete in itself, is one. of a series prepared by 

 Mr. Wallace to account for the geographical distribution 

 of animal life, by the theory of evolution, and being the 

 result of many years study by one of the most eminent 

 of living naturalists, will command the attention of all who 

 desire to find a true solution of the subject. 



Some of the most remarkable and interesting facts in > 



the distributions and affinities of organic forms are pre- 

 sented by islands in relation to each other and to the sur- 

 rounding continents. Yet their full importance in connec- 

 tion with the history of the earth and its inhabitants has 

 hardly yet been recognized ; and in order to direct the 

 attention of naturalists to this most promising field of re- 

 search, Mr. Wallace has restricted himself in the volume 

 now before us, to the elucidations of some of the prob- 

 lems there presented to us. 



Such then is the scope and purpose of " Island Life, or 

 the Phenomena and Causes of Insular Faunas and 

 Floras," involving the study of a class of subjects em- 

 bracing in their very nature the visible outcome and 

 resudical product of the whole past history of the earth. 

 There is no royal road to the acquisition of knowledge, 

 and to prepare those readers who have not been trained 

 in such studies to appreciate the conclusions drawn, 

 Mr. Wallace in the first eight chapters devotes much 

 space to the explanation of the mode of distribution, 

 variation, modification and dispersal of species and 

 groups, illustrated by facts and examples ; of the true 

 nature of geological change as affecting continents and 

 islands ; of changes of climates, their nature, causes and 

 effects ; of the duration of geological time and the rate 

 of organic development. 



The aim of Mr. Wallace in this work is the develop- 

 ment of a clear and definite theory, and its applica- 

 tion to the solution of a number of biological problems. 

 That theory may be briefly stated as follows : That 

 the distribution of the various species and groups of 

 living things over the earth's surface, and their aggre- 

 gation in definite assemblages in certain areas, are the 

 direct result and outcome of a complex set of causes, 

 which may be grouped as "biological" and "physi- 

 cal." The biological causes are mainly of two kinds — 

 first, the constant tendency of all organisms to increase 

 in numbers, and to occupy a wider area, and their 

 various powers of dispersion and migration through 

 which, when unchecked, they are enable to spread 

 widely over the globe ; and secondly, those laws of evolu- 

 tion and extinction which determine the manner in which 

 groups of organisms arise and grow, reach their maxi- 

 mum, and then dwindle away, often breaking up into 

 separate portions which long survive in very remote 

 regions. The physical causes are mainly of two kinds. 

 We have, first, the geographical changes which at one 

 time isolate a whole fauna and flora, at another 

 time lead to their dispersal and intermixture with 

 adjacent faunas and floras, and here Mr. Wallace 

 endeavored to ascertain and define the exact nature and 

 extent of these changes, and to determine the question 

 of the general stability or instability of continents 

 and oceans ; in the second place he also investigated 

 the exact nature, extent and frequency of the changes of 

 climate which have occurred in various parts of the 

 earth, because, as it may be supposed, such changes are 

 among the most powerful agents in causing the dispersal 

 and extinction of plants and animals. The importance 

 attached to the geological climates and their causes, 

 induced Mr. Wallace to discuss this branch of the sub- 

 ject at some length, and the most recent investigations 

 of geologists, physicists and explorers were fully called 

 into requisition. 



Mr. Wallace next applied these facts and theories to 

 explain the phenomena presented by the floras and faunas 

 of the chief islands of the globe, which are classified, in 

 accordance with their physical origin, in three groups 

 or classes, each of which is shown to exhibit certain well 

 marked biological features. 



Mr. Wallace then defines what'are called "areas of 

 distribution" as applied to species, genera and families, 

 and, taking British mammals and land birds, he follows 

 them over the whole area they inhabit, and obtains a 

 foundation for the establishment of " zoological regions," 

 1 and a clear insight is formed of their character as dis- 



