Page images

ductions of species which take place by human agency) are stocked only with such animals and plants as could have been transported, either fullgrown, or as seeds or eggs, by the waters of the ocean, by the winds, or by birds.

Only a very few illustrations of the laws just stated can here be given; but it is important that the reader should understand that none of the kinds of evidence in favor of evolution loses more by being represented only by scattered instances than does the argument from distribution. Of the first principle above given, Australia, Madagascar, and South America are striking examples. The Australian fauna, for instance, contains few maminals except those of the lowest orders (the montremes 1 and the marsupials 1); and the absence of the dog, the cat, the deer, and the monkey family, and of the groups of animals allied to these, gives to the fauna of the country such an aspect of antiquity as has not existed in the more northerly continents since the reptilian age. Now, Australia is separated from the nearest mainland by some fifteen hundred iniles of sea; Madagascar is cut off from Africa (to which it once belonged by the great Mozambique Channel, two hundred and fifty miles wide, and in some places over nine thousand feet deep; South America is united to North America only by a slender isthmus, and even this was sunk beneath the sea during some part of the age of mammals.

1 See Appendix.

In illustration of the second principle, we may compare the fauna of the British Isles with that of Europe, and the fauna of Madagascar with that of Africa. The comparison is a good one to make; for Madagascar has been separated from Africa since about the close of the age of mammals, while the British Isles have certainly remained part of the European continent till well into the age of man. In regard to the fauna of the British Isles, Wallace says, —

“ All the higher and more perfectly organized animals are, with but few exceptions, identical with those of France and Germany. 1

In Madagascar, on the other hand, speaking of the mammals, Wallace says,

“ The character of these animals is very extraordinary, and very different from the assemblage now found in Africa or any other existing continent. Africa is now most prominently characterized by its monkeys, apes, and baboons, by its lions, leopards and hyenas, by its zebras, rhinoceroses, elephants, buffaloes, giraffes, and merous

1 Island Life, p. 313.

species of antelopes. But no one of these animals, nor any thing like them, is found in Madagascar; and thus our first impression would be, that it never could have been united with the African continent. But as the tigers, the bears, the tapirs, the deer, and the numerous squirrels of Asia, are equally absent, there seems no probability of its ever having been united with that continent.” 1

In illustration of the third principle, the Sandwich Islands offer themslves as the best example of strictly oceanic islands, situated as they are twenty-three hundred and fifty miles from the nearest mainland (the coast of California), and with the nearest group of islands six hundred or seven hundred miles distant. No land mammal nor amphibian could travel by sea over such vast distances as these, and accordingly no member of either of these great classes of animals is found native in the islands. Their birds, too, largely belong to the orders of waders, swimmers, and birds of prey, — all groups marked by great powers of flight. No other vertebrates are found native, excepting two lizards. Of the remaining animals, the most distinctive are the land-shells already mentioned; and of these there are between three hundred and four hundred known species, all of them peculiar to the Sandwich Islands. Vegetation is abundant; but more than three-fifths of the plants are confined to these islands, and there is an immensely large proportion of ferns. Among the flowering plants I do not notice one in the list quoted by Wallace which has a heavy, perishable seed (like acorns, most nuts, and so on); while the family which embraces the most species is one 1 whose seeds are frequently carried great distances by the wind.

1 Island Life, p. 381.

The ancestors of the numerous snails of these islands may have been very few in number; since the first immigrants to so promising a field would have had an unusually good opportunity to multiply, and in multiplying they may well enough have varied so as at length to produce all the present species. The eggs of these snails were probably first brought to the Sandwich Islands on the feet of birds, in a manner first suggested by Mr. Darwin.

Birds, too, may well have brought many of the seeds of plants, some in their crops, and others clinging to the mud on their feet.

The spores ? of ferns are as fine as dust, and mulcitudes of these may have been carried to the islands by the wind. How the lizards of the Sandwich Islands reached their present home is unknown;1 there are sufficient grounds for believing that these animals are possessed of some as yet undiscovered means of travelling for great distances by water.

i The Compositæ, or family of compound flowers, like the. daisy, aster, thistle, and so on.

2 Little bodies answering the purpose of seeds.

What bearing the facts and principles just given have on the development theory may be best shown by stating what laws we should expect to find governing the distribution of animals and plants, if the innumerable species were the result of acts of creation, in the ordinary sense of the term. If this were the case, we might reasonably expect :

1. That new species of modern forms would appear just as largely in separated lands as in the great connected land-masses. For, if the new species are supposed to be made in conformity with geological changes in the earth's surface, they should be as frequent in the separated as in the connected lands; since such changes are more frequent, as a rule, in the former than in the latter. Or, if the supposed creations were purposeless, they would be as likely to occur in one place as in another.

2. Creations (if wisely adjusted to the conditions of animal and of plant life) should in sepa

1 Island Life, p. 265.

« PreviousContinue »