By Alfred Russel Wallace

Alfred Russel Wallace (1823-1913) is considered the co-discoverer with Darwin of the idea of evolution. It was once an essay which Wallace despatched in 1858 to Darwin (to whom he had devoted his most famed ebook, The Malay Archipelago) which impelled Darwin to submit a piece of writing on his personal long-pondered conception at the same time with that of Wallace. As a traveling naturalist and collector within the a ways East and South the United States, Wallace already susceptible in the direction of the Lamarckian concept of transmutation of species, and his personal researches confident him of the truth of evolution. at the book of at the beginning of Species, Wallace grew to become one in all its so much favorite advocates. This moment, corrected, version (1871) of a sequence of essays released in e-book shape in 1870, indicates the improvement of his wondering evolution, and emphasises his admiration for, and aid of, Darwin's paintings.

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The admitted facts^ seem to show that there has been a general, but not a detailed progression. Mollusca and Radiata existed before Vertebrata, and the progression from Fishes to Reptiles and Mammalia, and also from the lower mammals to the higher, is indisputable. On the other hand THE INTRODUCTION OF JSiJJV SPECIES. 15 it is said that the Mollusca and Eadiata of the very earliest periods were more highly organized than the great mass of those now existing, and that the very first fishes that have been discovered are by no means the lowest organised of the class.

Between these extremes the species will present various degrees of capacity for ensuring the means of preserving life; and it is thus we account for the abundance or rarity of species. Our ignorance will generally prevent us from accurately tracing the effects to their causes; but could we become perfectly acquainted with the D 34 ON THE TENDENCY OF VARIETIES TO DEPART organization and habits of the various species of animals, and could we measure the capacity of each for performing the different acts necessary to its safety and existence under all the varying circumstances by which it is surrounded, we might be able even to calculate the proportionate abundance of individuals which is the necessary result.

Why are the closely allied species of brown-backed Trogons all found in the East, and the green-backed in the West? Why are the Macaws and the Cockatoos similarly restricted ? Insects furnish a countless number of analogous examples;—the Goliathi of Africa, the OrnithopteraB of the Indian Islands, the Heliconidae of South America, the Danaidse of the East, and in all, the most closely allied species found THE INTRODUCTION OF NEW SPECIES. 13 in geographical proximity. The question forces itself upon every thinking mind,—why are these things so ?

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