It is generally accepted that prese

It is generally accepted that present-day animals and plants differ from those of the
past, (0) ...having ... changed by a general process called evolution. But this theory has been widely accepted for little (1) ................ than a hundred years. The present theory of evolution was
developed (2) ................ two naturalists – Charles Darwin and Alfred Russell Wallace – working independently.
When he was a young man (3) ................ 22, Darwin went as naturalist on a round-the-world, map-making cruise aboard a British naval survey ship, HMS Beagle. The cruise began in 1831 and lasted (4) ................ 1836. In the Galapagos islands, Darwin came (5) ................ a group
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of birds, later to become known (6) ................ “Darwin’s finches”. They were similar to one (7) ................ in their colour, song, nests and eggs, and were clearly descended (8) ................ the same finch stock, (9) ................ each had a different kind of beak and was adapted (10) ................ a different way of life. (11) ................ were seed-eaters, fly-catchers, woodpeckers and various other types.
Darwin assumed that the ancestors of all (12) ................ types had been blown to the islands in bleak weather, had survived and changed somehow (13) ................ the various forms. In the years after the voyage, Darwin gradually came to the conclusion that individuals better suited (14) ................ their environment would tend to leave more offspring while those (15) ................ well adapted would die out.