Evolution__3rd_Edition

10 PART 1 / Introduction
. . . looked for a mechanism ...
. . . and discovered natural
selection
a crucial fact a adaptation. His theory would have to explain not only why species
change, but also why they are well designed for life. In Darwin’s own words (in his
autobiography):
It was equally evident that neither the action of the surrounding conditions, nor the will of
the organisms [an allusion to Lamarck], could account for the innumerable cases in which
organisms of every kind are beautifully adapted to their habits of life a for instance a
woodpecker or tree-frog to climb trees, or a seed for dispersal by hooks or plumes. I had
always been much struck by such adaptations, and until these could be explained it
seemed to me almost useless to endeavour to prove by indirect evidence that species have
been modified.
Darwin came upon the explanation while reading Malthus’s Essay on Population. He
continued:
In October 1838, that is fifteen months after I had begun my systematic enquiry, I
happened to read for amusement ‘Malthus on population’, and being well prepared to
appreciate the struggle for existence which everywhere goes on from long-continued
observation of the habits of animals and plants, it at once struck me that under these circumstances
favourable variations would tend to be preserved and unfavourable ones to be
destroyed. The result of this would be the formation of a new species.
Because of the struggle for existence, forms that are better adapted to survive will
leave more offspring and automatically increase in frequency from one generation to
the next. As the environment changes through time (for example, from humid to arid),
different forms of a species will be better adapted to it than were the forms in the past.
The better adapted forms will increase in frequency, and the now poorly adapted forms
will decrease in frequency. As the process continues, eventually (in Darwin’s words)
“the result of this would be the formation of a new species.” This process provided
Darwin with what he called “a theory by which to work.” And he started to work. He
was still at work, fitting facts into his theoretical scheme, 20 years later when he received
a letter from another traveling British naturalist, Alfred Russel Wallace (Figure 1.4).
Wallace had independently arrived at a very similar idea to Darwin’s natural selection.
Darwin’s friends, Charles Lyell and Joseph Hooker (Figure 1.5a), arranged for a simultaneous
announcement of Darwin and Wallace’s idea at the Linnean Society in London
in 1858. By then Darwin was already writing an abstract of his full findings: that
abstract is the scientific classic On the Origin of Species.
1.3.3 Darwin’s reception
The reactions to Darwin’s two connected theories a evolution and natural selection a
differed. The idea of evolution itself become controversial mainly in the popular sphere
only, rather than among biologists. Evolution seemed to contradict the Bible, in which
the various kinds of living things are said to have been created separately. In Britain,
Thomas Henry Huxley (Figure 1.5b) particularly defended the new evolutionary view
against religious attack.
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