ALFRED RUSSEL WALLACE

Alfred Russel Wallace (1823–1913) was an explorer of the Amazon
Valley and led a zoological expedition to the Malay Archipelago,
which is an area of great biogeographical importance. Wallace,
like Darwin, was impressed with evolutionary change and had read
the writings of Thomas Malthus on human populations. In the
midst of a bout with malarial fever, he synthesized a theory of evolution
similar to Darwin’s theory of evolution by natural selection.
After writing the details of his theory, Wallace sent his paper to
Darwin for criticism. Darwin recognized the similarity of Wallace’s
ideas and prepared a short summary of his own theory. Both Wallace’s
and Darwin’s papers were published in the Journal of the Proceedings
of the Linnean Society in 1859. Darwin’s insistence on having
Wallace’s ideas presented along with his own shows Darwin’s
integrity. Darwin then shortened a manuscript he had been working
on since 1856 and published it as On the Origin of Species by
Means of Natural Selection in November 1859. The 1,250 copies
prepared in the first printing sold out the day the book was released.
In spite of the similarities in the theories of Wallace and
Darwin, there were also important differences. Wallace, for example,
believed that every evolutionary modification was a product
of selection and, therefore, had to be adaptive for the organism.
Darwin, on the other hand, admitted that natural selection may
not explain all evolutionary changes. He did not insist on finding
adaptive significance for every modification. Further, unlike Darwin,
Wallace stopped short of attributing human intellectual
functions and the ability to make moral judgments to evolution.
On both of these matters, Darwin’s ideas are closer to the views of
most modern scientists.
Wallace’s work motivated Darwin to publish his own ideas.
The theory of natural selection, however, is usually credited to
Charles Darwin. Darwin’s years of work and massive accumulations
of evidence led even Wallace to attribute the theory to
Darwin. Wallace wrote to Darwin in 1864:
I shall always maintain [the theory of evolution by natural
selection] to be actually yours and yours only. You
had worked it out in details I had never thought of
years before I had a ray of light on the subject.
Evolution is one of the major unifying themes in biology because
it helps explain both the similarities and the diversity of life.
There is no doubt that it has occurred in the past, and this chapter
describes the evidence of evolution and the historical development
of a theory that accounts for how evolution occurs.
Chapter 5 examines how the principles of population genetics
have been combined with Darwinian evolutionary theory into
what is often called the modern synthesis or neo-Darwinism.