32 CHAPTER 2 | Genetics and Evolution
Today Darwinian natural selection can be defined as
the evolutionary process through which factors in the en-
vironment exert pressure, favoring some individuals over
others to produce the next generation. Darwin combined
his observations into the theory of evolution as follows: All
species display a range of variation, and all have the ability
to expand beyond their means of subsistence. It follows
that, in their “struggle for existence,” organisms with
variations to help them survive in a particular environment
will reproduce with greater success than others. Thus, as
generation succeeds generation, nature selects the most
advantageous variations and species evolve. So obvious
did the idea seem in hindsight that Thomas Henry Huxley,
one of the era’s most prominent scientists, remarked, “How
extremely stupid of me not to have thought of that.”^3
As often happens in the history of science, Darwin was
not alone in authoring the theory of natural selection. A
Welshman, Alfred Russel Wallace, independently came up
with the same idea at the same time while on a voyage to
the Malay Archipelago in Southeast Asia to collect speci-
mens for European zoos and museums. According to his
autobiography, a theory came to Wallace while he was in
a feverish delirium from malaria. He shared excitedly his
idea with other scientists in England, including Darwin,
whose own theory was yet unpublished. The two scientists
jointly presented their findings.
However straightforward the idea of evolution by nat-
ural selection may appear, the theory was (and has contin-
ued to be) a source of considerable controversy. Darwin
avoided the most contentious question of human origins,
limiting his commentary in the original work to a single
sentence near the end: “much light will be thrown on the
origin of man and his history.” The feisty Thomas Henry
Huxley, however, took up the subject of human origins ex-
plicitly through comparative anatomy of apes and humans
and an examination of the fossils in his book, On Man’s
Place in Nature, published in 1863.
Two problems plagued Darwin’s theory throughout
his career: First, how did variation arise in the first place?
Second, what was the mechanism of heredity by which
variable traits could be passed from one generation to the
next? Ironically, some of the information Darwin needed,
the basic laws of heredity, were available by 1866, through
the experimental work of Gregor Mendel (1822–1884), a
Roman Catholic monk, working in the monastery gardens
in Brno, a city in today’s Czech Republic.
Mendel, who was raised on a farm, possessed two particu-
lar talents: a flair for mathematics and a passion for garden-
ing. As with all farmers of his time, Mendel had an intuitivehad come to accept the idea that life had evolved, even
though they were not clear about how it happened. It re-
mained for Charles Darwin (1809–1882) to formulate a
theory that has withstood the test of time.
Grandson of Erasmus Darwin (a physician, scientist,
poet, and originator of a theory of evolution himself ),
Charles Darwin began studying medicine at the Univer-
sity of Edinburgh, Scotland. Finding himself unfit for this
profession, he went to Christ’s College, Cambridge Uni-
versity, to study theology. He then left Cambridge to take
the position of companion to British Royal Navy Captain
Robert FitzRoy on the H.M.S. Beagle, which was about
to embark on a scientific expedition to explore various
poorly mapped parts of the world. The voyage lasted for
almost five years, taking Darwin along the coasts of South
America, to the Galapagos Islands, across the Pacific to
Australia, and then across the Indian and Atlantic Oceans
to South America before returning to England in 1836.
Observing the tremendous diversity of living crea-
tures as well as the astounding fossils of extinct animals,
Darwin began to note that species varied according to the
environments they inhabited. The observations he made
on this voyage, his readings of Lyell’s Principles of Geology
(1830), and the arguments he had with the orthodox and
dogmatic FitzRoy all contributed to the ideas culminating
in Darwin’s most famous book, On the Origin of Species.
This book, published in 1859, over twenty years after he
returned from his voyage, described a theory of evolution
accounting for change within species and for the emer-
gence of new species in purely naturalistic terms.
Darwin added observations from English farm life and
intellectual thought to the ideas he began to develop on
the Beagle. He paid particular attention to domesticated
animals and farmers’ practice of breeding their stock
to select for specific traits. Darwin’s theoretical break-
through derived from an essay by economist Thomas
Malthus (1766–1834), which warned of the potential con-
sequences of increased human population, particularly of
the poor. Malthus observed that animal populations, un-
like human populations, remained stable, due to an over-
production of young followed by a large proportion of
animal offspring not surviving to maturity. Darwin wrote
in his autobiography, “It at once struck me that under
these circumstances favourable variations would tend to
be preserved, and unfavourable ones to be destroyed. The
results of this would be the formation of a new species.
Here, then I had at last got a theory by which to work.”^2
natural selection The evolutionary process through which
factors in the environment exert pressure, favoring some indi-
viduals over others to produce the next generation.(^3) Darwin, C. (1887). Autobiography. Reprinted in F. Darwin (Ed.). (1902),
The life and letters of Charles Darwin. London: John Murray.^3 Quoted in
Durant, J. C. (2000, April 23). Everybody into the gene pool. New York
Times Book Review, 11.
(^2) Darwin, C. (1887). Autobiography. Reprinted in F. Darwin (Ed.). (1902),
The life and letters of Charles Darwin. London: John Murray.