Pre-Darwinian Theories

was Darwin's book, rather than Wallace's
essay, that had the most impact on the
Victorian public. Darwin not only described
the process of natural selection in more detail,
but he also gave numerous examples of it. It
was his On the Origin of Species that convinced
most educated people in the late 19th century
that life forms do change through time. This
prepared the public for the acceptance of
earlier human species and of a world much
older than 6000 years.
Darwin and Victorian Culture--interview with
Darwin's biographer, James Moore
This link takes you to an audio file at an
external website. To return here, you must click
the "back" button on your browser
program. (length = 8 mins, 5 secs)
Both Darwin and Wallace
failed to understand an
important aspect of natural
selection. They realized that
plant and animal
populations are composed of
individuals that vary from
each other in physical form.
They also understood that
nature selects from the
existing varieties those traits
that are most suited to their
Gregor Mendel
1822-1884
environment. If natural selection were the only
process occurring, each generation should have
less variation until all members of a population
are essentially identical, or clones of each
other. That does not happen. Each new
generation has new variations. Darwin was
aware of this fact, but he did not understand
what caused the variation. The first person to
begin to grasp why this happens was an
obscure Central European monk named
Gregor Mendel . Through plant breeding
experiments carried out between 1856 and
1863, he discovered that there is a