The defenders were wrong. Louis Pasteur sealed the
fate of spontaneous generation in a series of careful experiments,
in 1861. He demonstrated clearly that microorganisms are carried
in the air, and that they grow in previously sterilized broths only
when the broths are contaminated by air or similar sources.
"All Life from Life" became one of the fixed
and immutable points of biological dogma. This led to a dilemma
that has been expressed as the chicken-and-egg paradox.
Which came first, the chicken or the egg? If all
eggs come only from chickens. and if all chickens come only from
eggs, then there must once have been either a first chicken or a
first egg. This demanded a Creator, a celestial clockmaker who at
least set the entire machinery of life in motion before stepping
back to let things take their "natural" course thereafter.
The operations of life and the mechanisms of life
hence were areas of fruitful research, but the origin of life was
not a legitimate subject for scientific investigation. Pasteur apparently
had disproved the only theory of the origin of life that was subject
to scientific testing.
While Pasteur was tamping the last dirt over the grave
of spontaneous generation, another extraordinarily important idea
was developing in biology - one that would not have its impact on
chemistry for nearly a century. This was the theory of evolution,
as proposed by Charles Darwin, Alfred Wallace, and the very able
propagandist, Thomas Huxley.