"It was the science of geology that first cast serious doubt on the biblical account of special creation for each animal species, as it became clear that there had in the past been great changes in rocks, and so in the environment, and yet animals were adapted to the present environment. It also became clear that the age of the earth was very much greater than the biblical account taken literally allows; and, perhaps most important, unknown forms of life were discovered as fossils."
Jean-Baptiste De Lamarck (1744-1829)
"In mid-eighteenth century the biological world looked like
this: there was a supreme mind at the top of the ladder, which
was the basic explanation of everything downwards from that--the
supreme mind being, in Christianity, God; and having various attributes
at various philosophic stages. The ladder of explanation went
downwards deductively from the Supreme to man to the apes, and
so on, down to the infusoria.
This hierarchy was a set of deductive steps from the most perfect to the most crude or simple. And it was rigid. It was assumed that every species was unchanging.
Lamarck, probably the greatest biologist in history, turned that ladder of explanation upside down. He was the man who said it starts with the infusoria and that there were changes leading up to man. His turning the taxonomy upside down is one of the most astonishing feats that has ever occurred. It was the equivalent in biology of the Copernican revolution in astronomy.
The logical outcome of turning the taxonomy upside down was that the study of evolution might provide an explanation of mind.
Up to Lamarck, mind was the explanation of the biological world. But, hey presto, the question now arose: Is the biological world the explanation of mind? That which was the explanation now became that which was to be explained."
"Lamarck was the first to propose a coherent theory of evolution, according to which all living beings have evolved from earlier, simpler forms under the pressure of their environment. Although the details of the Lamarckian theory had to be abandoned later on, it was nevertheless the important first step."
Charles Darwin (1809-1882)
"Several decades later Charles Darwin presented an overwhelming
mass of evidence in favor of biological evolution, establishing
the phenomena for scientists beyond any doubt. He also proposed
[the mechanisms of] natural selection, which were to remain the
cornerstones of modern evolutionary thought...
The discovery of evolution in biology forced scientists to abandon
the Cartesian conception of the world as a machine that had emerged
fully constructed from the hands of its Creator. Instead, the
universe had to be pictured as an evolving and every changing
system in which complete structures developed from simpler forms."
"Darwin also made specific contributions to human psychology, tracing the origins of emotional responses and facial expressions from prehuman species, in The Expression of the Emotions in Man and Animals."
Evolutionary theory has had a strong influence on psychology.
If humans evolved from the same evolutionary tree as other animals
than much of human behavior would operate on the same principles
as animal behavior, and thus it might be relevant for psychologists
to study animals (see 'behaviorism'). In addition, if evolution
selects behavior through natural selection than human behavior
can also be studied through the perspective of how it has served
our species (see 'functionalism').