The goal of this first section is to dispell a bit of myth about Science and 'The Scientific Method'. Science has manged to attain a mythical status for itself: The purveyor of truth, the only avenue to real practical knowledge, "Scientists show that...", and for a day to day purpose perhaps it is appropriate. But from a purely philosophical point of view it is far from an accurate representation.
A naieve point of view of science has it that the Scientific method is all about observing, hypothesising, testing and proving. It is unlikley that any science is ever really done that way. A more sophisticated view was presented by Karl Popper: Hypothesis, try to falsify. Karl popper revolutionised the way the world viewed science; suddenly there was a criteria for whether something was Scientific or not. If it was falsifiable, it was scientific. All scientists were supposed to have a theory on how things worked, and they were then supposed to spend all of their time trying to prove the theory wrong so that an improved theory could be stated. This is of course too idealistic for reality. Scientists rarely set their goal as "Prove general relativity wrong" "Prove the atomic model wrong" "Prove evolution wrong". While the concept surrounding Poppers philosophy of science is logically sound, specifically, no theory can ever be proven correct but a theory can certainly be proven wrong, most scientists actually do neither in their work. Most scientists work to discover new concepts within a theory.
This is where Thomas Kuhn's theory of Scientific Revolutions comes in as a descriptive philosophy of science. Popper seemed to hit on something of a prescriptive ideal for science: Science should forever strive to prove itself wrong so that it may reliably move on whenever it is wrong. It must not cling to theories for the sake of tradition or sentimental sake. Kuhn's theory of science however much more accurately described what scientists do: They use the prevailing theory of the day (the Paradigm) to guide their actions in their research. The Paradigm (for instance Newtonian Physics, General relativity, quantum mechanics or evolution) creates a system of beliefs for the scientists and provides them with a 'Tool Kit' for how to go about studying their field. They use these beleifs so that their observations make sense, then their observations are made to fit with the paradigm, and the combination of their paradigm tool kit logic and paradigm inspired observations are intwined to make predictions and generate new research avenues.
Scientific revolution occurs when anomolies arise from the research which no amount of effort will force into the paradigm belief system. A few anomalies are allowed to exist for a while, rationalised as bad data, bad technique, specific case or simply ignored until a later time, but when numerous anomalies come to the surface it is inevitable that one or more scientists will be forced to acknowledge these anomolies. Contrary to Poppers theory of falsification the paradigm is not discarded at the first sign of trouble. With mounting anomalous results some (certainly not all) scientists will start to question the paradigm, but ultimately will be ignored because a paradigm is required for science to continue. Without a paradigm, how will the data be interpretted? It isn't until someone manages to put the peices of the puzzle together to formulate a new hypothesis which actually manages to cover all of the previous data as well as the new anomolous data in one fancy new theory that some people will start to consider discarding the old paradigm. Even then many scientists will cling to all they know and not accept the new paradigm.
With this quick introduction to the Philosophy of Science it is clear to see that Evolutionary Theory is the paradigm under which Biology currently operates. It is used as a toolbox to make predictions about molecular biology, morphology of organisms, paleantology, even medicine. Evolution came to be the accepted scientific paradigm more than 50 years after Origin of The Species was written after the particulate inheritence of genetic material was rediscovered. Until that was rediscovered it was assumed that all offspring blended the characteristics of their parents and so would reduce diversity rather than increase it as predicted by Darwins theory. Evolution replaced the previous paradigm: Creationism. until the Evolution was set up as the Paradigm, no theory adequately described life on earth sufficiently well at all (Lamarkianism was a contender, but never fully accepted) and in general people assumed "God made it" in whatever form they wanted to believe God did it.
As a scientific theory, creationism is a non-paradigm, it makes no active tool kit and no method of interpretting the data. Everything you see can be explained with "And thats how God wants it". Everything is equally perfect in its own way, and everything has its perfect purpose. The theory is functionally useless from a scientific point of view, and this can be argued on both counts of Kuhnian philosophy as well as Poopperian philosophy. "God made it" is impossible to falsify. Evolutionary theory, from a scientific point of view was far superior to its predessesor.
Clearly no year can ever be placed on the implementation of a paradigm, but a time frame may be indicated from when it started to be taught in educational institutions. Evolution really started to be accepted inthe early 1900's. Since then, the increase in biological knowledge has been staggering. From accepting that genetic inheritence was particulate (that is there is a peice of genetic material which is inherited in its entirety that determines a trait: a gene for blue eyes, a gene for black hair etc) to discovering the double helix structure of DNA and showing that it was the genetic material, to then mapping the entire genomes of over 180 organisms in the last 10 years!!! For a paradigm to encounter that amount of NEW, BRAND NEW information integration and stay as the only contended paradigm is a true indication of the strength of the theory of evolution.
Also interesting to find out: How many paradigms ahve come into phsyics since evolution was proposed? General relativity, special relativity, quantum mechanics... and physics has not advanced nearly as fast or as far as Biology.
Synopsis of Kuhns Scientific Revolutions
Wikipedia entry on Kuhn
Wikipedia entry on Popper