It is commonly accepted that when Charles Darwin published On the Origin of Species in 1859, (1) he did for humankind what Copernicus did for the earth when the astronomer published De Revolutionibus Orbium Coelestium (On the Revolutions of the Celestial Spheres) in 1543 (2).
Where Copernicus made it clear that our planet was not the center of the universe and, indeed, that the earth revolved around the sun, Darwin articulated a vision that showed humans to be a part of nature rather than above it.
In both cases, we lost what some saw as a privileged status. It was this repositioning that encouraged many opponents, both within the Church and beyond its walls, to attack the ideas promoted by these two great thinkers.
Darwin consolidated biology
But Darwin, by explaining the role of natural selection in evolution, did something even more important than defining humans as a part of nature and, accordingly, taking away our privileged status.
The scientific genius--born 200 years ago (birth Feb. 12, 1809; death: April 19, 1882)--created the central unifying principle of biology: the construct through which biology became an integrated science rather than a random collection of facts and ideas.
Natural selection, both as outlined by Darwin and as understood today, is simple and noncontroversial. It means that those organisms best able to acquire limited resources and convert them to offspring will leave the most descendents and the genes controlling their behavior will increase in frequency.
When the scientist and philosopher Thomas Huxley first heard about natural selection, he reportedly said, "How extremely stupid not to have thought of that!"
No wonder Huxley became known as Darwin's Bulldog for his impassioned defense of Darwin's ideas.
The evolution of evolution took a winding path
What is essential to remember, however, is that genes had not yet been discovered when Darwin first proposed the concept of natural selection. So it was not at all clear what was being passed along from successful parent to offspring in response to interactions with the environment. Nonetheless, Darwin's insightful reasoning and the wealth of data he presented made for a compelling argument that some hereditary factor was being passed along.
Today, natural selection is regularly measured in both the field and the laboratory by assessing the frequency of alternative forms of genes (alleles). In fact, as important as natural selection is, today we realize that it is but one of a number of evolutionary mechanisms biologists measure and understand. Also of critical importance are mutation, migration, nonrandom mating and the effects of population size. Again, the impact of all of these factors is regularly measured in both the field and the laboratory.
Evolution took on much of its modern shape in the first half of the 20th century when it became clear that all of these factors played a role in shaping the diversity of life on Earth. The term accepted for this robust, integrated vision of evolution was the "modern evolutionary synthesis" or neo-Darwinian theory, first articulated by Julian Huxley in his 1942 book entitled Evolution: The Modern Synthesis (3). Through this lens, evolution is defined incredibly simply as a change in allele frequencies in a population over time.
Although there is nothing controversial about this idea, it is a very powerful concept that allows scientists to explain and predict a great deal. In his classic article entitled "Nothing in Biology Makes Sense Except in the Light of Evolution," (4) the great population geneticist and a primary architect of the modern evolutionary synthesis, Theodosius Dobzhansky, made this point succinctly: "Seen in the light of evolution, biology is, perhaps, intellectually the most satisfying and inspiring science. Without that light it becomes a pile of sundry facts--some of them interesting or curious but making no meaningful picture as a whole. …