In 1859, Louis Pasteur was just beginning a series of experiments disproving the theory of spontaneous generation.

In 1859, diseases were thought to be caused by miasma — bad air — despite John Snow’s work on the 1854 cholera outbreak in London.

In 1859, Gustav Kirchhoff formulated the law of black-body radiation.

In 1859, scientists believed that the atom was as small as particles got.

In 1859, James Clerk Maxwell was researching electricity and magnetism. Three years later he would make the astounding claim that light was electromagnetic in nature.

In 1859, scientists believed that light moved through an invisible medium called the luminiferouos aether.

In 1859, Gregor Mendel was in the middle of his experiments with pea plants that would lead to his laws of inheritance.

In 1859, the first recognized fossil of an ancient human variant had only been discovered for three years.

In 1859, after more than twenty years of gathering evidence and refining his theories, Charles Darwin published On the Origin of Species by Means of Natural Selection.

Darwin did not invent the idea of evolution. The debate over whether species were immutable or not had been going on for a long time. His own grandfather had theorized that species changed over time. But On the Origin of Species was a masterpiece of lucid, logical thought coupled with exhaustive, documented evidence.

Darwin was not completely correct. He knew nothing of genetics, and could only guess at how traits were passed from generation to generation. Yet the core of his theory was sound, and his theory of natural selection, which took decades to be accepted, is the bedrock on which much has been built.

Good scientific work is often subsumed into newer, more complete work. We learn more about how the world works, and older theories are superceded by newer ones. Only a handful of physical theories not only fundamentally changed how we viewed the world but also remain strikingly relevant today. Newton’s work on mechanics. Maxwell’s four equations. Mendel’s work on inheritance. To those add Darwin’s work on natural selection.

Happy 200th birthday, Charles Robert Darwin.