Richard Feynman famously presented his students with his unique (and let's admit it, hyperbolical) view of history when he said
From a long view of the history of mankind — seen from, say, ten thousand years from now — there can be little doubt that the most significant event of the 19th century will be judged as [James Clerk] Maxwell's discovery of the laws of electrodynamics. The American Civil War will pale into provincial insignificance in comparison with this important scientific event of the same decade. (The Feynman Lectures on Physics, Volume II, 1-11)
Others might acknowledge Maxwell's work but argue that the most important scientific event in the 19th was instead the codification of the laws of thermodynamics. Many people contributed to thermodynamics, including designers of steam engines, Sadi Carnot, James Joule, and Rudolf Clausius, but it was William Thomson (later known as Lord Kelvin) who first stated the first two laws of thermodynamics in the early 1850s, and who popularized the use of the word "energy" in its modern sense.
Thermodynamics and Maxwell's equations help us understand how the universe works, but 19th-century science also brought about an increased understanding of the mechanism of living things, primarily through the discovery of the process of biological evolution by means of natural selection and sexual selection as described by Charles Darwin, whose 200th birthday we celebrate today.
To quote the famous title of Theodosius Dobzhansky's 1973 essay, "Nothing in Biology Makes Sense Except in the Light of Evolution." Yet Darwin was clearly aware from the beginning of his researches that evolution had profound implications not just for biology in general, but for the origins of human beings. Evolution answered millennia-old questions like "Where did we come from?" with the revelation of a marvelous process involving the accumulation of small incremental changes tested for viability in the real world over millions of years, accepting what works, abandoning what's harmful.
We are part of this process, so evolution also tells us much about ourselves. Every other living thing is one of our distant cousins. Instead of having "dominion" over all the earth, we are yet another creeping thing that creepeth upon the earth. We came about through a blind, mechanistic, natural process, yet one that led to the development of minds capable of self reflection and wonderment, including the inquisitive, experimental, brilliant mind of Charles Darwin.
Evolution is a process more beautiful than any work of art, more awe-inspiring than any miracle, more meaningful than any theology.