So, on the 24 November 1859, Charles Darwin's On the Origin of Species was published. So happy 150th birthday, a piece of scientific literature I have actually never read. So, I thought I could take a moment to look at the influence this book has had on the biology as a science.

So, to begin with, Darwin did not invent the term "evolution". As a concept, it has existed since the ancient Creek philosophers. Aristotle had this idea how the first animals were simple and some of them evolved further and further, becoming more intelligent and complex. And of course human were the most evolved creatures on the planet. (The idea many people who don't understand evolution seem to hold even today)

During the middle ages the Christian Church took hold, assimilating the writings of the Creek philosophers and interpreting them in the light of the bible. During this time life was thought to just appear out of nothing ever once in a while, and just transform randomly. At the time it was thought that when maggots and flies appear in corpses and spoiled food, it's actually the corpse or food turning into the flies. This theory was ultimately dis-proven by Louis Pasteur, and later replaced by the Germ theory.

In any case, because of the protestant reformation, as well as the fact that the bible was made available to the common man, and not only selected few, the idea of biblical literalism started to gain popularity. According to it the story of creation in the bible was to be interpreted literally, and that all the lifeforms were created by god and all the species were unchanging.

To what extent they were unchanging were of course not clear, and some scientists suggested that maybe some similar animals, such as the big cats, all shared an ancestor. Some went even further, and suggested that all living things(including humans) might be related. After all, just by looking at the limbs of all the mammals you can see the design is basically the same.
Jean-Baptiste Lamarck was one of the first to introduce a theory of how this populations changing over time would work. His idea was that acquired characteristics could be inherited by the offspring. This idea is usually illustrated with giraffes; the ancestors of giraffes had short necks. They would stretch their necks, trying to reach higher, and so every generation would have longer necks.

Also, remember that the people of that time had no idea how genetics worked. And neither did Darwin, actually. So, let's take a look at Darwin, and his contributions for the biology. Actually, let's just look at the Origin, since I don't feel like going through all of his work. He might be remembered for his evolutionary theory, but that wasn't his whole work.

The idea he came up with was the natural selection. As the ideas go, it's actually pretty simple; individuals in a population vary within some limits; the ones that are successful get laid and have offspring, passing on their qualities to the next generation. To use the giraffes as an example again; The ancestors of the giraffes had shorter necks; however, some of them had a bit longer neck than the others; this gave them some advantage; they could reach higher, and got food the shorter ones could not. Natural selection favored the long-necked ones, and they got more offspring than the others, leading for the necks to grow in length.

Darwin had a lot of data to support his theory, from the Beagle expedition in the 1830s and his subsequent findings from research, correspondence, and experimentation. He had no idea how the characteristic were passed along to the next generation, after all he had no idea about genetics, or mutations. However, his theory was widely accepted by the scientific community.

Mendel's experiments with beans were not widely known, and even he thought they only applied to some plants. His research was re-discover in the 1900's and finally became the basis of the classical genetics.

After Darwin, there were several competing theories to explain the evolution. Mainly because many scientists felt that while evolution was a fact, Darwin's theory about the natural selection was not enough to explain it all. However, when genetics matured as a field, and the laws of inheritance and mutations were being discovered, it became clear that Darwin's theory was the best model. The modern evolutionary theory combines Darwin's ideas about the variation and natural selection with what we now know about the genetics.

As for why I haven't ever read the Origin, well it was published 150 years ago. I tend to try to learn my science from a bit more modern publications. It has it's place in the history of biology, and founding the field of evolutionary biology, but a lot of it is out of date, and if you don't know much of biology, and are thinking about starting to study it, go read some modern literature. The science has progressed during these 150 years.