Ever wondered why there's so many kinds of life in the world? Evolution is the reason. In the field of biology, none is more the king than evolutionary biology, for it is the field on which all biological sciences depend.
Evolution is not a recent idea. If you ask anyone who invented the concept of evolution, they'd probably tell you Charles Darwin invented it, roughly a century and a half ago, after sailing around the world on the Beagle, and returned to write a momentous book known as On The Origin of Species. This hypothetical person would, of course, be correct in telling you that Darwin did develop the idea of evolution as he sailed around the world and did write a momentous book of that name.
They're still wrong, though.
Evolution was not a new concept even in Darwin's time. It goes back at least 2600 years to the early Greek philosophers and is recorded in the writings of one very famous one that you've likely never heard of; Anaximander.
Of course, Anaximander believed that animals originally grew in trees, then burst out of the trees, at which point other animals growing inside them then burst out of them and so on. That's how he explained the fossil record.
Evolution, according to Anaximander
The guy sounds fairly broken in the head by our standards, but this was 2600 years ago in Greece, when buggering little boys was still fashionable and xenomorphs apparently roamed the Earth, so who are we to judge?
What is it with bald guys with big beards and Evolution?
What Darwin gave the world was not Evolution but Natural Selection. Everyone and their uncle had an idea of how evolution occurred in Darwin's day, with one of the most famous examples being Lamarck, who claimed that characteristics gained in life were passed down to future generations. If a man gained big muscles in life, he would pass on big muscles to his kids.
Darwin was different. He suggested that, instead, it was heritable characteristics being "selected" by nature that made things work. This may not seem so mind-blowing to us now but, at the time, this was such a powerful idea that it could be compared to figuring out calculus while other people are believing that the number four has super-powers.
The idea explained not only why life exists in such abundance and so many different forms but also how it came to be so. It also told us that things were continuing to change and led to a profound realization that the Earth today was not a finished work but constantly in a state of change and flux.
When you consider that Darwin figured this all out without genetic evidence or even knowing how animals properly passed on their genetic information, or even with half the evidence from the fossil record that we have today, you realize that this man had not only a mind of incredible sharpness but also balls of steel to suggest any of this.
In a word? Medicine.
These little dots want to kill you!
That is Streptococcus Pyogenes. It is just one of many, many bacterium out there developing a resistance to antibiotics. You know antibiotics, right? Those little things that mean that people all over the world don't need to worry about dropping dead from a small scrape? Well, it turns out that bacterium, like all things, evolve with time. Every time someone misuses antibiotics, there's a chance some of these little buggers will develop a defense to the antibiotic used and, in turn, reproduce and make more of themselves. This, in turn, makes antibiotics useless. Without knowledge of evolution, we'd just blindly waste one of the best advances in medicine in human history.
Even discounting all the amazing things it's contributed to worldviews, understanding of history and philosophy, evolution and evolutionary biology are essential parts of the medical field and, without it, we're sort of screwed.