If you trace back along the path of human evolution (the homo genus to be more specific) there’s a period where our species started to undergo rapid changes. The actual time varies wildly depending on the sources you read but the cause isn’t: it was when we learnt to control fire. Fire enabled our ancestors to do many things that simply weren’t possible before like cooking food (which provides easier access to calories and nutrition), doing activities at night as well as during the day and even protecting themselves from animals and insects. Indeed the species were are today, one that is well adapted for cooked food, is because of our beginnings as masters of fire.
I’m also somewhat fascinated with the creation of fire, possibly from a purely primal level, but also because there’s numerous different ways to do it and each of them exploit a physical principle. One of the most interesting ones I saw recently was someone using a hammer to light a cigarette:
At the highest level what is being done here is that kinetic energy, from the hammer falling on the piece of metal, is being translated into heat. This is accomplished by the bending and warping of the metal that occurs when its struck by the hammer which breaks down the bonds between the metal atoms causing them to release heat. The second part of the trick here is that they then utilize a highly flammable tinder, I.E. the cigarette, which has a flash point below that of the temperature of the metal. Drawing air over it provides more oxygen and with that you have all the ingredients you need for fire.
Of course it’s not the most practical way of creating fire given the materials required to do it. You’re much better off with a flint and steel as they produce sparks with temperatures that far exceed that of hammered metal. That is of course if you don’t have any matches, cigarette lighters or any number of modern fire making devices handy but for pure reliability you really can’t go past a good old fashioned piece of flint and steel.