I have often wondered how the first knife came about and I have some of my pet theories. They may not be anywhere near the truth but they seem plausible to me. Obviously, the invention of the "knife" was a very slow progression. It almost certainly started with the realization that certain stones performed better than others at "cutting" tasks. I would guess that this discovery was made LONG before man began to actually craft edged tools and that for a period of time man just sought out rocks with certain shapes that performed better. More specifically I would theorize that the the realization of a "cutting tool" started with skinning game.
My theory goes something like this:
Early man was naked and constantly battling starvation. Food was likely berries and plants and whatever small animals and rodents he could catch with his hands. Man discovered early that the soft and squishy part on the inside tasted much better than the chewy and hairy part on the outside. I'm sure that over the centuries, plenty of prehistoric teeth were lost chewing through hide to get to the goods. At some point man began to use rocks as tools and weapons. I wold imagine that led to smashing a rock down on these small rodents to tear open the hide. Over time, man noticed that certain shaped rocks "those with narrower edges" performed better for this work and they began to seek out those shapes for this specific use. Along the way, they likely noticed that while working like this, some types of rocks would fracture in ways that would make them even narrower and more functional along the edge. You already know the rest of the story.
Now, who else has a theory?