For millions of years the only way to kill someone would be to physically beat them to death.
The first weapon was a way for a weaker person to kill a stronger person or animal. By focusing force of a punch on a smaller surface area (knife, spear, axe), by increasing the mass of the fist (club, hammer, axe) or by eliminating the need for speed (arrow).
A gun does all of those things as efficiently as possible, while only requiring the movement of a finger to use. With it a toddler can kill the strongest person or animal that ever lived.
Your question is stupid and doesn't deserve its own thread.