The handaxe problem

Acheulean sites sometimes contain thousands of handaxes, many unused, some too large to wield. Explanations proposed include a general-purpose butchery knife, a core carried as a source of flakes, a projectile, and — more contentiously — a display of skill selected for socially, since bilateral symmetry is costly to achieve and hard to fake. The lack of change across a million years is as puzzling as the form: whatever cognitive process produced the handaxe was clearly conservative in a way ours is not.