The diagrams below show two cutting tools made from stone. They are from an early period and a later period of human history. The tools were made by breaking off small pieces of stone.

The illustration details the evolution of stone cutting

tools

used by prehistoric men in the Stone Age. As is evident from the diagram, the key difference between the cutting

tools

in the two periods is the size, with the latter version becoming noticeably larger. Tool B

also

appears more refined than tool A in terms of shape and sharpness. 1.4 million years ago, the cutting tool was thin, measured 7-8 centimeters in length, and did not display much craftsmanship. They were

also

rather uneven in appearance: the front and the back were shaped differently, and the surface appears to have been quite rough. 600,000 years later, it is obvious that the cutting

tools

used by man in the Stone Age had become significantly more advanced. First of all, they were larger, measuring 10-11 centimeters in length, and had a more definite tear-drop shape: fat at the base and tapering aggressively toward a sharp tip

whereas

the prior versions tended to be obtuse.

Second,

both front and back sides were ground more evenly and smoothly. It would

also

seem that man had learnt to sharpen the sides of their cutting

tools

as well.