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

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

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

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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

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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

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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

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the prior versions tended to be obtuse.

Second,

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

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

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as well.