The diagram illustrates the development of the cutting tool from two different time periods within the Stone Age.
Although the overall size and shape of the two cutting tools are very similar, the cutting tool from the latter time period shows some distinct improvements.
Tool A is a depiction of a Stone Age cutting tool used approximately 1.4 million years ago, while tool B is from a later part of the Stone Age approximately 0.8 million years ago. Both cutting tools are similar in shape and size, being roughly 10cm in length. However, tool A looks to be quite a crude implement, while tool B appears to have been refined into a more effective cutting device.
From the front and rear view, tool B appears to be much wider than tool A and has a rounder body shape. The cutting edges also appear to be more distinct and symmetrical. The side view shows a distinct difference in the thickness of the two tools, with tool B significantly slimmer than tool A.