DAR ES SALAAM, Jan. 31 -- OUR prehistoric human ancestors relied on deliberately modified and sharpened stone tools as early as 3.3 million years ago. The selection of rock type depended on how easily the material could be flaked to the desired shape and form.

The resulting product proved invaluable for everyday tasks. Sharp-edged rock fragments were manufactured to suit various needs, including hunting and food processing.

The Stone Age period lasted from about 3.3 million years ago until the emergence of metalworking technologies. Throughout this time, diverse tool-making traditions flourished. Among them is the Oldowan tradition, one of the earliest technological systems created by our early ancestors.

The tools are not shaped to ha...