The evolution of human intelligence during the past three to four million years can be seen to reflect an increasingly sophisticated use of tools,¹²...beginning with simple rocks and other natural devices, and culminating non-linearly in the use of computers and robots. This process has likely been facilitated through a feedback mechanism. Anthropologist Sherwood L. Washburn believes that it wasn't only better brains that improved tools, but that using tools made better brains. He has stated that the evidence indicates that it was after humans started making tools and weapons that the real explosion in brain size occurred. The use of better tools in a wider variety of ways helped to promote a more rapid growth of the forebrain.¹³

Other occurrences also enhanced the rate of evolution of human intelligence. The freeing of hands by upright walking and the development of language contributed significantly. Richard Leakey has stated, "This behavioral complex, once initiated, fed back on itself, pushing evolution faster and faster, eventually to produce the human species.".¹⁴...He believes that the development of language is probably the latest step, and probably the most significant one, in the evolution of the human brain.¹⁵...The use of productive oral-auditory language likely began the major explosion in human evolution about 35,000-40,000 years ago at the time of Cro-Magnon man. It is about that time that clear signs of human symbolic capacities, including pictures, emerged.¹⁶

According to Leakey, the invention of agriculture about 10,000 years ago also played a very important role in the process of human evolution. He has stated that, "The invention of agriculture was without exaggeration the most significant event in the history of mankind.".¹⁷...Food supplies could now be concentrated into small areas allowing the formation of villages, towns and eventually cities.¹⁸...Farming societies allowed for population growth. This in turn allowed the more exceptional individuals--who were most likely to make new discoveries, perfect new skills and innovate the old--to perform these functions.¹⁹...Each new invention further acts to divide those individuals who can master its use from those who cannot. This tends to select reproductively in favor of those who can.²⁰

In the past several million years the strongest selection pressure in man has been for behavioral traits of increasing intellectual complexity, including comparing, analyzing, separating, and grasping relationships, as well as classifying, counting, abstracting, conceptualizing, recalling, imagining and planning.²¹...Ethologist Konrad Lorenz points out that these mental manipulations must come from environmental demands acting directly upon the large range of behaviors made possible by the increasingly complex nervous functions of our developing cerebrum.²²

Jonas Salk, one of the discoverers of the polio vaccine, has stated that humankind has moved into a new epoch where evolution favors "the survival of the wisest.".²³

As the human brain evolved, it gradually developed the attribute of foresight and the ability to use logic. As soon as there were men and women in the species who knew how to pick up a stone in advance, this gave them an obvious advantage over those who didn't. Those who can think or plan ahead have the obvious survival advantage. They can keep themselves alive when others are starving.²⁴...It is the same mechanism of natural selection which has always been operational throughout all of existence. This mechanism unquestionably favors intelligence when all else is equal.

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