Tools have changed our genes for millions of years. Paleo-people were not possible without them. Artificial aids preceded and enabled our bigger brains. The slings and arrows of our evolutionary fortune have not been entirely random. We have long intelligently designed factors in our own evolution.

Chipped-stone hand axes testify that our ancestors used tools over two million years ago. And tool marks overlaid on animal teeth marks mean axes were likely used to extract marrow from the skeletons of dead megafauna. Derek Bickerton says that new tool-enabled nutrition started a trend toward a threefold increase in our brain size. Stone tool marks under animal bite marks show that by two million years ago cooperative hunting had begun. But tool development was slow. The symmetrical pear shape of hand axes remained unchanged “for more than a million years,” and we have no evidence of effective spears until 500,000 years ago, nor of spear tips or multi-part arrows until 90,000 years ago.

Tools and weapons enabled us to “evolve biological deficits,” they substituted for “massive teeth, claws and muscles," writes Timothy Taylor. Our ancestors "de-evolved” to become weaker, releasing resources for energy-hungry bigger brains (which now make up 2% of our body mass, but consume 20% of our energy). Other species use tools—for example chimpanzees dig with sticks—but they can manage without them. Not so for our ancestors. For paleo-people no tools meant no survival.

“Survival of the fittest” is evolutionarily useless unless it leads to reproduction, and our ancestors had to raise utterly helpless, long dependent offspring. A prehistoric artificial aid, still widely used today, helped with that challenge. Dean Falk says “The fossil record suggests that our ancestors had adopted a fully terrestrial way of life that most likely entailed the use of baby slings by...1.6 million years ago.” For mobile furless bipeds, carrying infants was arduous, consuming as much energy as lactation (about 500 calories a day). Using a baby sling takes 16% less energy than hip-carrying an infant.

Darwin understood the key role of tools in our evolution: “If some one man in a tribe, more sagacious than the others, invented a new snare or weapon...the plainest self-interest, without the assistance of much reasoning power, would prompt the other members to imitate him; and all would thus profit.”

Our tools created strong selective pressures favoring the mental and manual skills required to make and use them. An unavoidable part of our environment for millions of years, artificial aids that we intelligently designed influenced our own evolution. Marshall McLuhan’s observation that "we shape our tools, and then our tools shape us," is deeply biologically true.

Illustration by Julia Suits, The New Yorker Cartoonist & author of The Extraordinary Catalog of Peculiar Inventions.

Previously in this series:

It Is in Our Nature to Be Self-Deficient

Inheriting Second Natures

Our Ruly Nature

It Is in Our Nature to Need Stories