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Play, Not Necessity, Is the Mother of Invention

A story of how humans invented the wheel and macaques invented the hammer.

Key points

  • Play is an important part of early development that leads to learning and creativity.
  • Non-human animals can also develop tools and objects through play.
  • One example is how macaque monkeys playing with stones learned how to use them to crack shells and get food.
Source: The National Gallery of Art/Rawpixel/Public Domain
Ox Cart (1935–1942) by Wilbur M Rice.
Source: The National Gallery of Art/Rawpixel/Public Domain

Necessity is the mother of invention,” according to the well-known English proverb. But is it really? I suggest here a revision, which I think has more truth: “Play is the mother of invention; necessity is the mother of engineering.”

Play opens the mind to original ideas and creations; necessity takes some of those creations and refines them for practical ends. Play takes us into the realm of imagination. Necessity keeps us focused on the here and now, the familiar, to solve immediate problems.

Who Invented the Wheel and Axle?

Here’s an example. The wheel—or, more accurately, the wheel-axle combination that makes it possible to build a cart—is often regarded as the greatest technological invention in human history. It revolutionized the way people lived. The cart, especially if you hitched an ox to it, made it possible to haul heavy loads of lumber or agricultural produce or anything over land far more efficiently than before. People no longer had to live next to rivers if they needed to transport things. Once the cart was developed, it went viral, as we would say today. Soon (well, within a couple of centuries), there were carts everywhere.

The earliest functioning wheels and axle in the archaeological record, however, were not under a cart but under a small ceramic coyote, a child’s toy, found with the remains of a child buried about 6,000 years ago (Cassidy, 2020). It was most likely made by some playful potter who thought it would be fun and provide entertainment for their child to make a toy animal that could be pulled easily with a string without falling over. Similar findings were made, dating just a bit later, in various places in northern Europe.

It was not until several centuries later that skilled European craftsmen took the wheels and axle idea to build functioning carts. The cart was an amazing feat of engineering for its time. The wheels and axles had to be perfectly round to minimize friction and the whole thing stout enough to bear heavy weights. But the engineering would not have been possible had not the model of a wheel and axle already been available in the craftsman’s world, in the simpler, more crude, miniature, easier-to-make form of children’s toys.

It would be interesting, I think, to examine the whole history of technology, from the wheel to the modern desktop computer, to see how the original insight that led to that creation arose. I haven’t yet done that research, but I bet that, in many cases, the insights arose in play. People just fooling around for fun or to create a toy of some sort came up with a truly new idea, which later turned out to have practical applications when engineers or technicians got their hands on it and made appropriate refinements. But now I’ll turn to an example from the non-human animal world.

How Did Macaque Monkeys Discover That Stones Can Crack Shells?

Technological invention is rare in non-human animals, but wherever it has been documented, the young of the species appear to gain the first insight through play. Here’s my favorite example, which comes from extensive observations of macaque monkeys in Japan.

Beginning in the 1970s, juvenile macaques in some groups were observed playing with stones, a previously unobserved behavior (Huffman, Nahallage, & Leca, 2008). They would pick them up, sometimes cuddle them like babies, sometimes throw them, and—most significantly for our story—sometimes smash one stone against another, apparently enjoying the sound. To the degree that the observers could tell, this was all pure play; it seemed to serve no purpose other than enjoyment.

At first, only juveniles played this way. Adults neither invented such behaviors nor imitated the young. However, younger juveniles imitated older ones in stone play, and stone players continued to play with stones when they themselves became adults. So, in later observations, adults as well as juveniles could be seen playing with stones, and new young macaques picked up the behaviors from their elders. So, stone play became a cultural tradition in some macaque groups, a characteristic of the whole colony, transmitted from generation to generation.

Then, some years later, researchers found a group of coastal living macaques that not only played with stones but also used them to crack open shellfish (Tan, 2017). The step from smashing a stone against a stone to produce a sound to smashing a stone against a clam to produce food was a relatively small one, but it had the huge consequence of turning the stone from a plaything to a tool. We don’t know just how that step occurred or whether it was a juvenile or an adult who first took it, but a category of behavior developed originally by juveniles in play provided the foundation for a valuable new way of obtaining food for these shore-living macaques. Once stones were used to crack shells, macaque engineers (to use the term loosely) modified the smashing technique for maximal effect in opening shells.

So, we have here not just an example of play providing the foundation for a tool but an example in which the play form itself was clearly initiated and carried on by juveniles. The behavior became a cultural tradition for adults only when the juvenile inventors became adults.

Further Thoughts

The macaque example illustrates a general idea, which is far truer for humans than for macaques or any other animal group. The idea is this: The juvenile phase of life is a phase of discovery and invention.

When a child comes into the world, everything is new to that child. Everything the child learns about the world is a discovery, and every skill the child develops is an innovation. Children are primed for discovery and invention. Curiosity and playfulness are the means of that priming.

As humans grow older and more experienced, they develop more fixed beliefs and set ways of doing things, and consistent with that, the drives to explore and play tend to decline. Some people (such as the scientists I described in my last post) manage to hold on to high levels of curiosity and playfulness throughout their lives, and those people may continue to develop new insights throughout their lives that add to the culture.

But the peak of inventiveness, more generally, is adolescence and young adulthood. These are people who know quite a bit about the world but recognize that there is still so much out there that they do not know and would like to know. Their degrees of playfulness and curiosity are still high (unless they have been quashed by forced schooling), and that, combined with their growing knowledge and skill, prime them for culturally new discoveries and inventions.

This post is also published on my Substack here, where you can leave comments.


Cassidy, C. (2020). Who invented the wheel? Chapter in Cassidy’s book, Who Ate the First Oyster?

Huffman, M. A., Nahallage, C. A. D., & Leca, J-B. (2008). Cultured monkeys: Social learning cast in stones. Current Directions in Psychological Science, 17, 410-414.

Tan, A. W. Y. (2017). From play to proficiency: The ontogeny of stone-tool use in coastal-foraging long-tailed macaques (Macaca fascicularis) from a comparative perception-action perspective. Journal of Comparative Psychology, 131(2), 89–114.

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