In the history of marketing, there’s a classic tale that centers on the humble cake mix. During the nineteen-fifties, there were differences of opinion over how “instant” powdered cake mixes should be, and, in particular, over whether adding an egg ought to be part of the process. The first cake mixes, invented in the nineteen-thirties, merely required water, and some people argued that this approach, the easiest, was best. But others thought bakers would want to do more. Urged on by marketing psychologists, Betty Crocker herself began to instruct housewives to “add water, and two of your own fresh eggs.”

The cake-mix debate may be dated, but its central question remains: Just how demanding do we want our technologies to be? It is a question faced by the designers of nearly every tool, from tablet computers to kitchen appliances. A dominant if often unexamined logic favors making everything as easy as possible. Innovators like Alan Kay and Steve Jobs are celebrated for making previously daunting technologies usable by anyone. It may be hard to argue with easy, yet, as the add-an-egg saga suggests, there’s something deeper going on here.

The choice between demanding and easy technologies may be crucial to what we have called technological evolution. We are, as I argued in my most recent piece in this series, self-evolving. We make ourselves into what we, as a species, will become, mainly through our choices as consumers. If you accept these premises, our choice of technological tools becomes all-important; by the logic of biological atrophy, our unused skills and capacities tend to melt away, like the tail of an ape. It may sound overly dramatic, but the use of demanding technologies may actually be important to the future of the human race.

Just what is a demanding technology? Three elements are defining: it is technology that takes time to master, whose usage is highly occupying, and whose operation includes some real risk of failure. By this measure, a piano is a demanding technology, as is a frying pan, a programming language, or a paintbrush. So-called convenience technologies, in contrast—like instant mashed potatoes or automatic transmissions—usually require little concentrated effort and yield predictable results.

There is much to be said for the convenience technologies that have remade human society over the past century. They often open up life’s pleasures to a wider range of people (downhill skiing, for example, can be exhausting without lifts). They also distribute technological power more widely: consider that, nowadays, you don’t need special skills to take pretty good photos, or to capture a video of police brutality. Nor should we neglect that promise first made to all Americans in the nineteen-thirties: freedom from a life of drudgery to focus on what we really care about. Life is hard enough; do we need to be churning our own butter? Convenience technologies promised more space in our lives for other things, like thought, reflection, and leisure.

That, at least, is the idea. But, even on its own terms, convenience technology has failed us. Take that promise of liberation from overwork. In 1964, Life magazine, in an article about “Too Much Leisure,” asserted that “there will certainly be a sharp decline in the average work week” and that “some prophets of what automation is doing to our economy think we are on the verge of a 30-hour week; others as low as 25 or 20.” Obviously, we blew it. Our technologies may have made us prosthetic gods, yet they have somehow failed to deliver on the central promise of free time. The problem is that, as every individual task becomes easier, we demand much more of both ourselves and others. Instead of fewer difficult tasks (writing several long letters) we are left with a larger volume of small tasks (writing hundreds of e-mails). We have become plagued by a tyranny of tiny tasks, individually simple but collectively oppressive. And, when every task in life is easy, there remains just one profession left: multitasking.

The risks of biological atrophy are even more important. Convenience technologies supposedly free us to focus on what matters, but sometimes the part that matters is what gets eliminated. Everyone knows that it is easier to drive to the top of a mountain than to hike; the views may be the same, but the feeling never is. By the same logic, we may evolve into creatures that can do more but find that what we do has somehow been robbed of the satisfaction we hoped it might contain.

The project of self-evolution demands an understanding of humanity’s relationship with tools, which is mysterious and defining. Some scientists, like the archaeologist Timothy Taylor, believe that our biological evolution was shaped by the tools our ancestors chose eons ago. Anecdotally, when people describe what matters to them, second only to human relationships is usually the mastery of some demanding tool. Playing the guitar, fishing, golfing, rock-climbing, sculpting, and painting all demand mastery of stubborn tools that often fail to do what we want. Perhaps the key to these and other demanding technologies is that they constantly require new learning. The brain is stimulated and forced to change. Conversely, when things are too easy, as a species we may become like unchallenged schoolchildren, sullen and perpetually dissatisfied.

I don’t mean to insist that everything need be done the hard way, or that we somehow need to suffer like our ancestors to achieve redemption. It isn’t somehow wrong to use a microwave rather than a wood fire to reheat leftovers. But we must take seriously our biological need to be challenged, or face the danger of evolving into creatures whose lives are more productive but also less satisfying.

There have always been groups, often outcasts, who have insisted on adhering to harder ways of doing some things. Compared to Camrys, motorcycles are unreliable, painful, and dangerous, yet some people cannot leave them alone. It may seem crazy to use command-line or plain-text editing software in an age of advanced user interfaces, but some people still do. In our times, D.I.Y. enthusiasts, hackers, and members of the maker movement are some of the people who intuitively understand the importance of demanding tools, without rejecting the idea that technology can improve the human condition. Derided for lacking a “political strategy,” they nonetheless realize that there are far more important agendas than the merely political. Whether they know it or not, they are trying to work out the future of what it means to be human, and, along the way, trying to find out how to make that existence worthwhile.

Tim Wu is a professor at Columbia Law School and the author of “The Master Switch.” This is Part III in a series on technological evolution. Part I was “If A Time Traveller Saw A Smartphone.” Part II was “As Technology Gets Better, Will Society Get Worse?”

Illustration by Hannah K. Lee.