For the past four billion years or so the only way for life on Earth to produce a sequence of DNA—a gene—was by copying a sequence it already had to hand. Sometimes the gene would be damaged or scrambled, the copying imperfect or undertaken repeatedly. That is no longer true. Now genes can be written from scratch and edited repeatedly, like text in a word processor. The earliest stages of such “synthetic biology” are already changing many industrial processes, transforming medicine and beginning to reach into the consumer world. Progress may be slow, but with the help of new tools and a big dollop of machine learning, biological manufacturing could eventually yield truly cornucopian technologies. The scale of the potential changes seems hard to imagine. But look back through history, and humanity’s relations with the living world have seen three great transformations: the exploitation of fossil fuels, the globalization of the world’s ecosystems after the European conquest of the Americas, and the domestication of crops and animals at the dawn of agriculture. All brought prosperity and progress, but with damaging side-effects. Synthetic biology promises similar transformation. To harness the promise and minimize the peril, it pays to learn the lessons of the past. Start with the most recent of these previous shifts. Fossil fuels have enabled humans to drive remarkable economic expansion in the present using biological productivity from ages past, stored away in coal and oil. But much wilderness has been lost, and carbon atoms which last saw the atmosphere hundreds of millions of years ago have strengthened the planet’s greenhouse effect to a degree that may prove catastrophic. Here, synthetic biology can do good. It is already being used to replace some products made from petrochemicals; in time it could replace some fuels, too. The second example of biological change sweeping the world is the Columbian exchange, in which the 16th century’s newly global network of trade shuffled together the creatures of the New World and the Old. Horses, cattle and cotton were introduced to the Americas; maize, potatoes, chili and tobacco to Europe, Africa and Asia. But there were also disastrous consequences. Measles, smallpox and other pathogens ran through the New World like a forest fire, claiming tens of millions of lives. The Europeans weaponized this catastrophe, conquering lands depleted and disordered by disease. Synthetic biology could create such weapons by design: pathogens designed to weaken, to incapacitate or to kill, and perhaps also to limit themselves to particular types of target. There is real cause for concern here—but not for immediate alarm. For such weaponization would, like the rest of cutting-edge synthetic biology, take highly skilled teams with significant resources. The earliest biological transformation—domestication—produced what was hitherto the biggest change in how humans lived their lives. Haphazardly, then purposefully, humans bred cereals to be more bountiful, livestock to be more docile, dogs more obedient and cats more companionable. This allowed new densities of settlement and new forms of social organization: the market, the city, the state. Humans domesticated themselves as well as their crops and animals, creating space for the drudgery of subsistence agriculture and oppressive political hierarchies. Synthetic biology will have a similar cascading effect, transforming humans’ relationships with each other and, potentially, their own biological nature. The ability to reprogram the embryo is, rightly, the site of most of today’s ethical concerns. It will not be perfect: there will certainly be unanticipated effects. But synthetic biology will be driven by the pursuit of goals, both anticipated and desired. It will challenge the human capacity for wisdom and foresight.