"Homo Deus" by Yuval Noah Harari: Summary and Review

Sapiens ended with a question: what will humans become? Homo Deus, published in English in 2016, is Yuval Noah Harari’s long answer. Its title is Latin for “the human god”. Harari argues that the old enemies of humankind are mostly defeated. Our next goals, he says, are to live forever, to be happy all the time and to gain the powers of gods. In trying, we may make ourselves unnecessary. This review explains the book’s main ideas and is honest about where experts think it goes wrong.

What kind of book this is

Homo Deus is a book about the future written by a historian. Harari does not claim to predict what will happen. In his words, the scenarios in the book are “possibilities rather than prophecies”. His aim is to show how today’s beliefs came about, so that we can see that they might change.

The book has three parts after an opening chapter. The first part asks how humans came to rule the world. The second part asks how humans gave meaning to the world. The third part asks how humans might lose control of it. If you have read Sapiens, the first part will feel familiar. Our review of it is “Sapiens” by Yuval Noah Harari: Summary and Review.

Famine, plague and war have become manageable problems

Harari opens with a claim about progress. For thousands of years, famine, plague and war were the main dangers in human life. People saw them as forces of nature or as the will of God. Harari argues that in the last century they became problems that humans can manage.

He sums this up in a famous sentence, quoted in full among the key quotes below. For the first time in history, he writes, more people die from eating too much than from eating too little. More people die of old age than of infectious diseases. More people kill themselves than are killed by soldiers, terrorists and criminals together. Harari does not say these problems are gone. He says that when they happen now, they are usually caused by human failure, not by fate.

The new human agenda is immortality, happiness and divinity

If survival is mostly solved, what comes next? Harari’s answer is the new human agenda. It has three goals.

1. Immortality. Death becomes a technical problem. Rich people and companies already invest in research to slow aging.
2. Happiness. Harari argues that happiness is a matter of brain chemistry. So people will try to control it directly, with drugs and other technologies.
3. Divinity. Humans will try to upgrade their bodies and minds with biotechnology, computers and genetic engineering. In Harari’s sense, a god is a being with powers far beyond our own.

Harari adds a twist about his own work. Predictions about history are not like predictions about the weather. When people hear a prediction, they can change their behavior. So the more people know history, the less it repeats. He calls this the paradox of historical knowledge.

Humans rule the world through shared stories

The first part of the book repeats the main claim of Sapiens in a new form. Humans dominate other animals because they can cooperate in very large and flexible groups. They do this through shared beliefs in things like money, gods, nations and companies. Harari calls these intersubjective realities. They exist because many people believe in them at the same time, not because they are physical objects.

Harari also asks whether humans have something animals lack, such as a soul. He argues that science has found no evidence for one. He then describes humans and other animals as algorithms, methodical sets of steps that turn inputs into decisions. This idea becomes very important later in the book.

Modern people traded meaning for power

In the second part, Harari describes what he calls the modern covenant, a kind of deal at the heart of modern life. Older societies believed that the world had a plan, written by God or by nature. That plan gave life meaning, but it also limited what people could do.

Modern societies gave up the idea of a cosmic plan. In return, they gained power. Science, industry and economic growth let humans change the world as they wished. But a world without a built-in plan seems to have no built-in meaning. Harari argues that modern people solved this problem with a new belief.

Humanism made human feelings the source of meaning

That belief is humanism. Harari uses the word for the idea that meaning comes from human experience. In a humanist world, voters decide what is right in politics, customers decide what is good in business, and your own feelings decide what is beautiful in art.

Harari treats humanism as a religion, in the sense of a belief system that tells people what is valuable. He describes three branches that fought each other in the 20th century.

• Liberal humanism trusts each individual’s feelings and choices.
• Socialist humanism trusts the feelings of people as a group, especially the poor.
• Evolutionary humanism sees conflict and natural selection as the way humanity improves. Harari links it to the Nazis.

Liberal humanism won, Harari argues. Most people today live with its values, even if they do not use the word.

Science says there is no free self, and computers may know you better

The third part is the core of the book. Harari argues that the life sciences undermine liberal humanism. If organisms are algorithms, then choices are the results of biochemical processes. There is no free self that stands outside those processes and decides.

He uses research by the psychologist Daniel Kahneman to make this concrete. Kahneman distinguished an experiencing self, which lives through each moment, from a remembering self, which later tells the story of what happened. Harari calls the second one the narrating self. The two often disagree. Which one is the real you? Kahneman’s research is explained in “Thinking, Fast and Slow” by Daniel Kahneman: Summary and Review.

Now add computers. If an outside algorithm has enough data about your body and behavior, it may predict your wishes better than you can. Harari’s examples include medical tests that read genetic risks and online services that track what people click. Once that happens, it no longer makes sense to trust only your feelings. You would ask the algorithm instead.

This idea is useful even if you doubt Harari’s predictions. Think of a music app that chooses your next song, or a map app that chooses your route. Each time, you let a system decide because it has more data than you. Harari asks you to notice these moments. Which decisions are you happy to hand over, and which ones should stay yours? The question gets harder as the systems get better.

Intelligence is separating from consciousness

Harari calls the next step the great decoupling. For most of history, only conscious beings could do intelligent work. Now computers without any feelings can drive cars, read X-rays and trade stocks. Intelligence is separating from consciousness.

This has an economic result. In the 20th century, states needed masses of people as workers and soldiers. If machines can do that work better, many people may lose their economic and military value. Harari calls them the useless class. The phrase is harsh on purpose. He does not mean that these people lack worth as humans. He means that the economy and the state might no longer need them, and might stop caring about them.

He also warns about inequality. Upgrades to the body and mind will probably be expensive at first. A small elite might become biologically different from everyone else. Harari treats this as a real risk.

Dataism could become the next religion

The last chapter describes a new belief system that Harari calls dataism. Dataism sees the universe as a flow of data. It judges the value of anything by how much it adds to data processing. Humans are then valuable as parts of a huge data processing system, not because of their feelings.

Harari gives dataism a simple rule of life. Whatever you experience, record it, upload it and share it. A humanist goes for a walk to feel something. A dataist also posts the photos, because an experience that nobody shares adds nothing to the flow of data. Harari suggests that many people already live a little like this without calling it a belief.

Harari does not say dataism is true. He says it is spreading, especially among engineers and in the technology industry. He then ends with three questions, not answers. The first is quoted among the key quotes below: are organisms really just algorithms? The second asks whether intelligence or consciousness is more valuable. The third asks what will happen when unconscious but very intelligent algorithms know us better than we know ourselves.

How it differs from other books on the future

Homo Deus belongs to a group of books about technology and human values. Three neighbors show what is special about it.

• Sapiens is its foundation. Homo Deus uses the same idea of shared stories, but points it at the future.
• Nick Bostrom’s Superintelligence is a philosopher’s careful analysis of the risks of advanced artificial intelligence. It is narrower and more technical. Harari is less interested in machines that turn against us. He is more interested in machines that make our values obsolete.
• Shoshana Zuboff’s The Age of Surveillance Capitalism studies how real technology companies collect and sell data about people. It is more grounded in evidence about the present.

What Harari adds is the link between history and belief. He shows that “trust your feelings” is not a law of nature. It is a belief that appeared at a certain time. Whatever you think of his predictions, this point is useful.

What critics say Harari gets wrong

The book has four weaknesses, and some of them are serious.

The first is biology. The historian Ian Hesketh, writing in the Sydney Review of Books, points out that Harari presents the claim that organisms are algorithms as the view of the life sciences. In fact, it is a contested interpretation, and Harari cites almost no one for it. The whole argument of the third part depends on this claim.

The second is pandemics. Harari argued that natural epidemics were largely under control. The scientist Darshana Narayanan notes that COVID-19 showed this view to be badly wrong. Narayanan also rejects his claim that body sensors could reliably read emotions, because emotions cannot be read from physical signals alone.

The third is religion. Hesketh calls the book’s story of declining religion too simple, because religious belief is growing in many parts of the world. Narayanan adds that the footnote behind Harari’s claim that dataism has won over scientists cites mostly non-scientists.

The fourth is tone. Harari writes about a future of useless people and data gods with great calm. Some readers find this refreshing. Others find that it makes a speculative future sound more certain than it is.

Which format to choose

The book is long but easy to read, and the audiobook works well. Read Sapiens first, because Homo Deus assumes its main idea. Harari later returned to these themes in 21 Lessons for the 21st Century and Nexus, his book about information networks and artificial intelligence. If you want only one book about the future of humans and technology, Homo Deus is the most thought-provoking of Harari’s books. It is not the most reliable.