Homo Deus: A Brief History of Tomorrow

The new human agenda

Harari opens with a claim that sounds strange at first. For thousands of years, three problems filled the human agenda: famine, plague and war. Today, he argues, humans have largely brought all three under control. They still happen, but they are no longer acts of God that nobody can stop. They are failures of policy that someone can be blamed for. In the early twenty-first century, more people die from eating too much than from hunger, more die of old age than of infectious disease, and more die by suicide than in war, crime and terrorism combined.

When an old agenda is done, people do not sit still. Harari predicts that humanity will turn to three new projects:

• Immortality: treating death as a technical problem to solve. He calls the effort to defeat death the Gilgamesh project, after the Sumerian king who searched for eternal life.
• Bliss: engineering lasting happiness. Evolution made pleasure fleeting, so the push is to change body chemistry directly, through drugs, genetics and brain technology.
• Divinity: upgrading humans into gods, with powers of creation and control over their bodies and the world. This is the "Homo Deus" of the title.

Harari stresses that these are not prophecies. They are the likely goals of a species that has always pursued more health, more happiness and more power. He also describes a paradox of historical knowledge: the more people learn about predicted futures, the more they change their behavior, so forecasts defeat themselves. The point of studying history, in his view, is not to predict the future but to free people from the past and show them that other futures are possible. He illustrates this with the lawn. The green lawn began as a status symbol of European aristocrats, who could afford land that grew no food. Once you know that story, a suburban lawn looks like a choice, not a law of nature.

How Sapiens conquered the world

Part I asks what makes humans special and how they came to dominate the planet. Harari begins with animals. He argues that farm animals such as pigs, cows and chickens have complex emotional needs, and that industrial farming ignores those needs on a massive scale. The agricultural revolution, he says, came with new religions that justified human control over other species. The theist religions placed humans above animals because only humans had souls and a direct line to God.

Harari then questions the idea of the soul and examines consciousness. Science has no clear account of why subjective experience exists at all. Life sciences increasingly describe organisms as algorithms: sets of biochemical steps that process inputs and produce outputs. If that view is right, then feelings are biochemical calculations that help animals survive and reproduce.

So what is the real source of human power? Not a soul and not a uniquely rich inner life. Harari's answer, carried over from his earlier book Sapiens, is that humans can cooperate flexibly in very large numbers. Chimpanzees cooperate in small groups that know each other. Ants and bees cooperate in large numbers but rigidly. Humans can coordinate millions of strangers because they share stories.

The web of meaning

Part II explains how those shared stories work. Harari distinguishes three levels of reality:

• Objective reality: things that exist whether or not anyone believes in them, such as radioactivity.
• Subjective reality: things that exist in one person's mind, such as a personal pain.
• Intersubjective reality: things that exist because many people believe in them together, such as money, nations, gods, laws and corporations.

Intersubjective entities are fictions, but they are powerful fictions. When writing and bureaucracy appeared, they reshaped real life. Harari points to ancient Egypt, where the pharaoh and gods such as the crocodile god Sobek were imagined beings, yet officials taxed peasants and built canals in their name. Written records let institutions grow larger than any human memory, and paper reality often overruled physical reality.

Harari then turns to the relationship between science and religion. He calls them an odd couple. Religion, in his definition, is any system of human norms and values that claims a superhuman authority. Science deals with facts and cannot by itself produce ethical judgments. So the two often cooperate in practice. Modern institutions use science for power and some form of religion or ideology for meaning.

The modern covenant and humanism

Modern culture, Harari argues, rests on a deal he calls the modern covenant: humans agree to give up meaning in exchange for power. Premodern people believed the universe had a cosmic plan that gave life meaning but limited what humans could do. Moderns reject any fixed plan. Life has no script, but humans can do anything they have the power to do.

The engine of this covenant is economic growth. The modern economy runs on the belief that the pie can keep expanding, which lets credit, science and production feed each other. Growth softens conflict, because people can get richer without taking from others. It also creates new risks, such as ecological collapse, and a constant pressure to keep growing.

If the universe has no meaning, where does modern life get its meaning? Harari's answer is humanism. Humanism, in Harari's account, is a religion that worships humankind. It holds that human experience is the source of meaning and authority. Where medieval Europeans looked to scripture, humanists look inward. Harari summarizes the shift in simple formulas:

• Medieval knowledge: Knowledge = Scriptures × Logic.
• Scientific knowledge: Knowledge = Empirical Data × Mathematics.
• Humanist ethics: Knowledge = Experiences × Sensitivity.

Under humanism, voters know best in politics, customers are always right in economics, beauty is in the eye of the beholder in art, and "if it feels good, do it" in ethics, as long as nobody else is hurt. Education teaches people to think for themselves.

Harari describes three branches of humanism that fought each other through the twentieth century:

• Liberal humanism puts the free individual and individual experience first.
• Socialist humanism says individual feelings are shaped by others and puts collective experience and equality first.
• Evolutionary humanism, which inspired the Nazis, said humans are unequal and that conflict should improve the species.

Liberal humanism won the twentieth century. Harari argues that its victory may be short. The same science that gave humans power now undermines the beliefs liberalism depends on.

Homo sapiens loses control

Part III is the core of the book. Liberalism rests on the belief that each person is a free, unified individual with an authentic inner voice. Harari argues that modern life sciences undercut all three ideas.

First, free will. Brain science describes decisions as the result of neural processes that are either deterministic or random. Neither is free in the liberal sense. People feel that they choose, but they do not choose their desires.

Second, the unified self. Split-brain studies show that the two hemispheres can act on different information while one side invents a story to explain what the other did. Harari also draws on Daniel Kahneman's distinction between the experiencing self, which lives moment to moment, and the narrating self, which remembers, evaluates and makes decisions. In Kahneman's cold-water experiment, people who held a hand in cold water for a longer trial, with a slightly less cold ending, chose to repeat the longer trial. The narrating self judges by peaks and endings, not by total experience. So the "inner voice" liberals trust is a storyteller that often misrepresents what happened.

Third, Harari argues that the coming century will produce a great decoupling: intelligence will separate from consciousness. For most of history, only conscious beings could do intelligent tasks. Now non-conscious algorithms can drive cars, diagnose disease and trade stocks. The economy needs intelligence, not consciousness.

This leads to three threats to liberalism:

• Humans may lose their economic and military usefulness, creating what Harari calls a useless class of people with no economic role.
• The system will still value humans as a collective but not as unique individuals.
• A small elite of upgraded superhumans may emerge and leave everyone else behind.

He points to a shift in authority. As algorithms gather data about people's bodies and behavior, they may come to know people better than people know themselves. He cites Angelina Jolie's decision to have a preventive mastectomy after a genetic test showed a high cancer risk from a BRCA1 mutation. She acted on what an algorithm reported about her genes, not on how she felt. As this pattern spreads, Harari argues, people will hand decisions about health, careers and partners to systems that read them more accurately than their own narrating selves.

The new religions: techno-humanism and Dataism

Harari describes two "techno-religions" that may replace liberal humanism.

Techno-humanism keeps humans at the center but wants to upgrade them. It accepts that Homo sapiens has had its day and aims to create Homo Deus: humans with improved minds, through brain-computer interfaces, genetic engineering and drugs. Harari warns that this approach has a basic problem. If technology can reshape human desires, then human desires can no longer serve as the final authority. Techno-humanism may end up upgrading people into whatever the market or the state finds useful, while their ability to feel and imagine shrinks.

Dataism is more radical. It says the universe consists of data flows, and the value of any phenomenon depends on its contribution to data processing. Organisms are algorithms. Societies are data-processing systems. Harari reinterprets history this way. Capitalism beat communism because distributed processing works better than centralized processing in a fast-changing world. Democracy and dictatorship are competing ways to collect and analyze information. Human history itself is a process of linking more processors into larger networks.

For Dataists, the highest value is freedom of information. The ultimate project is an Internet-of-All-Things that absorbs everything. Dataism's moral advice is simple: record and connect everything, and let the algorithms decide. If the system succeeds, Harari argues, humans may become just one more part of a larger data network, and then a part that is no longer needed.

Harari ends without a verdict. He states again that the scenarios are possibilities, not prophecies, and he leaves the reader with three questions:

1. Are organisms really just algorithms, and is life really just data processing?
2. What is more valuable: intelligence or consciousness?
3. What will happen to society, politics and daily life when non-conscious but highly intelligent algorithms know us better than we know ourselves?

What the critics say

Reviewers praise the scope but question the method. Many biologists and philosophers reject the claim that organisms are "just algorithms," and they argue that Harari treats a contested metaphor as settled science. Others say he overstates what neuroscience shows about free will and the self. Critics also point out that his sweeping claims about history, religion and humanism rely on broad generalizations rather than detailed evidence, and that his account of the decline of famine, plague and war looked too confident after the COVID-19 pandemic.

Who should read it

Read it if you want a big-picture frame for thinking about AI, biotechnology and the future of work. It suits readers who enjoyed Sapiens and want its ideas pushed forward. Treat it as a set of provocations, not forecasts.