In Sapiens, Yuval Noah Harari uses concepts from physics, chemistry, biology, and history to tell the story of us, Homo sapiens.
Our history is punctuated by four major revolutions: The Cognitive Revolution, the Agricultural Revolution, the Industrial Revolution, and the Scientific Revolution. Part I (Chapters 1-4) explores the Cognitive Revolution and the events leading up to it.
We’ll look at each revolution and how it dramatically redirected the course of human history, but to understand these upheavals, we need to go back to a time when Homo sapiens was just one of multiple human species (and not a very distinguished species, at that).
We think of our own species as the only humans, distinguished from and superior to every other species on earth. But when we, Homo sapiens, arrived on the scene 2.5 million years ago, we weren’t anything special. We existed in the middle of the food chain, as often prey as we were predators, and we weren’t even the only humans.
Humans evolved in East Africa from a genus of apes. These early humans settled all over the world, and as the climates and conditions differed from place to place, they acquired different traits and became different species.
We tend to think of the evolution of humans as a linear progression from Homo erectus to Neanderthals to Homo sapiens, but at least six human species were alive when our own lived on earth, and others may yet be discovered. The known human species included Homo soloensis, Homo floresiensis, Homo denisova, Homo rudolfensis, and Homo ergaster. The three that will play the biggest roles in this book are:
1. Homo neanderthalensis (“Man from the Neander Valley”): Also known as Neanderthals, these humans lived in western Asia and Europe. They were more muscular than we were and they had bigger brains than we did (or do today). We’ll see why the Neanderthal species died out, even though Neanderthals were superior to Sapiens in many ways.
2. Homo erectus (“Upright Man”): These humans lived in eastern Asia for almost 2 million years, making them likely to be the longest-living human species ever. (As we’ll see, it’s unlikely that Homo sapiens will be around 2,000 years from now, let alone 2 million.)
3. Homo sapiens (“Wise Man”): Us. Our species of man also evolved in East Africa.
Throughout, the term “Sapiens” refers to our own species while the term “human” refers to all the members of the Homo genus.
Of the eight known human species, only one survived. Before we discuss how Sapiens became the dominant humans, let’s look at what all the human species had in common.
Mammals that are 130 lbs typically have a brain that’s an average of 12 cubic inches. In contrast, the brains of early humans were 36 cubic inches. Today, our average brain size is 73-85 cubic inches, and the brains of Neanderthals were even bigger than ours.
It seems like large brains would give us and our fellow humans an obvious advantage over other animals, but it wasn’t necessarily an asset to early humans.
Big brains take a lot of energy to fuel. Our brains make up 2-3% of our body weight, but use 25% of our energy. (The brains of our ape siblings only use 8% of their energy.)
This drain of energy caused two main problems:
When you’re in the middle of the food chain, trying to catch small animals and keep out of the way of big ones, using your energy to power your brain instead of your muscles isn’t the smartest strategy.
We still don’t really know why we evolved such large brains when there was little use for them in early history. It was a bad use of our energy.
Like having a big brain, walking upright seems like an unequivocally positive trait to us today, in part because we still walk upright and can’t imagine moving any other way. There were both advantages and disadvantages to walking upright.
Pros:
Cons:
Narrow hips especially had far-reaching consequences for humans, creating a domino effect that led to helpless babies. This was because the women who survived the dangerous activity of childbirth (and continued to pass on their genes through subsequent births) were the ones who gave birth early in the fetus’s gestation, when the baby’s head was smaller and undeveloped.
Consequently, women evolved to give birth earlier when the fetus is less developed. This means that human infants are undeveloped and helpless compared with other animal infants. For instance, a colt can start to run soon after birth, and a kitten finds food on its own after a few weeks. But human children are dependent on their parents for years.
The fact that human children were vulnerable for years after birth meant that human adults had to care for and protect them for years. Like having a big brain, this wasn’t an obvious advantage for early humans. They needed their energy for activities like escaping the jaws of larger, stronger animals.
Despite the risks involved in caring for vulnerable infants, their existence created unique social situations for humans. These situations and the resulting societal bonds may have contributed to the rise of human dominance in the animal kingdom.
There were two unique results of human children being born prematurely:
Result #1: The “It Takes a Village” Mentality: Because children were so helpless, mothers relied on family members and neighbors to raise them. Many other animal genera (plural of “genus”) didn’t have the need to form these social bonds.
Result #2: The Potential for Socialization: Children born relatively helpless are (relative) blank slates. As such, their societies can shape them through education and socialization to be whatever they want them to be. Whereas other mammals are born like glazed earthenware coming out of the kiln (if you try to reshape them, they’ll break), humans are born like molten glass, easily formed and reformed.
We shared much in common with our fellow humans. How did we rise from the middle of the food chain to the top? And how did we become the last humans standing?
The domestication of fire changed the game, giving humans power over the natural world that no other animal possessed. Fire was a source of light. It was warmth in the cold months and a weapon in moments of conflict. You could even use fire to burn through impassable underbrush, changing the landscape to fit your needs.
The most important use of fire was cooking. Cooking food made it easier to digest. Since digestion was easier, the long intestine became shorter. This development was especially important. Big brains and big intestines both use a lot of energy. By allowing humans to better digest food and evolve shortened intestines, fire may have indirectly contributed to the brain getting a greater share of the body’s energy. As the brain got more energy, it got bigger.
When humans mastered fire, they finally gained a key to developing dominance over animals that were stronger and faster than they were.
Sapiens wasn’t the only species that used fire. Why did it come to dominate?
Early theories suggested that either A) Sapiens bred with other humans, merging the various human species, or that B) Sapiens were too genetically different from other species to procreate with them, meaning that all humans currently alive are pure sapiens.
Both of these theories are flawed. For years, Theory B had more archeological evidence to support it. But then the results of a 2010 project to map the Neanderthal genome showed that 1-4% of Middle Eastern and European DNA is Neanderthal DNA. A few months later, results from an analysis of the DNA of newly-discovered Denisova showed that 6% of Melanesian and Aboriginal Australian DNA is Denisovan DNA. These results are still new and need to be confirmed. Even if they are confirmed, they don’t suggest a “merger” of genes as in Theory A—such small percentages hardly suggest that two species of humans “merged.” What they do suggest is that a small amount of interbreeding happened, enough that we still harbor the DNA of another species, but it was rare.
The current evidence leaves us with two options to explain the disappearance of other humans.
What made Sapiens the superior species that pushed other humans to extinction? Harari argues the most likely answer is language. We’ll cover that next.