Unstoppable Us, Volume 1: How Humans Took Over the World

Creationism is a form of religious belief, most commonly held by some sects of the Christian, Jewish, and Islamic religions. Creationism asserts that the universe was created by God in its current form and refutes modern evolutionary science. It holds that the Old Testament story of the creation in the Book of Genesis, in which God created the universe in seven days, is literal truth. This narrative presents mankind as God’s last and best creation, separate from animals and with a special religious and moral purpose. 

Until the scientific advances of the 1800s, creationism was the most commonly held theory of human origins, supported by religious teachings and prevalent ideas of human exceptionalism and superiority over the natural world. In the 1800s, the studies of the biologist Charles Darwin and others challenged creationism by showing that all species—including humans—had evolved over millions of years through the process of natural selection. Evolutionary theory is now the most accepted and evidenced theory for the origins of life, especially among the international academic community. In the United States, creationism remains a widely held belief, especially in Evangelical Christian communities.

DNA (deoxyribonucleic acid) is an organic substance found in all living material. DNA contains the genetic instructions for all organisms and some viruses; it determines the development, function, growth, and reproduction of all living things. DNA is located in the nucleus of each cell and is made up of two twisted strands, forming a double helix. Individual instructions—such as for eye color—are contained in different sections of these strands, known as “genes.” When most organisms, including humans, reproduce, two strands, one from each parent, are mixed together to form the DNA of their offspring. 

By mapping the complete DNA of individuals or species, known as “genomes,” scientists can measure the genetic relationship between them. For instance, the genome found in Neanderthal remains has shown that Neanderthals and Sapiens are roughly 20% related and almost certainly interbred when they lived contemporaneously. The ability to compare genomes has provided microbiological evidence for the evolution of species, as it shows the process by which DNA is adapted through generations over time.

Floresians (Homo floresiensis) were a species of humans who lived on the island of Flores, Indonesia, approximately one million years ago. They became extinct when exposed to Sapiens about 50,000 years ago. Floresians were the smallest known human species, standing at only around one meter in height. Harari supports the widely held theory that Floresians evolved to be small because they became isolated on Flores as a result of sea-level changes and adapted to need fewer resources as a result.

Modern humans are descended from the species of humans whom scientists call Homo sapiens, meaning “wise humans,” because of the adaptability and ingenuity Harari assesses in Unstoppable Us. However, Sapiens co-existed with, and later displaced, other groups of humans like Neanderthals. Nevertheless, DNA evidence from modern humans shows that Sapiens and Neanderthals bred, though we cannot know what led to this mixing.

“Megafauna” is a zoological term that refers to very large animals, all of which are now extinct. These include creatures like the wooly mammoth of the Arctic and many large animals unique to Australia, like giant kangaroos and koalas. Harari suggests that as Homo sapiens migrated all over the world, they not only caused the extinction of other human groups, like Neanderthals, but also unknowingly caused much of the world’s prehistoric megafauna to vanish. Their skills in cooperative hunting led to the depletion of these animals, which reproduced relatively slowly and could not adapt. Harari points out that their disappearance had long-term consequences for landscapes and other, smaller animals. For example, mammoths cleared snow from northern lands with their tusks, making grass available as a food source to other creatures. Their extinction meant that this grass remained snow covered and inaccessible to other animals who starved, as well as reducing the number of new spring plants that could grow. Harari’s discussion of Sapiens’ impact on ancient megafauna highlights the disastrous environmental impact of human actions.

Neanderthals were a species of humans who lived across parts of Europe and Asia during the Paleolithic Era (or Stone Age). It is believed that their species formed around 400,000 years ago and that they lived until their extinction around 40,000 years ago. Archeologists discovered the first Neanderthal remains in Germany’s Neader Valley during the 19th century and named the species after this location. Their remains show stocky forms that conserved heat during the ice ages of that period. According to Harari, Neanderthals became extinct due to their inferior socialization and lack of cooperative skills; although this is a widely accepted theory, there are different schools of thought on the reasons for their extinction. Homo sapiens depleted the natural resources on which Neanderthals relied as Sapiens spread across the globe. There may also have been violent clashes between the two species that contributed to the Neanderthal decline. Disease and climate change might have contributed to their disappearance as well. Archeological discoveries show that Neanderthal brains were larger than previous humans; they made fire, used stone tools, and created cave art. They may have possessed some skills of speech.