The science of evolution is central to Harari’s arguments in Unstoppable Us. Harari suggests that humanity’s “unstoppable” nature is not innate but that our world domination is the result of evolutionary changes and humanity’s ability to adapt to specific circumstances. Harari teaches his readers that this trajectory comes with consequences, both good and bad.

In developing this theme, Harari draws closely on the work of 19th-century naturalist and biologist Charles Darwin. Darwin first articulated the biological theory of evolution that shapes Harari’s book. This theory holds that organisms, including humans, are the products of natural selection. Organisms with superior traits or skills survive and reproduce, leading to the evolution of various species. To support this, Harari gives evidence that some of our modern biological instincts are legacies of evolution, an example of which is our urge to eat fatty, sweet foods even though our bodies do not always need them. Our ancestors, however, needed to consume sweet and fatty foods when they foraged because they did not know when their next meal might come. It was a survival method that persists in our neurobiology today.

Harari establishes his theme by explaining the evolutionary process, using whales as an example: