Every schoolboy has been told that, to understand human nature, we must look to our closest genetic relatives—the chimpanzees. Jane Goodall's pioneering research revealed that chimps use tools, hunt cooperatively, and engage in violent activity that looks like warfare. And from these observations, she and generations of scientists who followed in her wake have concluded that humans are essentially advanced primates, and that our behaviors—from violence to sexuality—flow from this genetic inheritance. But what if this foundational assumption is wrong? The Primate Myth: Why the Latest Science Leads Us to a New Theory of Human Nature is a new book by the playwright and critic Jonathan Leaf. Based on vast quantities of scientific literature, Leaf argues that recent genetic and neuroscientific discoveries are overturning decades of conventional wisdom. A landmark study published in April 2025 revealed that humans share only 86.5 percent of our genes with chimpanzees—not the 98.6 percent we've long believed. More importantly, the differences are concentrated precisely where they matter most: in the structures of our brains that govern cooperation, empathy, and language. Leaf's thesis is both scientific and moral. If humans are not primarily aggressive primates but rather cooperative pack animals—closer in crucial ways to dolphins and wolves than to chimps—then it's high time to reconsider the natural impulses that lie at the roots of war, family, and human flourishing. Leaf joins Mosaic's editor Jonathan Silver to discuss his book and its implications.