The Third Chimpanzee

Introduction: Our Place in the Animal World

Humans are both unique and deeply embedded in the animal kingdom. While we possess distinct traits like complex language and art, our genetic makeup is remarkably similar to other mammals. We share more than 98 percent of our genetic material with chimpanzees, making them our closest living relatives. Jared Diamond developed this perspective by combining his knowledge of anatomy, evolutionary biology, and geography to apply the rules of the natural world to human history.

To uncover these deep biological relationships, researchers use a method known as a molecular clock. This process relies on the fact that the internal code of every living thing changes slowly and at a steady rate over millions of years. By measuring these genetic changes, scientists determined that humans and chimpanzees began evolving on separate paths only about seven million years ago. From a purely biological standpoint, humans could easily be classified as a third species of chimpanzee.

This close biological relationship creates difficult ethical questions about how we treat our closest animal relatives. Medical testing on chimpanzees is often defended because their bodies react so much like ours, but this exact similarity makes the practice feel wrong to many people. We generally agree that it is unacceptable to experiment on humans or keep them in cages, yet we routinely do these things to animals that share almost all of our traits. Deciding where to draw the line between humans and other animals is a major challenge that society must face as we learn more about our shared origins.

The massive differences we see between humans and chimpanzees come from a tiny fraction of our genes. Only about 1.6 percent of our genetic code is completely unique to us. Small changes in just a few genetic instructions can lead to major shifts in how a body is built or how a brain functions. In humans, these small genetic tweaks likely reshaped the voice box and reorganized the brain, providing the foundation for everything that makes us distinct from the rest of the animal world.