What Does it Really Mean to Be 99 Percent Chimp?

On the animal family tree, chimpanzees (Pan troglodytes) are our closest living relative. We share similar life cycles, some underlying biology and a lot of DNA — 99 percent based on the sequencing of the chimp genome in 2005. A 2012 study suggests that we share a similar percentage with bonobos, compared to 98 percent with gorillas. But when we look at chipms, we see a completely different organism. So, how does a measly one or two percent produce such vastly varied organisms?

As Emily Elert explains in the Minute Earth video above, it's hard to know what 99 percent similarity really means, especially when you take into account that humans also share 50 percent of their DNA with bananas and 80 percent with dogs.

Quantifying differences in DNA is tricky. Over millennia, the chimp genome and the human genome have each changed a lot. Some mutations involved swapping out one base pair (the basic unit of DNA) for another, while others entailed shifts and repeats of massive sections of DNA. And that doesn't even take into account the fact that the same section of DNA can be read and translated in different ways.

When comparing human and chimp DNA, researchers only looked at single base pair changes. That's where they got the 99 percent, Elert explains. So while the number might seem really big, the similarities we share with chimps on a genetic level can tell us a lot about how humans evolved to look and act so differently than even our closest relations.

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Helen Thompson writes about science and culture for Smithsonian. She's previously written for NPR, National Geographic News, Nature and others.