It’s often said that humans and chimps share 99% of their DNA. That means a lot less than almost everybody believes it means

Early research suggested that human and chimp genomes are more than 98% identical. “What it means is that for each part of the human genome where the chimp has a corresponding DNA sequence, on average 1 out of 100 nucleotides (single A, C, T or G bases) is different,” explained Katie Pollard, director of the Gladstone Institute of Data Science and Biotechnology at the University of California, San Francisco.

…

But the 99% figure is misleading because it focuses on stretches of DNA where the human and chimp genomes can be directly aligned and ignores sections of the genomes that are difficult to compare ….

Sections of human DNA without a clear counterpart in chimp DNA make up approximately 15% to 20% of the genome ….

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So, while earlier studies suggested a 98% to 99% similarity, comparisons that include harder-to-align regions push that difference closer to 5% to 10% ….

In fact, a 2025 study found that human and chimpanzee genomes are approximately 15% different when compared directly and completely.

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