"Humans and chimpanzees share 98% of their DNA" is one of the most widely repeated statistics in popular science — and it's also one of the most widely misunderstood. The real number depends entirely on what, exactly, you're measuring and how you count the differences, and the answer is more interesting than a single tidy percentage.
The commonly cited 98–99% similarity figure comes from comparing single-nucleotide positions across the regions of the human and chimpanzee genomes that align cleanly with one another — essentially, letter-by-letter spelling differences in the shared portions of DNA. When researchers restrict the comparison strictly to these alignable single-letter substitutions, humans and chimpanzees differ at only about 1–1.2% of positions, giving the familiar 98.8%-or-so similarity figure.
That figure only tells part of the story. Genomes don't just differ through single-letter substitutions — they also differ through insertions and deletions, where entire chunks of DNA are present in one species but missing in the other. When researchers include these structural differences in the comparison, overall genome similarity estimates drop to somewhere in the 95–96% range. Neither number is "wrong" — they're simply measuring different things, which is exactly why you'll see both 98% and 95% cited as "the" similarity figure in different sources.
Because chimpanzees and bonobos are themselves each other's closest living relatives, having only split into separate species roughly 1–2 million years ago, humans are almost equally closely related to both. Genetic studies put human similarity to bonobo DNA at essentially the same level as to chimpanzee DNA, around 98.7% using comparable methods — meaning neither the common chimpanzee nor the bonobo can really be called "more human" than the other.
Moving further along the great ape family tree, humans share somewhat less DNA with gorillas, whose lineage split from the human-chimp-bonobo branch around 9–10 million years ago, and less again with orangutans, whose lineage diverged even earlier. Estimates commonly place human-gorilla similarity in the high-90s percent range and human-orangutan similarity a little lower still, tracking neatly with how much earlier each lineage branched off the shared ancestral tree.
Here's the part that often surprises people: humans share around 85% of DNA with mice, and even roughly 60% of protein-coding genes with fruit flies. That's because a huge proportion of any animal's genome codes for basic cellular machinery — how cells divide, process energy, and build proteins — that's been conserved across hundreds of millions of years of evolution because it simply works. A high percentage shared with a distant species isn't a sign of closeness; it's a reminder that life shares deep, ancient machinery, and it's the remaining fraction, along with differences in when and how genes are switched on, that accounts for the dramatic differences between a human and a mouse, or a human and a chimpanzee.
The high degree of genetic overlap between humans and chimpanzees helps explain why chimpanzees are used as a comparative model in biomedical and cognitive research, why chimpanzee anatomy and physiology so closely mirror our own, and why so many chimpanzee behaviours — tool use, long-term social bonds, grief responses, and political alliance-building — look recognisably similar to human behaviour. It's also a big part of the ethical case for chimpanzee conservation: protecting a species this closely related to us carries a weight that's hard to separate from our own sense of kinship.
So is it 98% or 95%? Both figures are legitimate, depending on method — 98–99% reflects single-letter differences in directly alignable DNA, while 95–96% reflects a broader comparison that also accounts for larger insertions and deletions between the two genomes.
Are humans more closely related to chimpanzees or bonobos? Essentially equally related to both — chimpanzees and bonobos split from each other only 1–2 million years ago, long after both had already diverged from the human lineage.
Does sharing so much DNA mean chimpanzees think like humans? Not exactly — shared DNA explains a lot of shared biology and some shared cognitive and social traits, but chimpanzees have their own distinct cognition, culture, and communication shaped by millions of years of independent evolution since our lineages split.
When did humans and chimpanzees last share a common ancestor? Genetic and fossil evidence points to a split somewhere between 6 and 7 million years ago, after which the human and chimpanzee-bonobo lineages evolved independently, accumulating the genetic differences measured today.
BCCP monitors six wild chimpanzee communities in the Budongo–Bugoma Corridor, each with its own named members and story. Meet the chimps we protect and follow their lives.
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