HUMANS AND APES: WHY DO WE SHARE 98% OF OUR DNA?

A chimpanzee’s face can feel familiar before a single genome is examined. The resemblance has a deeper explanation: humans, chimpanzees and bonobos inherited much of their biology from common ancestors. The famous claim that we share 98–99% of our DNA captures part of that relationship. It does not mean that two complete genomes are identical except for a neatly defined remaining percentage.

The essential qualifier is alignment. NHGRI’s account of the 2005 comparison described directly comparable human and chimpanzee sequences as almost 99% identical. Its broader calculation, including insertions and deletions, was 96%. Those are different summaries of a historical comparison, not competing measurements of one universal quantity.

Illustration: the hero is an AI-generated conceptual image of a human, a chimpanzee and a DNA motif. It is not a photograph of a genetic experiment, an identified research participant or an ancestral individual.

What does 98–99% actually measure?

DNA is a sequence written in four chemical bases, conventionally abbreviated A, C, G and T. Sequencing reads their order. Comparing genomes then requires finding corresponding stretches inherited from the same ancestral regions. In a matched stretch, researchers can count positions where one base differs. That is one useful definition of sequence identity. NHGRI explains the sequencing process.

But evolution also adds or removes stretches, duplicates genes, reverses segments and changes repetitive DNA. A base-by-base comparison of alignable regions cannot summarize all those events. Results depend on the reference genomes, which regions are included, alignment rules and treatment of gaps. The original chimpanzee genome paper compared draft assemblies, not two perfect inventories of every sequence in every member of either species.

Chimpanzees, bonobos, gorillas and orangutans

Chimpanzees and bonobos, the two living species of Pan, are equally our closest living relatives in the species tree. The 2012 bonobo genome study found 98.7% identity to human DNA and 99.6% to chimpanzee DNA in corresponding single-copy autosomal regions. Those values have a stated denominator. They are not percentages of personality, intelligence or total biological similarity, and should not be mixed uncritically with estimates from other methods.

A common ancestor, not a modern chimpanzee

The Smithsonian’s genetic overview places the human–chimpanzee common ancestor approximately 8–6 million years ago. The interval is an estimate, not a dated meeting between two individuals. Fossils and genetic models constrain the history in different ways. Both descendant lineages continued evolving. A modern chimpanzee is therefore a relative, not an unchanged portrait of our ancestor. The 2025 complete-genome study’s model estimated a human–chimpanzee split of 5.5–6.3 million years ago. Different mutation-rate assumptions, models and sampled regions help explain why estimates vary. The broader 6–8-million-year framing should not be treated as an exact date. 2025 genomic model.

Evolution is a branching history, not a ladder with humans at its inevitable summit. Chimpanzees and bonobos separated from one another later, approximately two million years ago in the bonobo study’s reconstruction. Gorillas and orangutans also have their own evolutionary histories. “Why are there still apes?” is answered by the same principle that allows related species to coexist: one surviving branch need not replace another.

Chromosome 2: a visible signature of ancestry

Humans normally have 46 chromosomes, while other living great apes have 48. Human chromosome 2 corresponds to two ancestral chromosomes that fused. A 1991 molecular study identified opposing telomeric repeat sequences inside the chromosome, where an ancient junction would be expected. Later analysis of the fusion region reinforced the correspondence with ancestral chromosome ends. One centromere remained active; the other was inactivated.

Shared biology, different development

Shared ancestry helps explain the same basic arrangement of organs and limbs, and conserved cellular machinery for growth, metabolism and DNA maintenance. Many corresponding genes participate in similar biological processes. Yet a gene list is not a blueprint that develops independently of context. Comparative genomics studies conserved sequences and their functions, including regulatory regions that influence when and where genes are used.

Changes to protein sequences, gene dosage, regulatory switches and developmental timing can matter without replacing most of the genome. A 2019 study of brain organoids compared human, chimpanzee and macaque development at single-cell resolution, identifying differences in maturation and gene regulation. Organoids are laboratory models of aspects of development. They do not reproduce an entire brain, a culture or a capacity for language.

A Science experiment in 2020 showed that expression of the human-specific gene ARHGAP11B increased neocortical size and folding in fetal marmosets. This is evidence for a developmental mechanism in an experimental setting, not a demonstration that a gene makes an animal human or confers human intelligence. Brain evolution involves interacting changes; language and cognition cannot be reduced to a single DNA percentage or one molecular switch.

From genetic change to Homo sapiens

Mutations supply variation; their fate depends on more than usefulness. Natural selection can favor heritable variants that affect reproductive success in a particular environment. Genetic drift also changes variant frequencies through chance, especially in small populations. Migration and demographic history matter too. It is therefore incorrect to assume that every difference between a human and a chimpanzee was selected because it helped produce modern human abilities.

The emergence of Homo sapiens is much more recent than the human–Pan split. The Jebel Irhoud fossils combine a relatively modern facial form with a more elongated braincase; associated heated flints were dated to about 315,000 years ago, with uncertainty of ±34,000 years. They help document early sapiens evolution, not the six-million-year-old common ancestor. Read our Jebel Irhoud feature for the discovery’s context.

What the percentage cannot tell us

“Humans are not apes” confuses an everyday word with biological classification: humans belong within the great apes. “The remaining 1–2% explains everything human” mistakes a comparison statistic for a causal explanation. “Chimpanzees stopped evolving” mistakes a living relative for a fossil. And “more similar DNA means identical minds” overlooks development, bodily organization, learning and environment. Each claim asks a percentage to answer a question it was not designed to measure.

Our place in nature is neither erased by the similarities nor fully explained by the differences. Genetic evidence puts humans inside an old, branching family of primates. It also gives researchers precise questions to investigate: which changes affect development, which reflect demographic history, and how do they interact? The strongest conclusion is not that humans are “98% chimpanzee.” It is that shared ancestry leaves measurable traces, and that those traces require careful interpretation.