Genetic Similarity

Last updated: February 2, 2026

Decoding the remarkable DNA connections between humans and other great apes.

Introduction to Genetic Similarity

Our DNA¹ carries the genetic instructions for the development, functioning, growth, and reproduction of all known organisms. It's a long molecule composed of two chains that coil around each other to form a double helix. The sequence of the four nucleotide bases²—Adenine (A), Guanine (G), Cytosine (C), and Thymine (T)—encodes this information.

By comparing the DNA sequences of different species, scientists can quantify their genetic similarity. This comparison reveals how closely related species are on the evolutionary tree. The higher the percentage of shared DNA, the more recent their common ancestor.

Key Concept

Genetic similarity is measured by comparing the sequence of DNA bases between species using techniques like genome sequencing³. A high percentage indicates a close evolutionary relationship.

Human-Chimpanzee Similarity (~98.8%)

Humans and chimpanzees (including bonobos) are our closest living relatives. Genome sequencing projects have revealed an astonishing degree of similarity.

Overall Similarity

When comparing the alignable portions of the human and chimpanzee genomes, the DNA sequences are approximately 98.8% identical. This figure considers single-nucleotide differences⁴ (changes in a single DNA base).

Protein-Coding Genes

Even in the genes that code for proteins⁵ (the building blocks of our bodies), the similarity is remarkable. The average protein differs between humans and chimps by only about two amino acids⁶.

Considering Indels

If insertions and deletions (indels)⁷ of DNA segments are also factored in, the overall similarity is often cited as around 96%. However, the 98.8% figure accurately reflects the identity of the directly comparable sequences.

Differences arise not just from single base changes but also from:

• Insertions and Deletions (Indels): Segments of DNA that have been added or removed in one lineage compared to the other.
• Gene Duplications⁸: Some genes have been copied multiple times in one lineage.
• Regulatory Differences: Changes in non-coding DNA regions that control when and where genes are turned on or off (gene regulation⁹) are thought to play a significant role in the observable differences between humans and chimps.

Human-Gorilla Similarity (~98.4%)

Gorillas are the next closest relatives after chimpanzees. Their genome also shows a high degree of similarity to ours.

Overall Similarity

Humans share approximately 98.4% of their DNA sequence with gorillas in comparable regions.

Interesting Divergences

While most of the human genome is more similar to chimpanzees, about 15% of the human genome is actually more closely related to the gorilla genome than the chimpanzee genome. This phenomenon, known as incomplete lineage sorting¹⁰, reflects the complex branching patterns during the speciation¹¹ process.

Human-Orangutan Similarity (~97%)

Orangutans are more distantly related great apes compared to chimpanzees and gorillas, but the genetic similarity remains substantial.

Overall Similarity

Humans and orangutans share about 97% of their DNA sequence in comparable regions.

Slower Evolution?

Interestingly, the orangutan genome appears to have evolved more slowly than human and other African ape genomes, showing fewer large structural rearrangements over time.

Genetic Similarity Summary

The high degree of genetic similarity across the great apes is consistent with a shared evolutionary history.

What These Similarities Mean

The genetic similarities between humans and other great apes are used to understand evolutionary relationships and common descent¹².

• Common Ancestry: The hierarchical pattern of similarity (humans closest to chimps, then gorillas, then orangutans) matches the relationships indicated by anatomical studies and the fossil record. This pattern is consistent with divergence from a common ancestor over millions of years.
• Shared Genetic Elements: Comparisons reveal shared non-functional genetic elements, like pseudogenes¹³ (inactive gene copies) and endogenous retroviruses¹⁴ (remnants of past viral infections integrated into the genome), present in the same locations in related species. These shared genetic features are consistent with common inheritance.
• Molecular Clock: The degree of genetic difference generally correlates with the estimated time since divergence, acting like a "molecular clock¹⁵" (though its rate can vary). This allows scientists to estimate when different lineages split.

Summary

Genetic evidence, including high DNA sequence identity and patterns of shared genetic features (including non-functional elements), informs our understanding of the evolutionary relationship between humans and other great apes. Genomes contain layers of information that scientists use to reconstruct lineages and relationships between species.

While differences in gene regulation and specific gene functions account for the unique characteristics of each species, the foundational genetic similarity provides important data for understanding primate evolution.

References

1. DNA (Deoxyribonucleic Acid)
2. Nucleotide bases
3. Genome sequencing
4. Single-nucleotide polymorphism
5. Protein-coding gene
6. Amino acids
7. Insertions and deletions (indels)
8. Gene Duplications
9. Gene regulation
10. Incomplete lineage sorting
11. Speciation
12. Common descent
13. Pseudogenes
14. Endogenous retroviruses
15. Molecular clock

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