Scientists Explain: If Humans and Chimps Share Up to 99% of Their DNA — Then Why Are We So Different?

Scientists believe that humans and chimpanzees or chimps share up to 99% of their DNA, which simply implies that we are closely related as a species. But this number is so high, yet the differences are so vast, that people usually ask, Why are we so different if we are so similar.

From physical appearance and natural behavior to sheer intelligence and cognition, humans and chimps are observably very distinct. However, the reason lies not in the DNA we share, but in how our genomes are regulated and expressed. These mechanisms create countless tiny changes and modifications that add up to the difference we can see today between the species.

The Real Difference: More Than One Percent

It is often cited that humans and chimps are 99% similar, but this only accounts for the protein-building genes and not the other factors, such as DNA sequences in charge of gene insertion, deletion, and duplication. If all of those are factored in, the right number is usually closer to 2–4%, but in some cases could still reach 1%.

Another misconception is the underestimation of how these small percentages could have such huge impacts on a species. For example, humans are estimated to have about 689 genes that chimps do not have. Each one of them characterizes a specific change to the human body and biology, which cumulatively will make up what makes us so different than our closest living relative.

Read more: WIRED | BMC Genomics

Gene Regulation: How DNA Gets Used

Are We Really 99% Chimp?

The information in our DNA or the gene’s code could be a lot similar to that of chimpanzees, but the big difference comes from how and when it’s expressed. We know that humans are a lot smarter than chimps, and one of the reasons is that we express thousands of genes differently in the human brain alone.

This affects our cognitive functionalities, such as the ability to think abstractly and the use of language. There are many more micro tweaks in how our genes are being regulated compared to chimps, despite the similarities in the genes’ code. Ultimately, the point is, how DNA is used is one of the biggest factors why we are so different than them.

Copy Number Changes and Chromosomal Differences

Humans and chimps also differ in the number of copies each gene has. This is important because it directly influences the amount of protein produced, which will therefore lead to a significant variation in phenotype, the set of observable characteristics within a species.

One great example is the development of the brain, where humans have more gene families that are duplicated and deleted for brain growth. It is also one of the driving forces of the evolution of the human brain. This is because those duplicated genes could mutate or acquire new functionalities, increasing the complexity of the organism.

Read more: Wikipedia

Epigenetics: The Hidden Code

The DNA of humans and chimps may be similar for up to 99% but beyond this lies the layer of epigenetic regulation, which refers to heritable changes in gene expression without editing the original DNA sequence. In other words, even identical genes can behave entirely differently in two organisms, based on their epigenetics.

Due to the way we evolved, humans and chimpanzees have spent thousands, if not millions, of years in different environments. And the changes in epigenetics could be heavily influenced by these factors, such as diet, stress, and living conditions.

Are Chimp and Human DNA 99% the Same?

Author's Final Thoughts

Even with up to 99% similarities in DNA, humans and chimps are visibly different when you compare them side by side. The observable characteristics are distinct thanks to a number of processes inside our body, such as gene structure, regulation, duplication, and epigenetics, that are unique and define what makes us human beings.

Read next: Why Did Ancient Humans Start Using Fire? — New Theory Says It Wasn’t Just for Cooking

References & Further Reading

Chimpanzee Sequencing and Analysis Consortium. (2005). Initial sequence of the chimpanzee genome and comparison with the human genome. Nature. https://www.nature.com/articles/nature04072

King, M.-C., & Wilson, A. C. (1975). Evolution at two levels in humans and chimpanzees. Science. https://www.science.org/doi/10.1126/science.1090005

Cáceres, M., Lachuer, J., Zapala, M. A., et al. (2003). Elevated gene expression levels distinguish human from chimpanzee brains. PNAS. https://www.pnas.org/doi/10.1073/pnas.2135499100

Kronenberg, Z. N., Fiddes, I. T., Gordon, D., et al. (2018). High-resolution comparative analysis of great ape genomes. Science. https://www.science.org/doi/10.1126/science.aar6343

National Human Genome Research Institute. (2005). New genome comparison finds chimps, humans very similar at DNA level. NHGRI. https://www.genome.gov/15515096/2005-release-new-genome-comparison-finds-chimps-humans-very-similar-at-dna-level