THE QUESTION LIBRARY LIFE IN THE UNIVERSE
Similar genes can contribute differently when their activity changes in amount, location or timing. DNA similarity alone does not describe how those genes are used.
WHERE THE EVIDENCE STANDS
Humans and chimpanzees inherited much of their DNA from a shared ancestor. Similar DNA can produce different bodies when some protein instructions and patterns of gene activity differ. A similarity percentage also depends on what was compared.
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DNA is written in chemical letters. In the 2005 chimpanzee genome comparison, researchers reported about 1.2% single-letter differences in high-quality regions they could line up with human DNA. That figure describes those aligned regions, not every kind of difference across two complete genomes.
Other changes add, remove or duplicate stretches of DNA; rearrangements alter organization. Those require different comparisons. Before using a percentage, ask which sequences were included and whether missing or extra stretches were counted. A sequence score is not a percentage measure of differences in anatomy or behavior.
Protein-coding DNA supplies instructions for proteins. Changes there can alter amino acids, their building blocks. Many corresponding human and chimpanzee proteins are similar, but their instructions are not all identical.
Gene regulation controls where, when and how much genes are active. Cells use these controls during development and in response to their surroundings. The same gene can therefore contribute differently depending on the tissue, developmental stage or amount of its product. Comparing letters alone does not capture that activity.
During development, changing a gene’s activity can change when or where its product is available. Timing and location are therefore part of understanding how a body forms. This is a general mechanism, not proof that one particular regulatory change explains every difference between the species.
No. Humans and chimpanzees are branches of a family tree, descended from an earlier shared population. Chimpanzees and bonobos are our closest living relatives. Each living lineage has its own evolutionary history; a modern chimpanzee is not an unchanged version of our ancestor.
For the related question within our species, see how closely related all humans are.
How closely related are all humans?
Very closely.
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