Are mutations always harmful, or can they help?

When can a mutation help?

In a 2016 bacterial study, some groups of related bacteria carrying new mutations outperformed their ancestor in one food medium. Most showed little detectable change or poorer performance. Each group carried several mutations, so the results do not identify every mutation’s individual effect. A change’s consequences depend on its surroundings.

Do some spots in our DNA change more often than others?

Yes. DNA is often described using four letters, A, C, G and T. The chance of a letter changing depends partly on nearby letters and the chemical state of the DNA. A study of human families found that sites where C sits beside G were especially prone to changes. Chemical tags called methyl groups help explain this pattern: they can make a C more likely to change into a T.

Repair matters too. Cells have systems that correct mistakes made while DNA is copied, but correction varies by location. In a yeast experiment, altering the letters beside a vulnerable site restored repair there. This shows why counting DNA changes requires attention to both how errors arise and how they are corrected. That experiment involved yeast; it does not supply a map of every vulnerable site in human DNA.

Could quantum effects inside DNA help cause mutations?

Possibly. A proton is a tiny particle found in hydrogen atoms. Protons help form bonds between paired DNA letters. Quantum tunnelling allows a proton to cross an energy barrier it could not cross in the usual classical picture. Moving protons can temporarily change a base’s chemical form and how it pairs.

A 2022 theoretical study predicted that tunnelling could contribute to this process. For a lasting mutation, the altered form would need to survive strand separation, lead to an incorrect pairing during copying and escape correction. Its biological contribution remains an open question.

For experiments about how evolutionary histories repeat, see our answer on replaying evolution.