Shining light on dark selection in healthy human tissues.

The genomes of cells across human tissues are riddled by changes to their DNA1–3. Many of these mutations do not alter the properties of a cell, and are neutral passengers. However, a small proportion can change a cell’s fitness, and increase or decrease the progeny that originate from the mutated cell4. How many of these alterations under positive selection (drivers) exist in total is unknown. Whether the current list of drivers is almost complete, or whether large proportions of positively selected drivers in the human genome remain undetected is yet to be determined.