Y Pan

A translator who starts mixing up words with age turns a precise document into nonsense. In the cell, that translator is transfer RNA: it carries amino acids to the ribosome, where protein is assembled. An error in a single "word" can make a protein useless or harmful. Researchers have found that in mammals a rare chemical mark on this RNA, the manQ modification, disappears with age.

On a packed bus, passengers instinctively edge away from the person who has taken up too much space or is acting strangely. Something similar happens in the body's tissues: when a senescent cell, one that has stopped dividing but hasn't died, appears among normal cells, its neighbors begin to crowd it.

In a hall of mirrors, a person walks up to a curved mirror and sees themselves now as a dwarf, now as a giant. Popular machine learning models behave in much the same way when asked to guess biological age from blood tests or brain scans: they stretch age at the extremes, underestimating it in older people and overestimating it in younger ones.