Human earwax, whether removed by a curious finger or an ill-advised cotton swab, is usually tossed in the nearest garbage shortly after its removal. But this sticky substance can hang on to clues about health that build up in the ear canal over time—including in the giant ears of whales.

Luckily, museum curators around the world have had the good sense to hold onto massive plugs of earwax pulled from dead whales over the centuries.

Thanks to those plugs, scientists have now discovered a record, hidden in earwax, of how human activities have stressed out whales over the past century and a half. Stephen Trumble, a comparative physiologist at Baylor University, and his colleagues published the findings this month