Kids' thumbs are getting bigger and stronger because they spend so much time texting and playing computer games.
Researchers reckon teenagers use their thumbs more than their fingers these days, which is causing them to change shape.
Young people are even using their thumbs to do things like point or ring doorbells.
Thumbs up
Using thumbs is so common in Japan that teens have been nicknamed the "thumb tribe" and the "thumb generation".
Researchers who did the study noticed that kids who text all the time naturally used their thumbs to type on a keyboard, without even thinking about it.
Most adults don't use their thumbs nearly as often.
Scientists reckon this is proof that modern technology can change the way our bodies grow and develop.
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Comment: can games help you learn?
