Fruit flies with a 24-hour body clock survive better

Many animals, including people, have a body clock^*1 in the brain. This clock makes the rhythm^*2 of sleeping and waking up. The correct rhythm is about 24 hours, the same as one turn of the Earth. But until now, scientists had not clearly shown in experiments^*3 that this 24-hour rhythm is really important for staying alive.

Now a research group at Okayama University, a university in western Japan, has shown it. The group includes Sae Aikawa, a graduate student^*4, Professor Taishi Yoshii, who studies body clocks, and Professor Makiko Mimura, who studies ecology^*5. Their study was published^*6 in iScience, an American science magazine, on August 10, 2026.

The scientists used fruit flies^*7. Fruit flies are useful because scientists can change their genes^*8 easily. The group made "abnormal^*9" flies. In these flies, only the body clock in the brain was broken. Then they kept the abnormal flies and normal flies together for many generations^*10. The flies had to compete^*11 to survive^*12.

The result was clear. Flies with the correct rhythm had a very big advantage^*13 over flies with a broken rhythm. Flies with an 18-hour "day" became fewer and fewer over the generations. The study shows strictly that the correct rhythm is important for survival^*14.

The study may be important for people, too. Human body clocks are different from person to person. Some people are "morning people" and some are "night people." When a person's own rhythm does not match the time of school or work, this mismatch^*15 may have bad effects on the body and on daily life that we cannot see.

1. *1 body clock: a system inside the body that tells it when to sleep and when to wake up
2. *2 rhythm: a pattern that repeats again and again at the same times
3. *3 experiments: tests that scientists do to find out if something is true
4. *4 graduate student: a student who has finished university and is studying more to become a scientist
5. *5 ecology: the study of how living things live together in nature
6. *6 published: printed or put out so that people can read it
7. *7 fruit flies: very small flies that scientists often use in studies
8. *8 genes: the parts inside a living thing that carry information from parents to children
9. *9 abnormal: not normal; different from the usual way
10. *10 generations: the parents, then their children, then their children's children, and so on
11. *11 compete: to try to win against others
12. *12 survive: to stay alive
13. *13 advantage: something that helps you do better than others
14. *14 survival: staying alive
15. *15 mismatch: when two things do not fit together well