Researchers from Tel Aviv University and University College London believe they have successfully traced the origins of humans diurnal lifestyle, and can explain why mammals tend to sleep at night.
Though most mammals have been going to sleep at night and waking up in the morning for hundreds of thousands of years, that was not always the case. Early species were first nocturnal, and then slowly became diurnal. Though nobody knows why this change occurred, the team in the study believes it is linked to the dinosaurs.
The first mammals evolved long before dinosaurs died off. However, the beasts likely had a large influence on the smaller creatures. As they were constantly under threat from being eaten, it would make sense that the first mammals hid during the day and only came out at night.
“We were very surprised to find such close correlation between the disappearance of dinosaurs and the beginning of daytime activity in mammals, but we found the same result unanimously using several alternative analyses,” said study co-author Roi Maor, a Ph.D. student at Tel Aviv University and University College London, in a statement.
In the study, the team used computer algorithms to look at 2,415 modern animal species and identify how they acted millions of years ago. By focusing on two different mammal family trees, researchers discovered that nearly all early species became active during the day shortly after the dinosaurs died off.
First, the species transitioned to activities that took place during both day and night. After a few millions of years, they completely made the transition.
The research also showed the mammals who would eventually turn into simian primates — a group that includes monkeys and apes — were the first to wake up during the day. That would help explain why simians have excellent day vision compared to other mammals.
However, while the study present compelling evidence, the team states that they cannot assume the fall of the dinosaurs directly led to the shift in sleeping patterns. It is likely, but more research needs to be done before such claims can be made.
“It’s very difficult to relate behavior changes in mammals that lived so long ago to ecological conditions at the time, so we can’t say that the dinosaurs dying out caused mammals to start being active in the daytime,” said study co-author Kate Jones, a researcher at University College London, according to Newsweek “However, we see a clear correlation in our findings.”
This research is published in the journal Nature Ecology & Evolution.