There’s one very big reason that we are not nocturnal and can live our lives during the day, and that’s because dinosaurs were killed off by an asteroid many millions of years ago, an extraordinary new study claims. The findings, which were detailed in the journal Nature Ecology & Evolution, indicate that this catastrophic event would be the catalyst for many mammals making the switch from nocturnal to daytime living.

Most mammals were creatures of the night back during the time of the dinosaurs, which scientists attribute to the dinosaurs dominating the daytime. Scientists have found signs that mammal species today used to be nocturnal, as most mammals except humans and other primates don’t have a fovea, which is the area in the retina of the eye that results in better visions, and the eyes’ shape tends to betrays a bias toward low-light sensitivity.

We also have a strong sense of smell and better hearing than if we had developed during the daytime, as we had to survive in the poorer visual environment of night. This would have helped us to avoid interactions with dinosaurs, who did operate during the day. However, the evidence is largely indirect for this, and more research will need to be conducted to confirm these findings.

“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,” explained lead author, PhD student Roi Maor (Tel Aviv University and UCL).