There is a marked difference between the rate at which mammals (including us) age and the rate at which many species of reptiles and amphibians age. According to one scientist, this discrepancy may be related to the dominance of dinosaurs during a critical period in mammal history, millions of years ago. Microbiologist João Pedro de Magalhãoes of the University of Birmingham in the United Kingdom describes the “longevity bottleneck” hypothesis in a recently published paper.

There’s this idea: When dinosaurs ruled the Earth, much smaller mammals needed to be able to reproduce quickly to survive; This means that longer-lived genes may have been discarded during the evolution process.

“Some of the earliest mammals were forced to live at the bottom of the food chain and probably spent 100 million years during the period when dinosaurs evolved to survive through rapid reproduction,” de Magalliance says. “I hypothesize that this long period of evolutionary pressure affected the way we humans age.”

The published study states that our very ancient eutherian mammal ancestors must have lost some enzymes during the time of the dinosaurs; These enzymes are enzymes that repair damage caused by ultraviolet light. Interestingly, even marsupials and monocotyledonous plants lack at least one of three UV-reducing enzymes known as photolyases. It’s hard to say whether this is due to their relatively short lifespan.

One possibility is that this loss occurred because mammals became more nocturnal to stay safe, and over millions of years we compensated for this with sunscreen. This is an example of a repair and restoration mechanism that we would otherwise have.

There are other signs too. Take teeth, for example: Some reptiles, including crocodiles, can develop teeth throughout their lives. Apparently people can’t do this; Again, perhaps this is the result of genetic selection going back hundreds of thousands of years.

“We see truly remarkable examples of repair and regeneration in the animal world,” de Magallans says. “This genetic information would have been unnecessary for early mammals that were lucky enough not to be T. rex’s food.”

Of course, many mammals, including whales and us humans, celebrate triple-digit birthdays. Whether we do this because of constraints imposed by our short-lived ancestors or because we have somehow evolved to be impervious to them may be a target for future research. A better understanding of the factors of aging is always useful in combating age-related diseases such as dementia and stroke, and the genetics behind the “longevity bottleneck” can teach us more here.

“Although this is currently only a hypothesis, there are many intriguing perspectives, including the possibility that cancer is more common in mammals than other species due to the rapid aging process,” de Magallians says.