There is a distinct difference between how quickly mammals, including us, age, and how quickly reptiles and amphibians age. Scientists suggest that this difference may be related to the dominance of dinosaurs millions of years ago. Science Alert presents this hypothesis.
The “longevity bottleneck” hypothesis.
João Pedro de Magalhães, a microbiologist at the University of Birmingham, UK, describes the “longevity bottleneck” hypothesis in new research. This hypothesis suggests that when dinosaurs dominated Earth, smaller mammals needed to reproduce quickly to survive, and genes for longer lifespans may have been eliminated as evolution progressed. Mr. de Magalhaes said:
Some of the first mammals were forced to live at the bottom of the food chain, and likely spent 100 million years during the age of dinosaurs evolving to survive through rapid reproduction. I suggest that this long period of evolutionary pressure has an effect. In the way we age as humans.
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Translation: Some of the first mammals were forced to live at the bottom of the food chain, and likely spent the 100 million years of the dinosaur era evolving to survive through rapid reproduction. I think long evolutionary pressure has an impact on the way we humans age.
The new study suggests that our ancient ancestors, the lineage of eutherian mammals, may have lost some enzymes during the age of dinosaurs. These enzymes repair damage caused by UV rays. Interestingly, marsupials and monopods lack at least one of three UV repair enzymes known as photolyases. I don’t know if this has anything to do with the relatively short lifespan.
One possibility is that mammals lost this enzyme when they became nocturnal to be safer, and millions of years later we replenish it with sunscreen. This is an example of the repair and restoration mechanism that we should have had in place originally.
There are other signs as well. For example, teeth. Some reptiles, including crocodiles, can continue to grow teeth throughout their lives. But humans can’t. This may also be the result of genetic selection dating back hundreds of years.
“We see some really amazing examples of repair and regeneration in the animal world,” de Magalhaes says. “Early mammals that weren’t lucky enough to fall prey to tyrannosaurs probably didn’t need this kind of genetic information.” Of course, many mammals, including whales and us humans, live for more than 100 years. Future research might explore whether they do so under constraints imposed by their short-lived ancestors, or whether they have somehow evolved to be immune to constraints.
“Although it is only a hypothesis at this stage, there are many interesting angles, including the prediction that mammals age more quickly and therefore develop cancer more often than other species,” de Magalhaes added. To combat age-related diseases such as dementia and stroke, it is always beneficial to better understand the factors behind aging. And the genetics behind the “longevity bottleneck” may have a lot to tell us here.
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