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This article comes from the official account of Wechat: SF Chinese (ID:kexuejiaodian), author: SF

Many mammals, including us, age faster than many reptiles and amphibians. One biologist suggested that part of the reason for this is that the dominance of dinosaurs in the past forced mammals to shorten their reproductive cycles and led to the elimination of some of their anti-aging genes.

The progress of science has given us a deeper understanding of the process of aging. However, why do we grow old? Why does evolution leave us with a body that decays at the age of 80 or so? After all, living longer gives us more opportunities to have offspring, which seems to be in line with the logic of evolution.

There are some long-lived animals in nature, such as bowhead whales and some giant turtles, which can live more than 200 years. In some animals, the physiological mechanism of aging is very slow, and even stops completely in some species. However, humans and most mammals do not have such an advantage-we age faster, we have less ability to regenerate tissue, and we are more likely to develop cancer than reptiles and amphibians. Why did evolution put mammals on a different path?

If you want to live long, you have to pay a certain price. if you want to understand the evolution of longevity, you must first understand that this evolutionary feature of longevity has a price. It takes a lot of energy to maintain and repair DNA, replace damaged cells, and resist other aging processes. For most animals, energy is a hard-won resource that can only be obtained by feeding. This means that when an animal ages more slowly, it has less energy to do other things, including reproduction.

However, if an animal ages slowly and lives to be over 200 years old, but dies in its 20s because of infectious diseases, predators and other reasons, then their longevity genes do not work. In this case, longevity is a disadvantage. Because this creature wastes a lot of energy to inhibit aging, which could have been used to produce more offspring.

Therefore, if an animal has a high chance of dying due to other factors before reaching its natural lifespan, this will exert selective pressure on the animal to accelerate reproduction at the expense of shorter lifespan. This trade-off is common in nature.

One theory about why humans don't live longer is that our mammalian ancestors often die young. So what factors posed such a great threat to our mammalian ancestors that they affected our human lifespan?

Dinosaurs put pressure on mammals. Recently, Jo ã o Pedro de Magalh ã es, a biologist at the University of Birmingham in England, proposed a hypothesis called "longevity bottleneck". He believes that dinosaurs had an important impact on the lifespan of mammals.

Mammals differentiated from reptiles 200 to 250 million years ago. At that time, they were small and nocturnal, coexisting with dinosaurs for more than 100 million years.

Magalhaes suggested that early mammals originally had longevity genes that originally belonged to reptiles. However, during the long years of coexistence with dinosaurs, these genes were gradually eliminated because they did not bring evolutionary advantages in a dangerous environment full of ferocious dinosaurs. As a result, mammals choose to speed up reproduction at the cost of shortening their lifespan. After the extinction of the dinosaurs, some mammals re-evolved a longer lifespan, but were constrained by the loss of reptile longevity genes millions of years ago.

The "longevity bottleneck" hypothesis is not the first to suggest that dinosaurs had a significant impact on our evolution. As early as 1942, Gordon Lynn Voles, a physiologist at the University of California, Berkeley, put forward the "nocturnal bottleneck" hypothesis. He believes that during the reign of dinosaurs, almost all mammals evolved into nocturnal animals. Although some mammals evolved into diurnal animals after the extinction of the dinosaurs, many nocturnal evolutionary characteristics remain in today's mammals. For example, there is genetic evidence that mammals lost photolyase during dinosaur reign, and this enzyme can repair ultraviolet damage to DNA.

Of course, dinosaurs are not the only factor that may affect the rate of aging in mammals. Magalhaes also mentioned the role of body temperature. Mammals are thermostats, which brings an evolutionary advantage that allows them to control their body temperature without relying on environmental conditions. However, there is also some evidence that higher body temperature can lead to shorter life expectancy.

All in all, Magalhaes's hypothesis provides a new perspective for exploring the aging evolution of humans and mammals. And it's interesting to think about it: although mammals have replaced dinosaurs as the masters of the earth, the influence of dinosaurs remains in the DNA of mammals.

References:

Https://onlinelibrary.wiley.com/doi/10.1002/bies.202300098

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