by All human beings age. It is part of our biology and limits our lifespan to just over 120 years.
Not all animals age during their lifetime. Some animals’ bodies do not gradually deteriorate with age as our bodies do.
But when they reach the age of 30, the chance of dying increases by about eight years. So, even if you are lucky enough to be a centenarian, you will have a high chance of dying every year.
This high mortality reflects many other health problems, such as loss of muscle mass and general weakness, cognitive decline, vision and hearing loss and many other degenerative changes that characterize the human aging process.
And perhaps the reason people age so dramatically is that our ancestors changed during the time of the dinosaurs.
Compared to other mammals, humans have long lives. We have the longest lifespan of all mammals on earth, and of all mammals we are probably second only to whales. I say “probably” because you have to keep animals in captivity to study their life cycle in detail, which is almost impossible for whales due to their size and longevity.
We know that species of whales and dolphins show menopause, and all mammals show some form of reproductive decline with age. In fact, all mammals that have been studied show physiological aging and increased mortality with age, even if some species – such as mice and voles – age much faster than others – such as humans, whales and elephants.
But many species of reptiles, amphibians and fish show no signs of aging. Examples include turtles and tortoises, salamanders and rockfish.
One study of 77 species of reptiles and amphibians published in Science in 2022 showed that many species of reptiles and amphibians do not see increases in age-related mortality. It’s as if these animals never age at all. Some of these animals, like turtles, probably live longer than humans.
Perhaps if we study these non-aging species long enough they will show signs of aging. But good luck studying animals like the Greenland shark, which is estimated to live almost 400 years.
At present we can say that, at least among reptiles, amphibians and fish, some species not only live longer than the longest-lived mammals, but age much more slowly. In addition, some of these non-aging species grow throughout their lives, meaning that older females lay more eggs, again in stark contrast to what happens in mammals.
These animals die mainly from being eaten by predators and disease. In fact, most wild animals do not die of old age and, until the 20th century, of course, most people died of infectious diseases.
Some reptiles, amphibians and fish are also known for their ability to regenerate tissue.
Pressure on mammals
Amphibians evolved from fish about 370 million years ago, and about 50 million years later reptiles evolved from amphibians. Mammals then evolved from reptiles about 250-300 million years ago.
We are all products of evolution, which we see in vestiges like our tailbone. Our evolutionary history can have a profound impact on the present day. For example, humans retain evolutionary traits from the time our ancestors roamed the Savannah that are no longer suitable for modern life, from sugar cravings to behaviors that lead to prejudices.
Around 200 million years ago, massive volcanic eruptions wiped out 76% of marine and terrestrial species. After that, the dinosaurs were the biggest predators on earth. To survive and avoid being hunted by dinosaurs, mammals became small, nocturnal and short-lived.
Our modern ancestors were not like us at all. They were more like voles and mice, small animals that go out in the dark to catch insects. Under pressure from the dinosaurs, ancient mammals had to reproduce quickly, just as mice and rats do now. And just like mice, rats and voles, our ancestors had a short lifespan.
For 100 million years, during the time of the dinosaurs, mammals were at or near the bottom of the food chain. Prey mammals were more frequent than predators. During this time there was no reason for mammals to retain processes and genes associated with longevity, such as DNA repair and tissue regeneration systems.
My scrog longevity hypothesis suggests that repair and regeneration systems were lost, mutated or deactivated by the evolution of early mammals. This imposed biological constraints that shape the age of mammals to this day.
After the dinosaurs disappeared when an asteroid hit the Earth 66 million years ago, mammals conquered the earth. An amazing diversity of species has evolved with different life cycles. Some species, like humans, have evolved long lifespans, but they may have done so under constraints, a holdover from the time of the dinosaurs.
Why dinosaurs made a difference
We can guess by looking at species that did not undergo the same evolutionary pressures as early mammals. For example, the tuatara, a reptile endemic to New Zealand, may have looked like a lizard, but it escaped from snakes and lizards around 250 million years ago. It is sometimes referred to as a “living fossil”, because of its slow evolution.
Tuataras are estimated to live for more than 100 years and age much slower than humans, as a DNA analysis study showed in 2022. They may have retained their anti-aging genes, unlike most mammals. even longer lasting.
Our lifespan may be limited due to our evolutionary history.
This article from The Conversation is republished under a Creative Commons license. Read the original article.
Joao Pedro de Magalhaes receives funding from the Wellcome Trust, Longevity Impetus Grants, LongeCity, and the Biotechnology and Biological Sciences Research Council.
