Things that Yoram knows: when and why did we give up immortality?

Eleanor wonders: It seems as if life expectancy was distributed to the animals completely arbitrarily. Why do dogs and cats live so little time compared to turtles or elephants?

"Death at the right time" advises the philosopher Friedrich Nietzsche, and for those who find it difficult to find this time, he explains: "Those who have a goal and an heir, will not want death at the right time for them, for the goal and for the heir. And out of respect for a target and an heir, he will no longer decorate the temple of life with withered flowers." The animals definitely have a purpose and heirs, evolution has designed every living thing so that it will be good to pass its genes to the next generation, for that it must also die at the right time.

Living long is an expensive business. Every living being receives a heavy dose of radiation and toxins from the environment and adds self-made toxins to that: the products of the respiratory mechanism in the living cell. The accumulation of damage from these substances ultimately causes damage to the cell, the cell tissue, the organ and the entire body. A significant part of our gardens deal with the work of cleaning and removing these toxins and repairing the damage caused by them. But evolution does not choose the cleanest and most orderly, but the most efficient in reproduction. Even if we clean every harmful molecule from every cell in the body, there is still a chance that we will die in the teeth of a predatory animal, in an illness or in an accident. The greater the chance, the more questionable the benefit of damage repair mechanisms. The gardens will survive better if the resources are directed not to repair and cleaning but to create a new young and clean offspring. Another motivation to choose a short life is the ability of the species to develop and change. As the animal lives longer, there is less turnover of generations, and therefore also less chance of changes that will allow adaptation to new environmental conditions. For example, the short life cycle of insects allows for the development of resistance to pesticides - the more generations change in a short period of time, the greater the chance that someone carrying a resistant mutation will be found in the crowd.

Indeed, the more an animal is threatened by predators, the shorter its life span and it adapts a strategy of early sexual maturation, short pregnancy, plenty of offspring that quickly reach independence. Thus, the rodents that are easy prey mature quickly and die young. Their relative the porcupine, which has grown effective defensive spines, can afford the luxury of old age and may celebrate its 20th birthday. In a broad comparative study of many species of repulsive reptiles and fish, it was found that the venomous live longer in captivity than their non-venomous relatives of a similar size: those who are more likely to be preyed upon make no effort to extend days

Mammals live longer

 Mammals, as a rule, are not designed for a particularly long life: the female is born with a stock of eggs that does not renew itself, so there is no evolutionary advantage to extending life beyond the age of childbearing. In addition, the teeth do not regenerate like in fish or reptiles, the cartilage wears out and therefore the joints lose flexibility with age and many degenerative diseases afflict them in old age. The cold-blooded ones from whom we evolved, live longer and do not age: a hundred-year-old turtle is still fertile and there are no noticeable differences in the physical fitness of old reptilians and reptiles compared to young ones. Warm-blooded people live with greater intensity, much more food needs to be burned to maintain body temperature, therefore wear and tear is also accelerated.

And now, Eleanor, we finally come to the dogs and cats. The first mammals evolved from the long-lived reptiles about 200 million years ago, but for a very long time they were small and persecuted creatures and accordingly neglected longevity in favor of rapid culture. Only after the dinosaurs disappeared 65 million years ago were some of the mammals able to grow, prosper and some of them embarked on a developmental path in which there is an advantage to longevity. This new longevity is different from that of reptiles and is accompanied by a phenomenon unknown to them: old age. Old age, the result of the evolutionary storms during which the ancestors of dogs and cats lost the ability to repair the accumulated damage over the years, kills the dog at the age of 13. After he had managed to produce several generations of offspring and ensured that there would be someone to shit on the sidewalk even in his absence, the dog gives way to his successors.

The secret of the telomeres

Our life span is limited already in the gardens. The ends of the chromosomes called telomeres shorten with each cell division until they are too short to allow the cell to divide. When cells do not divide, the organs degenerate and death approaches. There are cells where the telomeres do not shorten at all, a special enzyme called, as expected, telomerase takes care of re-lengthening them and thus maintaining the youth of the cell. This enzyme works in fetal cells, but in adults it is only active in those cells that must divide many times: in the bone marrow and in the cells of the immune system. In all other cells it disappears. When there is no telomerase, a cruel hourglass is activated, each cell division shortens the telomere and brings death closer.

It turns out that precisely in mice whose lives are short, the telomere does not shorten in every division and the cell is equipped with telomerase as if it were preparing for eternal life, the rodents reinvented the ability to lengthen telomeres that the first mammals lost. Short and frayed telomeres are found precisely in the Methuselahs among mammals: humans and whales. What is the reason why we choose to activate the self-destruction mechanism and why did we prefer during evolution to forget the repair ability of the telomeres?. A comparative analysis of telomere lengths and the activity of the telomerase enzyme in different animals shows that the silencing of telomerase began at the dawn of the development of mammals from reptiles and is probably related to an important characteristic that distinguishes them from their ancestors: the constant body temperature. Maintaining body heat allowed mammals to operate at night and in cold conditions at the cost of a high consumption of food and oxygen. More oxygen also means more damage to the cell and the genetic material. Mammals are vulnerable, much more susceptible to cancer and have developed defense mechanisms accordingly. In order for a cell to produce a malignant tumor, it must renew the telomeres in every division (otherwise the tumor will degenerate within a limited number of cell divisions). Indeed, cancer cells renew their youth and the telomerase enzyme is active in them just as if they were fetal cells. A cell that can divide forever is a potentially cancerous cell. The longer an animal lives, the more it is exposed to radiation and carcinogenic substances and accordingly the telomerase is less active and the telomeres are initially shorter so that every cell carries a defense mechanism against unrestrained culture. A similar correlation is also found with the size of the animal: a larger body means more cells and therefore more likely that one of them will become malignant and indeed large animals have less active telomerase and shorter telomeres than their smaller relatives. Strengthening of this hypothesis is found in the fact that in the case of birds, long-lived species also have long telomeres and preserve telomerase activity. The birds are better protected from cancer because they have fewer cells and therefore do not require this defense mechanism. In conclusion: paradoxically the self-destruction mechanism embedded in our cells is essential for our health. And like every creature, nature found the right time for us to die.

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More of the topic in Hayadan:

• Towards immortal life
• To immortality and eternal youth
• How many dog ​​years equals a human year? Explanation of calculating the age of dogs

And you can't do without the immortal song Hai Adam Lyrics - Dan Almagor, composed by Bnei Berman, which explains how all animals contributed to man so that he would suffer less. And of course the role of God is played by evolution.