Why do we age and die?

In the marine world, some species of creatures have strange and wonderful abilities that humans cannot possess. For example, the immortal jellyfish - Turritopsis nutricula, the only known case of a multicellular organism capable of turning back the life cycle from adulthood to unicellular. Or Hydra magnipapillata, an invertebrate that can regenerate. When the Hydra is cut into several pieces, each fragment will regrow into a complete new individual.

Their regenerative properties have attracted the interest of biologists in the search for evidence of immortality in the natural world. Why do these species seem to have infinite life, are they completely unlimited like other species?

Hydra magnipapillata, a regenerative invertebrate.

It should be noted that the concept of immortality mentioned in the article is biological immortality. Biological immortality means we're talking about aging. The activities that take place in an organism cannot be senescent or malfunction due to old age. However, they can still die from accident, physical impact, lack of nutrition, etc., etc.

The concept of aging was described in the mid-20th century as a trade-off in cell reproduction and maintenance. Initially, the organism's body uses resources and focus to grow and keep the body healthy. Through childhood and adolescence, the focus is on making the organism as healthy as possible. Once the sex organs are fully developed, that preference gradually shifts to reproduction. Most of the creatures, the resources in the body are limited, putting resources into having children, maintaining the species has to pay with their health.

The salmon swim upstream to lay eggs.

Like a salmon swimming upstream to lay eggs can die soon after. Everything seems to be used just to create the best chance for the salmon to reach spawning grounds. It is rare to make a trip back downstream, survive another year at sea, and return upstream to spawn again. That's too far-fetched and natural selection won't usually favor it. In most cases, this success happens only once in their lifetime.

When organisms reach a sexually appropriate age, aging takes place, eventually leading to death. It's not necessarily about making room for the next generation, says Alexei Maklakov, professor of evolutionary biology and gerontology at the University of East Anglia in the UK. Throughout life, human genes always collect mutations, some completely random, others the result of diet and other external factors. Most of these mutations have no effect or are very harmful to the body.

Gabriella Kountourides, an evolutionary biologist at the University of Oxford, said: "Any genetic mutation that reduces fertility or harms the life of an organism before it reproduces, will be combated. However, when sexual maturity is reached, the point at which an organism can pass on its genes to the next generation, the capacity to resist natural selection also becomes should be weaker".

When swimming upstream to spawn, the trout have done a pretty good job of maturing to reproductive age.

Take, for example, the case of salmon swimming upstream to spawn. The animal has quite well completed maturation to reproductive age. If there is a genetic mutation in the animal that makes it strong after birth and can live for another year, those fish will not have a significant advantage over other fish.

From the point of view of natural selection, there is little benefit to continuing efforts to stay healthy after breeding. 'An individual wants to survive, but at that point, natural selection won't work that hard, because there's no benefit to be had to give to the next generation'.

However, not all creatures are as extreme as salmon. Some species can go on to have more offspring throughout their lives, for example humans. Most mutations to human DNA will either have a negative effect or have no effect at all. Our bodies can repair some of this DNA damage, but that ability diminishes with age.

"Later, senescent cells can accumulate in fish tissues, causing damage and inflammation, and are precursors to age-related diseases. After that, old age and death follow. The first is the accumulation of negative mutations due to weak selection and mutations that can benefit reproduction but harm long-term life." One example is mutations in the BRCA gene, which is known to significantly increase the risk of breast and ovarian cancer. But it's also been linked to high fertility in carriers of this mutation.

Each time a cell divides, the chromosomes lose a small amount of telomere DNA.

The second is cellular senescence, a phenomenon when cells have limited ability to divide. In mammals, chromosomes have protective ends. In humans, telomere repeats range from 5000 to 15,000 bases. Each time a cell divides, the chromosomes lose a small amount of telomere DNA, ranging from 50 to 100 bases. Eventually, when the telomeres die, the cells can no longer divide. They age and accumulate in tissues, causing damage and inflammation, and are also a precursor to age-related diseases.

Although most species age over time, there are some exceptions. For example, many plants have shown 'negligible aging', some species are known to have lived for thousands of years. As is the case with the pando tree in the Fishlake National Forest in Utah. It covers an area of ​​more than 400,000 square meters, and weighs more than 6000 tons. Estimates suggest that this tree population may have lived to be over 10,000 years old.

Or like the immortal snail, a species of the aquatic class with 2 stages of development in the life cycle: the polyp (hydroid) stage and the jellyfish stage. Accordingly, adult jellyfish can reverse the life cycle from adult to polyp if injured, diseased or threatened.