Why Aging can be Avoided

Why Aging Isn’t Inevitable Excerpt from the book "Cracking the Aging Code"

(Cracking the Aging Code:
The New Science of Growing Old-And What It Means for Staying Young)

Translated by Vyacheslav Golovanov, GeekTimes

Humans age gradually, but some animals begin to age very quickly at the end of life, while others do not age at all, and some may even get younger. The variety of aging mechanisms in nature should alert lovers of generalizations – especially against generalizing the inevitability of aging.

Bacteria reproduce by dividing symmetrically in two. What can aging mean for bacteria that have no difference between parent and child after division? Unicellular protists like amoebas also reproduce symmetrically, but they still invented a way to age. And even among macroscopic life forms, life expectancy varies enormously depending on the local ecology and the rate of reproduction. It is unlikely that this could happen as a result of a universal and unshakable process; such a subtle adjustment clearly indicates adaptation.

Life expectancy varies from Methuselah to genetic kamikazes dying by spring noon. Dragonflies live for four months, adult one-day flies live for half an hour. We live for about 70 years, and the ginkgo meristem can be millions of years old. This diversity is even more impressive if we remember that the genetic basis of aging is common to many creatures, from yeast to whales. But somehow the same genetic mechanisms inherited from common ancestors at the dawn of life were changed to create very different lifespans, from hours (yeast) to thousands of years (sequoia and aspen poplar).

Mayflies die quickly and suddenly at the end of their reproductive cycle

Not only the life expectancy varies greatly, but also the pattern of withering during this period. Aging can occur gradually throughout life (lizards, birds), or the body may not age at all for decades, and then suddenly die (cicadas, agave).

Our inner killer works quietly, like an evil empress poisoning her husband; but in other creatures, inner killers work faster, and in some there are no genetic programs of death at all. Such diversity is an unambiguous signal of a feature formed by natural selection, and not the inevitable law of entropy.

Since the biomarkers of aging vary so much in different creatures – and even in different representatives of the same species – it is very difficult to derive a universal definition. A person can prematurely turn gray, a naked baby blind can be covered with wrinkles. For an actuary, the answer to the question is simple, even if only statisticians like the answer: aging is an increase in the mortality rate. In other words, in the process of growing up, the risk of death of the animal increases.

For example, a 20-year-old has a 99.9 chance of living to the age of 21. That is, his chances of dying are 1 in 1000 per year. If this continued, then a 40-year-old would also have a 1 in 1000 chance of dying before his 41st birthday. And we would call this situation "lack of aging". In reality, a 40-year-old already has 2 chances per 1000 to die before his 41st birthday. Doubling the risk of death in 20 years is proof of gradual aging.

Further - worse. A 60-year-old has a 10 out of 1000 risk of dying, an 80–year-old has 60 out of 1000.

Probability of death depending on age

The risk of death is not just increasing, but increasing with acceleration. The increase in wear and tear, or the chances of dying every year, as it happens to us after reaching adulthood, is called "accelerating decrepitude." But other creatures have different patterns. The probability of death may increase, and then level out: "slowing senility", or even a "plateau of mortality". If we choose this definition of aging, we will have to say that if the probability of death does not increase, then the species does not age. Continuing the trend, although it sounds strange, we can say that if the probability of death decreases with age, then the species ages on the contrary, which is called "negative decrepitude".

There is another objective measure of aging – a decrease in fertility. Just as mortality is determined by the probability of death, fertility is determined by the probability of reproduction. Men gradually lose fertility with age. In women, this happens faster, and drops to zero at the time of menopause. But other species have other patterns and schedules. For some, fertility has been growing for most of their lives – another variant of "negative decrepitude".

For example, the Blanding turtle, living in the American Midwest, gradually ages for several decades, and does not grow, but at the same time increases fertility. Obviously, her risk of death decreases with age. From the point of view of evolution, the loss of fertility is the main sign. From the point of view of natural selection, after the loss of fertility, you are already as good as dead.

It is natural for us to classify different species by life expectancy, lump together insects that live for one day, and separate them from trees and whales that live for hundreds of years. But most of these differences can be attributed to size. Everything from growth and fertility to aging should happen more slowly in hippos, with a slow metabolism and tons of flesh. Therefore, we are more impressed by a bee living for 20 years than a moose living for 20 years.

But what if we stop looking at life expectancy and compare different species based on shape rather than the length of their lifeline? Whether their life is long or short, we will display it on the same scale for comparison. Don't ask how long they live, ask if the population is dying gradually, or if many of them die in infancy, and then mortality decreases, or if all deaths occur near the end of the life cycle. The graph published in a paper from the journal Nature in 2014 is built exactly like this, and the range of nature's ingenuity is very clearly visible on it. All possible combinations are presented, with rapid aging, without aging, with reverse aging, and at the same time they can be combined with life cycles of weeks, years or centuries. At the same time, the neighborhood on the charts is completely unexpected. For example, at the top of the graph, with a small mortality rate that suddenly rises towards the end of life, there are people, laboratory worms and tropical fish. From the point of view of the laws of aging, people are more like laboratory worms than chimpanzees.

The dark line is fertility, the light line is survival. human; guppy; chimpanzee; 
laboratory worm;
oak; turtle; pyrenean dioscorea; lizard;
hydra; hermit crab; vole mouse; viburnum

The graphs show the variety of ways in which animals and plants age in the wild. The light, downward–sloping line is the survival curve, and the fat curve below it is fertility. The downward slope of the survival curve means that fewer and fewer members of the species remain alive over time. The graphs are constructed in such a way that a straight line going down diagonally will be neutral – that is, it means no aging. Lines with a hump above the diagonal mean normal aging, and lines with a deflection at the bottom mean reverse aging, or "negative decrepitude". For example, people's line remains flat for a long time, and then falls quickly. This means that many people live for a long time, and then their deaths are grouped at the age of 80-90 years (statistics taken from modern Japan).

But in animals and plants in the bottom two rows, mortality is more evenly aligned. In turtles and oaks, the curves have a reverse bend. This means that they die less often in old age than in youth – this is reverse aging.

The bold line, fertility, is quite clear. Fertility may increase with the growth of an animal or plant, or decrease with reproductive age – for example, in menopause. Note that animals from the top row lose their fertility long before death. This is an evolutionary paradox.

In this diagram, if the survival curve looks like a straight diagonal, it means there is no aging – for example, like in hydra and hermit crab. Hydra is something like a freshwater jellyfish, several millimeters long, and it is found in ponds. All animals from the top row demonstrate "real aging" – the probability of death increases with age. The next two rows represent plants and animals that do not age, or age the other way around. The older they are, the lower the risk of death. This is true for most trees, and for turtles, as well as for oysters and sharks (which are not represented here).

The fat curve at the bottom is fertility. Animals from the top row finish reproduction long before death. This leads us to the paradox of evolution for orthodox Darwinists: if the sole purpose of natural selection is to maximize reproduction, why did evolution allow reproduction to fall to zero with so many individuals remaining alive? The rise of fertility curves means an increase in reproduction with age, which is another example of negative decrepitude. When a tree gets bigger every year, it is not surprising that it produces more seeds. Dioscorea pyrenaea is a liana growing on rocky cliffs in the Pyrenees. If she is not disturbed, she lives at least 300 years, without signs of aging. At the same time, its fertility in the first 20 years is almost at zero.

The point of the graphs is that nature can do anything with aging. Any timeline, any form is possible, and each species has adapted to its ecological environment in its own way. There are no restrictions.

Instant aging

You can age to death quickly and suddenly, at the end of the reproductive cycle. Sudden death after reproduction is often found in nature in such different organisms as mayflies, octopuses, salmon, not to mention thousands of plants blooming once a year. Biologists call this "semelparity", from the Latin "one birth".

The causes of death of semelparous organisms are extremely different. Octopuses stop eating. Male mantises sacrifice themselves for reproduction, going for a snack to females. Salmon destroys its body by releasing steroids.

By the time an adult salmon reaches the spawning area, its metabolism is already in the pre-collapse stage. The adrenal glands produce steroids (glucocorticosteroids), which lead to accelerated, almost instantaneous, aging. They stop eating. Steroids lead to the collapse of the immune system, their bodies are covered with fungus. The kidneys atrophy, and neighboring cells increase. The circulation system also suffers. Arteries are damaged in a way similar to human heart disease. Swimming upstream is very difficult, but their bodies are not damaged by mechanical impact. A cascade of biochemical changes that occurs immediately after reproduction is responsible for this.

Some organisms are genetically programmed to stop eating after reproduction, and starve to death; this is faster and more reliable than normal aging. Mayflies do not have a mouth and digestive system at all. Elephants chew so many leaves and twigs in their lifetime that they wear out six sets of teeth. But when the sixth set ends, a new one does not grow, and the thick-skinned die of hunger.

Longevity

In 2014, photographer Rachel Susman published a photo album with antiquities, entitled "The oldest living creatures in the World." All these are plants. One of the reasons for this is that plants do not need to worry about leg muscles strong enough to walk. Being tied to one territory, they can grow and grow stronger, become older and more fertile than any animals, and reap the fruits of age.

Plants have another secret of longevity. In the early stages of an animal's life, the germ cell line separates from the rest of the body, or soma. Only the germ line needs to be preserved intact so that it turns into the next generation. The body can afford not to be so careful with soma cells and save on their reproduction. But plants have a different system. The soma and the germ line are not separated. Plants also have stem cells, and their cells are responsible not only for the growth of the plant, but also for the seeds and pollen that will become the next generation. In a tree, stem cells are located in a thin layer under the bark, the meristem. It spreads to all branches and knots, and leaves grow from it, as well as buds and seeds. Some ginkgo, non-flowering trees that originated in the Permian period 270 million years ago, may have a meristem a million years old.

But most trees have a certain age, after which mortality increases every year. Stem shoots begin to grow directly from the trunk, while the growth of branches slows down. There are signs that trees become more vulnerable to fungi and diseases with age, but they are usually destroyed by mechanical stress from excessive size. The very possibility of continued growth, which gives them the property of "reverse aging", leads in the end to their decline.

Aging on the contrary

The medusoid Turritopsis nutricula does not return to kindergarten at the age of 65, but in 2010 he received his 15 minutes of fame when he was called an "immortal jellyfish" in scientific journals. Adult Turritopsis has acquired a clever trick: having generated polyps, he regresses back to the polyp himself, and starts life over again. This is due to the transformation of adult cells back into stem cells, which goes against the usual direction of development, from stem cells to specialized ones. He's driving back down a one-way development street. The headlines referred to Turritopsis as the "Benjamin Button of the Sea."

Skin-eating beetles (Trogoderma glabrum) perform a similar trick, but only when they are starving. Developing on animal carcasses in the forest, they go through six different stages of larvae. At first they look like worms, then like millipedes, then like a water skimmer to finish the development in the form of six-legged beetles. A pair of entomologists from the University of Wisconsin in 1972 isolated beetle larvae at the sixth stage of development (when they were ready to become adults) in test flasks and found that without food they return to the fifth stage. And if they starve for many days, they decrease and return further back in stages until they turn back into larvae, as if they had just been born. If feeding is then resumed, they go forward through the developmental stages, and become adults, maintaining a normal life expectancy. They are able to repeat this cycle over and over again when scientists fatten them up to the sixth stage, and then starve them so that they return to the first. The usual life expectancy of eight weeks thus stretched over two years.

Ancient aging

Hydra are invertebrates with radial symmetry, each with a mouth on a stem surrounded by tentacles that grow if they are cut off – just like the multi-headed monster from Greek mythology, after which they were named. They have been observed for up to 4 consecutive years, starting with specimens of different ages caught in nature, and over time they do not die and do not become more vulnerable to predators or diseases. In the human body, special cells, such as blood, skin and stomach cells, die and grow back. Hydra's whole body is arranged this way, it regenerates from the stem cell base every few days. Some cells die, others, having reached a certain size, turn into hydra clones, which bud off from her body. This is an ancient method of reproduction, coping without sex. For hydra, sex is optional – she rarely does it.

A recent article claims that hydra is aging, and this can be seen by the decrease in the cloning rate. The author believes that it is possible that clones inherit the age of the parent. It is hypothesized that only sexual reproduction resets the aging clock. If so, then hydra aging is a return to protists, hereditary microbes more complex than bacteria. Some of them have a limited life time, because they can divide a limited number of times, after which they run out of reproductive gasoline – unless they are restarted by gene exchange (a version of sex for protists), which restarts their clocks. Amoebas and microbes of the genus Paramecium are examples of such protists, unicellular with a long life line, which in ancient times gave rise to more than 100,000 species – algae, slugs, infusoria, and other organisms that do not belong to the kingdoms of animals, fungi, plants and bacteria.

Disabling aging

Queen bees and worker bees have the same genes, but different lifespans. In queens, royal jelly disables aging. When a new hive begins, the nurse bee chooses - as far as we can tell, by chance – one larva, which will get the liquid royal diet. A certain physiologically active chemical ambrosia in royal jelly switches the lucky bee to growth mode, and it turns into a queen, not a worker bee. The milk gives the queen excessively developed sex glands, which is why she acquires a characteristic size and shape. The queen makes one flight at the beginning of her career, during which she can mate with a dozen different drones, and store their sperm for years.

Under the weight of the eggs, the adult queen can no longer fly, and becomes a reproduction machine. She lays 2,000 eggs a day, more than her own weight. Of course, such a machine requires a retinue of workers serving it to feed, remove waste and transmit pheromones (chemical signals) to the rest of the inhabitants of the hive.

Worker bees live for several weeks and die of old age. And they don't just wear out from the affected body parts that break down in the cruel world where they live. Their survival follows a familiar mathematical form, the Gompertz curve — a characteristic survival graph typical of humans and other animals, indicating aging. But queen bees, although their genes are identical to worker bees, do not show symptoms of aging. They can live for years, and sometimes, in stable hives, for decades. They represent miracles without age. The queen dies when she runs out of sperm obtained during the wedding flight. She can continue to lay eggs, but they will be unfertilized and only drones without stings can grow out of them. The same workers who served the queen are killing her by surrounding her and pinching her to death.

Life expectancy after the reproductive period

Why does menopause exist? We take care of young and large families, and our devotion does not end after the children grow up and become parents themselves. Therefore, the usual explanation of life continuing after the end of fertility is called the "grandmother hypothesis". Women have a genetic interest in raising healthy grandchildren. Perhaps, at the age of 60, they can give more to their genetic heritage by caring for grandchildren than by giving birth to their children. The hypothesis sounds reasonable, at least to humans, but demographic researchers have found it very difficult to confirm with numbers in hand.

Whales and elephants are also experiencing their fertility. They are also social animals. Perhaps they are more important to their grandchildren than we think. But there are other animals that live after their fertility has been exhausted. Guppies, water fleas, nematodes, rotifers, compared to which any idle father looks like Mary Poppins. They lay eggs and that's it. And the wing (or fin) will not move to take care of the young, and even more so – about the grandchildren. And, nevertheless, modern evolutionary theory says that no natural selection forces them to live on, so they must die off.

In 2011, Charles Goodnight and I came up with how evolution could lead to the emergence of life after reproduction. The idea itself sounds unlikely, but it matches the numbers. The old segment of the population, retired, is needed to maintain the stability of the population in cycles of abundance and hunger. In good times, they eat excess food and prevent excessive population growth. When there is not enough food, they die first.

The types of aging in nature are as diverse as possible, which suggests that nature can turn aging on and off at will. Therefore, we can be forgiven for considering with great skepticism the theories that speak of the need for aging. Whatever theory of aging we have, it needs to be flexible, diverse and not reject exceptions.

About the authors:Josh Mitteldorf is a theoretical biologist, PhD at the University of Pennsylvania.
He has his own website AgingAdvice.org , and he writes a blog column ScienceBlog.com . Conducts field classes at MIT, Harvard and Berkeley.Dorion Sagan is a well–known writer, environmental philosopher, and theorist.
His articles have appeared in publications such as Natural History, Smithsonian, Wired, New Scientist and The New York Times.

Portal "Eternal youth" http://vechnayamolodost.ru  16.06.2016