Aging options: a slice of the evolutionary tree
Getting old does not mean getting fat
Biologists have described organisms that do not age with agePavel Kotlyar, Newspaper.
Getting old is not necessarily becoming decrepit and waiting for the last breath. Scientists have found animals that only get stronger with age and can be considered immortal.
While we are young, we are strong and healthy. As we age, we lose strength, health, and the ability to reproduce and die. This is how we usually talk about old age. However, other living organisms inhabiting our planet may age differently, and in their life, old age may not mean weakness, inability to reproduce and death at all.
Therefore, it is high time to redefine the concept of old age in biology, and the aging of the body with age is not a law of nature at all, scientists from the University of Southern Denmark have concluded.
"Many people, including scientists, used to think that aging is something inevitable and it overtakes all organisms on Earth, as it happens to humans: each species becomes weaker with age and dies. However, this is not the case," says the author of the study, Professor Owen Jones.
In their study published in the journal Nature (Jones et al., Diversity of aging across the tree of life), biologists studied 46 different species of plants and animals, for each building a dependence on the age of the two most important parameters for determining old age – the ability to reproduce and the probability of death. This sample included completely diverse organisms: 11 species of mammals (including humans), 12 other vertebrates, 11 invertebrates, 12 plants and one type of algae.
Previously, trying to explain the phenomenon of aging, scientists believed that living organisms maintain their working capacity until they have time to produce and leave offspring. Reasoning like this, we should expect that all animals should become decrepit by the end of fertility. In the case of humans, this is only partially observed. According to a Danish study, the probability of death of modern Japanese women begins to grow slightly immediately after birth. However, many years after the fertile period, women nurse grandchildren and the probability of death remains quite low. And only at a very old age, mortality is rapidly increasing. For example, for the same Japanese women at the age of one hundred years, the probability of death increases by 20 times.
This phenomenon knocks people out of all other animal species that do not have such a jump in mortality at any age: as a rule, this indicator does not increase more than five times in a lifetime.
For most species, mortality does increase with age. This is typical of many mammals, including humans and killer whales, as well as invertebrates, such as water fleas. However, two groups of organisms stand out from the existing theories of aging. One, firstly, includes those who have the probability of dying remains constant throughout their lives, for example, hermit crab and ordinary hydra. Their organisms are not susceptible to senility, which can be interpreted as immunity to aging. Under laboratory conditions, the hydra has such a low chance of dying that it can be considered immortal. "Extrapolating from laboratory data, we can assume that even after 1400 years, 5% of the hydra population can remain alive," Jones explained.
There are also many species of organisms whose mortality rate is almost independent of age. These include rhododendrons, great tits, viviparous lizards, white-necked flycatchers, viburnum forked, finger-dissected kelp, Haliotis rufescens mollusks and red-legged frog.
However, there are organisms whose probability of dying decreases over the years. These include Paramuricea clavat corals, Mexican oaks, and Gopherus agassizii land turtles. Despite the fact that their risk of dying never drops to zero, in old age these animals are more likely to celebrate their next birthday than in their youth.
The constructed dependence of fertility on the age of different species turned out to be no less diverse. In humans, the age of the ability to reproduce is quite short, however, both before and after this period, people live for many years. A similar pattern is observed in animals such as killer whales, chimpanzees, chamois and sparrowhawks. There are also species that only become more prolific with age. An example is the agave plant. On the contrary, in free-living nematodes (roundworms), the ability to reproduce begins from birth, in fact, their life begins from reproduction itself, and fertility decreases with age.
"Surprisingly, we can't even imagine an organism with a life cycle that doesn't exist in nature," Owen Jones is sure. "It is not necessary to treat aging based on how long the body lives. On the contrary, it is much more interesting to determine age based on the risk of death: at what age it grows, and at what age it falls," he believes. According to scientists, the data obtained will help biologists to take a different look at the aging processes of the human body.
Portal "Eternal youth" http://vechnayamolodost.ru09.12.2013