When will life end

Death and evolution : "Eternal life would be possible, but not very useful"

93 percent of the people who have been born so far are dead. The remaining 7 percent are still alive. But we too will die. It is so certain that it seems banal. And yet biologists are concerned about it. Why?

Because death cannot be taken for granted. At least if you look at the whole diversity of nature.

Explain, please. All living things die at some point.

No, not necessarily. A sponge that researchers discovered in Antarctica has lived for 10,000 years. Single-cell organisms like the paramecium even have the theoretical chance of living billions of years because they keep dividing. Many living things are potentially immortal.

What does that mean? Are such organisms mortal or not?

Scientists put it this way because these living beings are naturally also threatened by so-called “extrinsic mortality factors”, i.e. can be destroyed by external forces. For example, if the water in which the paramecium lives dries up, it dies. If tremendous physical forces pull the sponge during turbulence, its life can end. The longer the potentially immortal living beings exist, the more likely it is that catastrophic death will occur at some point. But their life processes always remain stable, they do not die of their own accord.

And is that different with humans?

The human organism is such that, after a certain number of years, it destroys itself, as it were. The body cells follow an internal program. It is an extremely complex process in which the chemical activity changes, repair mechanisms are used less and less, and new cells are created less and less through cell division. Some genes that are useful to us at a young age begin to be destructive. We age until we finally die, at the latest at a little over 120 years.

Why is there this built-in "suicide program" at all? Doesn't the principle of “survival of the fittest” apply in nature? In fact, evolution should always favor those who live particularly long.

Nature does not only favor a long life. But above all the ability to cope with life's challenges. A good immune system, for example, is helpful for this. That in turn costs a lot of energy, so much that an organism can only muster it at a young age, but not in the long term. Because, again: every living being is constantly threatened by catastrophic death. It is therefore extremely important that organisms function optimally at a young age so that they can reproduce their own genes as best as possible by reproducing.

But why does death follow from this?

Because resources are limited, optimizing the young life comes at the expense of the older life. Gradually there are fewer and fewer options available - for example, to have an excellent immune system. The result: the aging process gets going until the organism finally dies.

Then why don't people die immediately as soon as the offspring are viable? They live on for a long time, although their children have long since ceased to depend on them.

This is a problem that evolutionists have puzzled over for a long time. With men it seems easy, they can still father new children well into old age. It is different with women, after menopause they can no longer bear children; they become sterile. And yet they live on for a long time. Biologists now explain this with the "grandmother hypothesis".

What does this mean?

Women play a major role in ensuring that their grandchildren also grow up healthy. If the mothers were alone with their children, they would simply be overwhelmed. Especially when the offspring are of different ages. The younger ones need the care of their mother, the older ones are taken care of by the grandmother. Long-term studies show that children are more likely to survive when grandmothers are part of the family, at least grandmas on the side of the mothers. So it makes perfect sense that nature has established a lifespan even after fertility has ended.

But isn't long human life expectancy a victory for medical progress? Without the possibilities of medicine, wouldn't people die much sooner, perhaps once they have raised offspring?

Medicine is helping more and more people to live longer, that's true. But this has not yet changed anything in terms of the genetic programming of the cells. Remember: In relation to the tribal history of our species, medicine is still very young. People without modern medical care carry the same genetic death program in their cells. Once they have overcome the risk of dying in infancy or childhood, they can live long - but eventually age and die.

So is the sentence attributed to Goethe correct: "Death is nature's contrivance to have a lot of life?"

Yes, that is aptly expressed, whereby a second aspect is addressed here. Change would not be possible without death.

This is exactly what sex is for: when the genes of women and men unite, a new variant of the genetic material arises and with it the possibility that life adapts better to the conditions of the environment.

That's the way it is. From an evolutionary point of view, the inner program of mortality and bisexual sexuality are closely related. Because both serve the same purpose. Namely the best possible self-preservation and reproduction under constantly changing living conditions. Researchers often simulate the evolutionary process on the computer. The simulations show: Actually there could be immortality, but this way of life would be evolutionarily inferior to the way of life with sex and death, at least in the case of “higher” organisms.

That sounds very strange.

Because it is important to us to live long. But evolution doesn't care about the fulfillment of our personal wishes.

Eckart Voland (63) is Professor of Biophilosophy at the Justus Liebig University in Giessen. He is currently a Fellow at the Alfried Krupp Science College in Greifswald.

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