Suppose humanity sent a reconnaissance probe to some distant planet, and it discovered a substance not found on Earth. What should he do with her? Chemical analysis? What if it is alive and chemical analysis will kill it? How to find out?
Now in science there are about a hundred definitions of what life is. And when there are so many definitions, it means that scientists themselves do not fully understand what it is.
Many definitions refer to "proteins" and "cells" that may not necessarily be present in alien life. Moreover, it seems that at the beginning of earthly life they were also absent (but more on that later).
If we try to take the common part from these definitions, it turns out that living things exchange substances with the environment (metabolism), has the ability to grow, react to external conditions, reproduce …
Let's check these provisions.
Metabolism. This is a property of almost any chemical process. The same candle fire, for example, takes oxygen from the environment and gives off carbon dioxide, just like we do. Does that make him alive?
Reproduction. A computer virus also multiplies.
Growth. Crystals grow too. And by knocking over the same candle, you can accidentally "spread" the fire throughout the room.
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Reaction to external conditions. Ice crystals grow faster at low temperatures - they react to external conditions.
This means that all these signs - metabolism, the ability to reproduce and grow, react to the external environment - are not enough.
Scientists have supplemented the definition of life with a new condition: a living being in the process of exchange creates more complex substances.
The crystal grows, the computer virus multiplies, the fire creates complex substances. But this is not life!
On the one hand, the condition is true: the whole set of living proteins (and there are millions of different ones) is created from twenty-odd amino acids. On the other hand, in the same candle flame, very complex substances are created randomly: anthracene, phenanthrene …
There is, however, a fundamental difference.
What is synthesized in a flame is not necessary for fire, even harmful (from soot, for example, it goes out). But what is synthesized in a living organism is used to build it, to help in the same synthesis, to protect it from the external environment. It remains, and then it can go to descendants.
This condition, which was called "accumulation and transmission of information", is now considered the main property of life. And how this information is accumulated - by the synthesis of substances necessary for survival, by the transfer of antibodies, by innate instincts or by the printed word (as it happens to you now) - this is already secondary.
How could the inanimate become alive?
How did life come about? There are many answers to this question too. “Brought from space”, “landed as an experiment by a certain civilization” - such answers only again raise the same questions: how then did life arise on the home planet of this certain civilization?
Observing the living world around us, it is very difficult to imagine that all this complexity and diversity could somehow arise on their own. And if we assume that in some ancient times all living things were represented by only one kind of life?
Now geologists find a multitude of layered stones, stromatolites, which are formed by perennial colonies of cyanobacteria. So, the oldest of these stones are three and a half billion years old. No more traces of the activity of living beings of that time are known. That is, it seems that the only ones who then lived on Earth were cyanobacteria.
Stromatolites.
But even a bacterium is already a very complex organism. Many different proteins are synthesized in it, hereditary information is stored in DNA, and RNA (ribonucleic acid) is used for transmission and transport. Could it be that all these substances suddenly appeared by chance and combined together?
Cyanobacteria.
Scientists have recently discovered that there are biochemical reactions for which protein is not required. These reactions can proceed with the participation of RNA alone, the so-called ribozymes.
Let's imagine such a living organism. It most of all resembles a drop with a solution of nucleic acids inside. Some molecules store hereditary information, while others synthesize new RNAs. Still others form a shell.
How does nutrition and reproduction occur in such an organism? Suitable molecules from the external environment pair with shell molecules and are pulled inward. Internally, they pair up with pre-existing "long" RNA chains in the same way. Naturally, for a new chain to bind by chemical bonds, it takes a very long time, or a short-term high temperature, or the help of another RNA-ribozyme.
RNA molecule under an electron microscope.
But the main task is at the very least fulfilled - such a drop of solution can already accumulate and transmit useful information, that is, it already lives.
What makes the right molecules combine?
Accident?
Language theory of life
So, we found out that life arises as a result of the combination of inanimate elements, and its main feature is the ability to store and transmit information.
And now - attention. There is a phenomenon that behaves in the same way, although we do not consider it alive. True, we often call this phenomenon "living", but in a figurative sense. What is this phenomenon? Take a look at the picture.
Try to read what is written here. Nothing written! They are just letters, and there is no sense in their random accumulation. We can say that this collection of letters is "dead".
And now the same letters are connected in a specific order:
Try to read what is written here. Nothing written! They are just letters, and there is no sense in their random accumulation. We can say that this collection of letters is "dead".
And now the same letters are connected in a specific order:
Have you guessed which phenomenon has the same properties as life? Tongue! The ordinary language in which we speak, think, read and write. And even sometimes we call it "alive":
It accumulates and transmits information, and meaning (life) arises in it as a result of the combination of meaningless (nonliving) elements …
And that is not all! A language is capable of “growing” (the number of words and meanings in it increases), “multiplying” (forming dialects, adverbs, jargons, slangs, literary genres) and creating “complex substances” (human actions).
And finally: many poets and philosophers seriously argue that it is not we who "speak with language", but that language "speaks with us." That is, we do not have a language, but we have a language.
That is, language uses people as a tool and a breeding ground. We pronounce sounds for him and write letters, and the language itself puts thoughts for these words and letters into our heads …
And what if the language used not people, but, for example, molecules as "service personnel"? Although - stop, stop …
He uses them, we just read about it! It is precisely as a result of the use of nitrogenous bases for the formation of words - DNA, that life arose on Earth!.. It turns out that philosophers and poets are right. Language created people.
From living to lifeless and back
For the emergence of life, metabolism and synthesis of substances are necessary. When these processes stop, it is believed that life has also stopped. Is this termination always permanent?
Green frog.
Let's take a regular green frog. They often hibernate in the same place where they live, at the bottom of the pond. When winter comes and the reservoir freezes over, frogs often freeze with it. Their heart does not beat, there is no breathing, and their metabolism is practically absent. Is life over?
No, it stopped for a while. It is worth warming such a frog, it will move, come to life. The Siberian salamander newt freezes every winter and can spend up to ninety years (and maybe more) in this state.
Siberian salamander newt.
We ourselves and the many creatures around us are multicellular organisms. It is believed that such organisms have individuality, the ability to remember and gain experience. What happens if all the connections between cells are broken? What will happen to an individual?
A simple multicellular creature, the hydra, was trained to defend itself - to retract its tentacles in response to a flash of light. The hydra was then gently rubbed through gauze, breaking its body into individual cells. Hydra and sponge cells are able to reunite together after such an operation. It turned out that the reunited hydra remembered what it had learned, and also pulled in the tentacles.
Hydra (left) and a planarian worm.
In planarian worms, cells are unable to fuse after separation, but one planarian can absorb cells from another. It turns out that in this way the experience is also transmitted. That is, having taught a planarian something, and then feeding it a piece to another, you can transfer what you learned in this way. (This does not mean that you too, having eaten a mathematics teacher, will learn the Pythagorean theorem: our digestion and memory are arranged differently.)
Is it possible to create life yourself from the constituent parts? It turns out you can. Last summer, a group of scientists created DNA from scratch, hid it in a shell, filled this shell with ribosomes and everything necessary - and a new bacterium that had never existed before began to live, feed, and divide.
Another group of scientists have already learned to replace the "letters of the alphabet" of DNA - nitrogenous bases - with completely new ones.
Scientists dream that the new organisms they have created will be able to live on other planets in completely different conditions. Who knows, maybe we will become the very civilization that sows life on other planets …
