What is life?

Life is, ironically, one of the greatest mysteries of science, philosophy and, ultimately, of any branch of human knowledge. It shapes us and surrounds us. It makes us be here and makes us exist. It is absolutely everything. But we don’t know what it is.

It is amazing to see how there is still no consensus when it comes to defining what life is. A set of organic matter that is nourished, related and reproduced? A being that dies? A genetic information that persists over time? An entity subject to evolution? And what about viruses? And with artificial intelligence? Why are we alive and a rock not? Where is the border between the “living” and the “inert”?

Do not expect to find answers today and here, because when it comes to defining what life is, science is mixed with philosophy and, after all, it must be everyone who finds the definition that helps them to be alivetag. But let’s dive into the nature of life. Clever?

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Entropy, DNA and the three vital functions: how do we define life?

The dictionary definition of life is, pay attention, the following: “existence of beings that have this property”. Thanks, you literally haven’t told us anything. But hey, let’s not judge. Actually, we are facing what is surely the most complicated definition in the history of mankind.Life is a great mystery .

At a biological level, we can define life as the set of physicochemical properties that distinguish the beings of the seven kingdoms (animals, plants, fungi, chromists, protozoa, bacteria and archaea) from inert and inorganic matter. It is what differentiates living beings from all other natural realities. But, ok, we are still left with doubts. Slowly.

We know that life arose on Earth about 3.8 billion years ago, just 700 million years after the planet’s formationand under extreme environmental conditions. In this context and despite the fact that its origin remains unclear (and surely never will be) life arose by simple chance.

In the primitive oceans, the molecules present in them were mixed to give rise to structurally more complex substances of an organic nature that ended up generating the first forms of life. Those from which we all come. Our universal common ancestor. But beyond this uncertain origin, what is life? What marked the border between the “living” and the “inert”? Well, it’s still uncertain. And to shed some light, it is time to talk about the three great concepts: entropy, DNA and the three vital functions.

Entropy: the order of life in the midst of the disorder of the Universe

Erwin Schrödinger, the famous Austrian physicist who made enormous contributions to quantum mechanics, once said that “Living Matter Escapes Natural Degradation towards Disorder and Equilibrium”tag. And this quote gave rise to one of the most interesting definitions of life.

From a physical perspective, then, we can define life as matter capable of going against the entropy of the Universe. But what is entropy? Well, today is disappointment day. Because the definition of entropy is also very complicated. It is often said that entropy is a force that causes everything in the Universe to tend towards disorder. But this is not entirely true.

Entropy is actually a consequence of probability applied to thermodynamicstag. Whatever is most likely to happen will happen. And in the Universe, as there are many particles forming the same system and randomness in it, by simple statistics, everything evolves towards the most probable state.

There is no force that pushes towards disorder. Everything moves away from order because, at a statistical level, what we understand as disorder is much (but very much) more likely than order. Is it possible that all of a sudden the molecules in a glass of water get just in the conformation so that, in full sun, a cube forms? If possible. But it is so infinitely unlikely that it simply becomes impossible in the time frame of the Universe.

But what does this have to do with life? Well, everything. And it is that the cells, those entities to which we put the label of “alive”, are capable of, as Schrödinger said,elude this tendency towards disorder and, thanks to their biological structure, maintain a constant order separated from the external disorder. .

We are alive because we don’t let the entropy that rules the Universe dominate us. At least, not so clearly. We avoid disorder and live in order. Therefore, we can understand life as that matter capable of maintaining molecular order in the midst of a Universe that pushes us towards disorder.

DNA: Selfish Genes and Life

We cannot try to define life without talking about DNA and evolution. Two concepts that are the cornerstone of life as we know it. And it is that in this sense,we can also define life as a lot of matter with a genetic loadtag. Yes, it sounds bland. But that’s what there is. Life can be understood as DNA molecules subject to the rules of the game of evolution.

But what is DNA? DNA, which stands for deoxyribonucleic acid, is a molecule that consists, in very short, of a succession of genes. Portions of this nucleic acid that carry information for a specific process in the body.

And these genes are, in turn, made up of chains of nucleotides, the smallest units of DNA. In fact, DNA is simply a sequence of nucleotides, molecules made up of a sugar, a nitrogenous base and a phosphate group.These nucleotides can be adenine, guanine, cytosine or thymine depending on how the nitrogenous base is .

So is DNA just a double helix made up of molecules that are little more than a sugar? Yes. It is what it is. But it is that nature has found that this molecular structure makes possible both the expression of genes (and genes give rise to absolutely all the proteins and molecules that make us alive) and their transmission from generation to generation. And here comes the concept of evolution.

Natural selection is the mechanism that makes the evolution of species possibleand consists of the process through which the genetic characteristics favorable to the survival of a species will be rewarded while the unfavorable ones will be lost. This is what, through adaptation to the environment, has made us go from a unicellular common universal ancestor to the infinity of living beings that currently inhabit the Earth.

Thus, we can understand life not only as the existence of genetic information that manages to guarantee the cellular complexity of a structure endowed with this life, but also as the phenomenon by which said information in the form of DNA survives over time, playing the game of evolution and natural selection and passing from generation to generation.

In fact, the famous British evolutionary biologist and scientific popularizer, in his famous work “The selfish gene”, published in 1976, proposed a definition of life that, despite being somewhat sad and even terrifying, serves as the climax for this section:

“We are survival machines, blindly programmed automatons in order to perpetuate the existence of the selfish genes that we harbor in our cells .” Life may be just that. The biological consequence that DNA has the nature of lasting over time Or is it something else? Let each one find the answer.

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The three vital functions: nutrition, relationship and reproduction

A third and final reflection on the meaning of life. Let’s talk about the three vital functions. And it is that in this context, we can define life as that organic structure (composed of matter that has carbon atoms as the central piece of its molecules) capable of nourishing itself, interacting and reproducing.

It is surely the most famous definition of life, but we have left it for last because it is also, in reality, the most confusing, the most controversial and the one that makes the definition itself take on more diffuse limitstag. But either way, let’s go deeper.

Following the thread of this definition, it is time to talk about the cornerstone of life: the cell. A cell is a space that forms the fundamental unit of life. And it is that absolutely all living beings on Earth are made up of at least one cell. In the case of the human being, by 3 million million.

A cell is the smallest organic entity to develop the three vital functions, consisting of a membrane that surrounds an internal liquid material known as cytoplasm where the different organelles make possible the millions of enzymatic reactions that allow this cell (and, in the case of multicellular beings, the organism) remains alive and continues to carry out these vital functions. In addition, it has a nucleus where the genetic information that we have talked about so much in the previous section is stored.

The cells have an average size of 10 micrometers (one thousandth of a millimeter), but that does not prevent them from being the units that give us life. And it is curious to see how the cell is alive despite the fact that absolutely all its structures are not considered alive. The membrane is not alive. Mitochondria are not alive. Enzymes are not alive. The endoplasmic reticulum is not alive. Nothing in the cell is alive but the cell is alive. That is why this definition is so diffuse.

Be that as it may, cells are alive because they have a membrane that allows them to separate from the outside (and thus maintain order within disorder), they make copies of themselves and are subject to the laws of evolution (which is why we have spoken of the DNA) and fulfill the three vital functions :

• Nutrition : The physiological process (or set of processes) that allows cells to transform matter into energy (in the case of heterotrophs) or energy into matter (in the case of autotrophs) in order to have both the fuel needed to maintain stable enzymatic reactions to dispose of the cellular elements and the pieces of matter necessary to conform to itself.
• Relationship: The physiological process (or set of processes) that allows cells to relate to both the external and internal environment. Capture information about what happens inside and outside in order to respond to it. Living beings are alive because they communicate with members of their species, flee from danger, respond to stimuli, change their state to adapt to the environment and, ultimately, because they interact.
• Reproduction: The mechanism that allows the transfer of genetic information over generations. Without this feature, the other two would be meaningless. It is the physiological process that, being sexual (by the union of gametes from two individuals of the same species and of different sex) or asexual (a cell divides to generate a clone of itself), allows the transfer of DNA to a new individual who will perpetuate the existence of the selfish genes that Dawkins spoke of.

It may seem like a clear and simple definition to say that life is an entity capable of nurturing, interacting and reproducing, but as we have said, its limits are more diffuse than it seems. And it is that although it allows to differentiate a human from a rock,what about viruses? Why don’t we consider them as living beings?Aren’t they related by parasitizing us, do they “reproduce” in their own way, generating viral replicas and “feed” on cellular structures?

And artificial intelligence? Wouldn’t a robot endowed with enough intelligence to relate to the environment in a human way, to feed on the energy that feeds it and to reproduce itself by generating computer copies of itself be a living being? Questions, questions and more questions that make the definition through the three vital functions more complicated than it may seem at first glance.

So what exactly is life?

As we can see, science has only been able to give us brushstrokes of the definition of life. We understand. But we don’t understand exactly what it is.We are unable to draw clear boundaries between what is alive and what is inerttag. But why does this happen?

Well, we must bear in mind that, in the end, we humans are the ones who, being simple groups of atoms that have developed thinking capacity, put labels. We do it with everything. We like to define, catalog and put borders between things. But the Universe does not understand categories.

Nature does not work by labels. It just workstag. And the line between the living and the non-living seems so thin because, in reality, there has never been a line. Life is a coincidence. We can call it a miracle or whatever we want, but after all it was a consequence of chemical phenomena that, after billions of years, has gotten out of hand.

Without human beings, there would be no “life”. But not because other organisms did not exist, but because no one had stopped to think about the meaning and definition of it. Life and death are irrelevant. We are entering philosophical terrain, yes, but after all, since we will never be able to find a universal definition, perhaps it is best for each one to have their own definition. Its own meaning. Life, in the end, is what you want it to be.