• Life was like "something else" before we became human beings, according to our partner The Conversation.

  • The first signs of life go back a very long time: more than 3.5 billion years ago!

  • The analysis of this phenomenon was carried out by Marion Tible, doctor in physiopathology and cell biology at Inserm.

This is a very complicated question and to make it (very) short, not all researchers agree on the answer!

To fully understand what is behind your question, you must first talk about evolution.

You understood it well, before being human beings, we were something else, we did not appear by magic on Earth.

We are part of a family called the Hominidae which includes, in addition to us, orangutans, gorillas and chimpanzees (our closest cousin).

This family is itself part of a larger family, the simiiformes (in which we find marmosets or baboons), which itself belongs to another large family, etc.

This classification is called a

phylogenetic tree

 : "tree" because it looks like a trunk that has a root that everyone shares, "phylogenetic" because it comes from the ancient Greek phylon, which means family, and genetics, which explains what we are by looking at our genes, these little things found in all the cells of your body and which define the color of your eyes, the size of your heart, your height ...

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What differentiates us from the other branches of our tree are mutations (small changes in our cells that cause them to become a little different from the ones before).

They take place in our genes and have allowed humans to adapt to their environment and become what they are today: for example, walking on two legs, having a bigger brain, to be able to speak… This is called natural selection, and Charles Darwin is the first scientist to have demonstrated this.

But then, if we are the result of all these adaptations, where do we come from in the beginning?

The first signs of life go back a very long time, over 3.5 billion years ago.

At the very beginning, there were only small cells, called bacteria, which evolved to reproduce faster, better, and in all environments (hot, cold, in water, on earth).

The cells became groups of cells, then increasingly complicated beings, with organs, particular functions, specificities for each role (fins in the water, legs on the ground, wings to fly), up to us!

We are ultimately the result of billions of years of evolution, and we are still evolving.

Diagram showing the geological timescale © United States Geological Survey / Wikimedia CC BY-SA 4.0

So we know that we are descended from bacteria, but how did life appear on Earth?

You must first understand that, in order to exist, a living being must build itself and for that, it uses small bricks, like Lego that you stack to build a castle, called DNA and RNA.

It is on these bricks that the genes mentioned above are located: they contain all the information needed to make a living being and allow it to reproduce.

For this DNA and RNA to exist, it takes smaller blocks called nucleic acids, which are themselves made of atoms, such as carbon, oxygen or nitrogen.

These atoms, you know them, they are everywhere, in the air that you breathe (oxygen and nitrogen), in the wood of the forests (carbon, oxygen and other things) and therefore, in your body.

It's tiny, you can't see them, but they are there and they are all there is.

Composition of DNA and RNA © Sponk / Vikidia CC BY-SA 4.0

At the birth of the Earth, there were already atoms.

They joined together to form the first nucleic acids, then the first RNAs, the first DNAs and finally the first bacteria.

How these early associations came about is where scientists don't quite agree and don't have all the answers.

Our “Evolution” file

After all, that was a really long time ago and we don't have all the information to answer this question.

Today, researchers think it's a mix of chance (yes, it's a bit lucky to have all these atoms at our disposal and put them together properly!), Different failures and affinity between the atoms on Earth that gave birth to life.

Others believe that the asteroids which have struck the Earth over time may have brought other atoms and favored the appearance of life.

Still, life arose through the association of atoms, and although we are not sure how, we are glad that it happened and that the Earth was able to form very complex human beings. , like you !

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This analysis was written by Marion Tible, doctor in physiopathology and cell biology at Inserm.


The original article was published on The Conversation website.

Declaration of interests

Marion Tible does not work, advise, own shares, receive funds from any organization that could benefit from this article, and has not declared any affiliation other than her research organization.

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