They thought all the creatures of the planet had been conceived by divine force.

That is, until Charles Darwin arrived.

Some researchers were already talking about an evolution of the species, But the British naturalist is the first to explain with evidence how evolution might occur by natural selection.

His theory radically changed biology, offering a new explanation of the origin off human beings.

It also made him one of the most influential scientists and intellectuals in history.

But to get there, he had to make an extraordinary journey, perform hundreds of experiments and spend 20 years refining his ideas.

In 18 31 Darwin was 22 years old and studying at the University of Cambridge when he was invited as a naturalist to a great expedition.

He boarded the hatred Spiegel and spent almost five years traveling several continents, starting in South America, from which he brought back dozens of life specimens illustrations on fossils.

These fossils gave him one of the first clues about evolution, for example, observing the remains of a mile Uddin, a giant animal similar to the sloth.

He thought that those similarities were probably not a coincidence.

There had to be some kind of link when he stopped to the Galapagos Islands.

Darwin also observed its giant tortoises, which lived in nearby islands but showed unique physical characteristics in each island.

In the humid areas where vegetation was abundant, the turtles had a short neck on a dome shaped shell.

Whilst in the islands with a drier environment, they had a satellite shells under longer neck.

But could he explain that difference?

Upon his return, Darwin spent time observing how and more breeders in guarded crossbred animals of species to create new varieties.

For that creation to be successful, the artificial selection made by Man was key.

Darwin realized that the natural world probably made the same kind of selection, but he could explain how it happened until he read the work of Thomas Robert Malthus, a British intellectual from the 18th century.

In an essay on demography, Martha said that as the population in Europe was growing at one point, it would increase much more than the food supplies available, and that would cause a fight for survival.

This idea helped Darwin explain how evolution works in nature.

There is a struggle for survival in which the strongest individual is not necessarily the survivor.

Instead, it's the one which best adapt to the environment where it lives.

If a living being has any trait that helps him to survive, it will be more successful.

Reproduction.

Those which don't adapt will die without descendants, creatures with the most success in reproducing past their traits to their lineage and so on until these variations end up becoming a new species.

That's why the differences between the Galapagos tortoises were a product of evolution in a dry environment.

Those with longer next could reach the bushes easily in order to get food while stays who lived in the human environment could eat grass and protect themselves from predators thanks to their shorter neck on the dome shaped shell, Darwin said that all species, including humans, were not created independently, but they descended from a common ancestor from their non life on the planet began to diversify 20 years after his trip, Darwin had written thousands of pages, but he had unpublished any.

He wanted to have irrefutable evidence, perhaps because he knew that his theory was going to cause quite a stir.

But everything changed when he received a letter from Alfred Russel Wallace and admirer and a fellow naturalist who told him that he had reached the same conclusion.

Evolution was produced by natural selection.

Darwin panicked, facing the possibility that Wallace could take sole credit for the theory.

So the two naturalist agreed to present a joint letter explaining their findings.

But a year later, Darwin published his book, titled On the Origin of Species, and he became a celebrity way beyond the scientific communities.

His findings shook the foundations Victorian, Britain, Copernicus.

In his time, Darwin changed the game by explaining that diverse came from a biological process without any interference from God.

Darwin put human beings in the same evolutionary level as all the creatures on the planet.

Scientific advances have confirmed his theory, and even the Catholic Church ended up accepting decades later that evolution is compatible with faith.

And today, more than 100 50 years after Darwin's theory became known, we know that evolution is a fact.