How did Charles Darwin explain evolution

Charles Robert Darwin (born February 12, 1809, † April 19, 1882)

With his work "On the Origin of Species", the natural scientist Charles Darwin completely changed the worldview of humans and the history of creation, which had hardly been questioned until then. And that although Darwin himself was a studied theologian and initially struggled with the publication of his theory because he knew about the consequences. He formulated his theory from the observations of his voyage over Tenerife, Cape Verde, Cape Town, Sydney, New Zealand and the Galapagos Islands and coined the term "survival of the fittest", i.e. the survival of those who are best adapted to the environmental conditions in which the strongest pass their genes on to the next generation in the "Struggle for life" (competition for resources).

Darwin's theory consists of several assumptions:

Reproduction: Individuals in a population always produce more offspring than would actually be necessary to preserve them.
Variation: The individual individuals in a population are never the same. They differ in several characteristics.
Selection: Those individuals who happen to be better adapted to the prevailing environmental conditions than others have a selection advantage and survive more often. As a result, they can bring their genes (including their characteristics) into the next generation more often than individuals who are not so well adapted.
Inheritance: Variations in the traits are to a certain extent inheritable.

In summary, it can be said that long-term selection leads to a natural selection of individuals of a species that are, by chance, better adapted than their conspecifics. As a result, the characteristics of a species change over many generations.

Darwin's theory from today's perspective:
Darwin recognized the random occurrence of new features within the respective species, but could not explain where this change came from. It was only genetics in the 20th century that could explain this random change in characteristics through recombination and mutation and scientifically confirm Darwin's theory. Today Darwin's theory serves as the basis for the synthetic theory of evolution.