Darwin’s Theoryby Federico Brovelli

Charles Robert Darwin

Charles Robert Darwin (12 February 1809 – 19 April 1882) was an English naturalist. He established that all species of life have descended over time from common ancestors, and proposed the scientific theory that explains that this branching pattern of evolution, resulted from a process that he called natural selection.

Darwin published his theory with some evidence for evolution in his book “On the Origin of Species”, overcoming scientific rejection of

earlier concepts of transmutation of species. By the 1870s the scientific

community and much of the general public had accepted evolution as a

fact.

However, many favoured competing explanations and it was not until the emergence of the modern evolutionary synthesis from the 1930s to the 1950s that a broad consensus developed in which natural selection was the basic mechanism of evolution.

In modified form, Darwin's scientific discovery is the unifying theory of the life sciences, explaining the diversity of life.

The journey on the Beagle

The Beagle was a ship used for a cartographic consignment of five years, around the coasts of South America. When Darwin was young, he was recommended to

Robert Fitzrov, the captain of this ship.

The possibility of working, during the journey directly on

the field, allowed him to study the geological characteristics of continents, islands, and a lot of

organisms and fossils. He collected methodically a large amount of samples, unknown to science: this samples, were given to British Museum, and

only those samples were an enormous scientific

contribution.

Thanks to those studies Darwin began detailed investigations and in 1838 conceived his theory of natural selection. Although he discussed his ideas with several naturalists, he needed time for extensive research and his geological work had priority.

He was writing up his theory in

1858 when Alfred

Russel Wallace sent him an essay

which described the same idea,

prompting immediate joint

publication of both of their

theories.

Darwin’s WorkDarwin's work established evolutionary descent with modification as the dominant scientific explanation of diversification in nature.

In 1871 he examined human evolution and sexual selection in The Descent of Man, and Selection in Relation to Sex, followed by The Expression of the Emotions in Man and Animals.

How Darwin conceived his idea

He based his theory on fourth different evidences Direct Observation

Biogeography Fossils

Homologous Structures

Direct Observation

The first evidence is the direct observation. The first object of his interest were the artificial selection. He talked a lot about

the intersection of pigeons: in order to obtain a thinner beak or larger wings. In general, the artificial selection, is the selection

operated by man. Voluntary (like the intersection between species) or not.

To explain the second case, we could talk about the Biston Betularia.

Biston betularia is a white moth, which lives

in Manchester. In the '800 a lot of factories

were born in this territory.

Slowly the white moth was

replaced by the black moth.

Why? Because the trees, contaminated by smokes, had become black, and the white moth, resting on these trees,

became targets for the raiders, and because of the contrast it

couldn't camouflage. Slowly the darkest moth replaced the

clearest one, until the clear ones disappeared. When an animal

changes its colour to camouflage because of any change in the

environment or because of the humans, we talk about industrial

melanism.

BiogeographyThe second evidence is biogeography. Darwin had noticed that in the same area, there were different types of creatures and species. Biogeography was the weapon to destroy the idea of creationism. But the numerous examples of different species in the same area, were only a support to the evolution theory: every single animal is different, because they have different needs, and different ways of surviving.

Fossils

The third evidence were fossils. During his journey on the Beagle, Darwin

studied a lot of them. He discovered a substantial difference between ancestral

creatures and modern ones. Unfortunately, this wasn’t enough, because nothing proved a gradual

changing from a primitive form. For this reason Darwin described this evidence as

“little remarkable”.

Homologous StructuresThe fourth evidence was the discover of a homologous structure that was shared by every single creature on Earth. The same starting DNA sequence shows us the common origin of the species.

As we can see in the image, different creatures share the same basic structure. This structure was particular of an animal called ancestral tetrapode, or more precisely Silvanerpeton Miripedes.

An Incompleted TheoryDarwin lacked of precision, and in his theory he didn’t explain the origin of the variation that permitted the evolution, but for that we have to wait until the XX century, when Mendel would analyse this matter.

THE END