Scientist
Theory
Social and political influences
Jean Baptise Lamarck
Lamarkism
Creatures develop traits during their lifetime and pass these traits to their offspring
E.g. in reaching higher leaves giraffes stretch their necks and the acquired longer neck to off spring

He proposed the changes were natural not divine therefore his theory was not as disparaged by religious groups as other evolutionary theories.
Lamarckian-influenced political theorists in the socialist ranks often combined his scientific theory with a natural law philosophy, which advocated equal rights and liberty for all human beings. Naturally, this shook the upper class quite profoundly; they balked at the thought of working class riff raff engaging in scientific discourse, let alone riff raff questioning the "natural" order of things. Lamarckian postulation was disturbing to the educated gentleman because it was a threat to his world view.
Lamarck's theory of evolution was based on two presuppositions, which were based on his Zoological Philosophy published in 1809. The first was that there is in organisms a tendency toward perfection and increased complexity which begins with the simplest species (presumably single-celled animals) and progresses until it arrives at the most developed species (Homo sapiens). The second presupposition is that of adaptive traits: when an organism meets new demands in its environment, physiological changes begin to occur which help that organism meet that demand. The new traits are then passed on by heredity, and thus species evolve.
Lamarck’s theory was disproven by August Friedrich Weismann experiment “901 mice without tails” in 1891.
Charles Darwin
Natural selection Evolutionary change comes through the production of variation in each generation and differential survival of individuals with different combinations of these variable characters. Individuals with characteristics which increase their probability of survival will have more opportunities to reproduce and their offspring will also benefit from the heritable, advantageous character. So over time these variants will spread through the population.
E.g Giraffes that already have long necks survive better- leave more offspring who inherit their long necks- variation
Selection and survival
Reproduction and inheritance of more fit traits
By the beginning of the 19th century, a great deal of evidence was available to the scientific community that supported evolution. What was missing was a plausible mechanism to explain how evolution was occurring. Charles Darwin and Alfred Wallace independently arrived at evolution as a result of natural selection. Darwin gathered evidence after sailing on the HMS Beagle to South America and the Galapagos Islands. By the early 1840s, he had documented the main points of his theory.

Wallace was a British naturalist working in Indonesia in the mid-1850s. In 1858, Wallace sent a copy of his work to Darwin. Darwin's colleagues encouraged him to publish The Origin of Species at the same time and so receive the credit for his years of work and insight. The Origin of Species included overwhelming evidence to support Darwin's conclusions. Even though the Darwin/Wallace theory of natural selection caused a furore amongst Victorian society in England when published, scientific thinking was gaining respectability and becoming an important mechanism for change.

The theory of evolution has encountered opposition since it was first introduced. This is because it can be seen as a threat to religious and social beliefs

Christianity was a very dominant force during the time of Charles Darwin.
Creationism was widely accepted, as a religious and a scientific concept Darwin knew what a huge impact his knowledge would make on the world when he released it, so he withheld his theory for 25 years. It was only when he felt the social and political climate was right, did he publish his information He chose to publish it during a time of great