What evidence, when Darwin/Wallace began work made them think of evolution?

nj writes:And then somehow from this logic he came to the grand notion that all plants and animals share a common ancestor.

Chiroptera writes: ...it is only the beautiful writing style of 19th century authors that keep the books at all readable.

RickJB writes:Why not read Darwin's The Origin of Species and find out how?

Magecraft writes: "What was the evidence that was accumulating when Darwin and Wallace began their work that led them to start thinking about evolution?"

1. Transmutationism (also called by Darwin "Descent with Modification"). This word means in context that species change ("mutate", from the Latin) from one species to another. It is in opposition to the prevailing Aristotelian views that species were natural kinds that were eternal.2. Common descent. This is the view (not held by all evolutionists prior to Darwin or even after) that similar species with similar structures (homologies) were similar because they were descended from a common ancestor. Darwin tended to present the cases for limited common descent - i.e., of mammals or birds - but extended the argument to the view that all life arises from a common ancestor or small set of common ancestors.3. Struggle for existence. This is the view that more organisms are born than can survive. Consequently, most of those zygotes that are fertilised will die, and of those that reach partition (birth) many will either die or not be able to reproduce. The competition here is against the environment, which includes other species (predators and organisms that use the same food and other resources). This is interspecific (between species) competition.4. Natural selection. This is a complex view that species naturally have a spread of variations, and that variants that confer an advantage on the bearer organisms, and are hereditable, will reproduce more frequently than competitors, and change the "shape" of the species overall. Notice here that this competition is mostly intraspecific, i.e., between members of the same species (and indeed of the same population).5. Sexual selection. Many features of organisms are obvious hindrances (such as the tails of birds of paradise), and these often occur in one sex only. Darwin argued that there was competition for mating opportunities and any feature that initially marked a gender out as a good mating opportunity would become exaggerated by the mating choices of the opposite gender. Competition here is between conspecifics of the same gender.6. Biogeographic distribution. Darwin and Wallace were concerned to explain why species were found in the areas they were, and argued that dispersal of similar, but related, species was due to their evolution in one place and migration into other regions.7. Heredity. Darwin knew very little about what we would call the principles of genetics. He accepted the prevailing and old view that the use of features of the organism would change the way those features were inherited.

Vashgun writes: yeah, what was the evidence that was accumulating? I read that it was obvious but I don't understand what was obvious.