When Charles Darwin published
The Origin of Species in 1859, it was already known that existing species can change over time. This is the basis of artificial breeding, which had been practiced for thousands of years. Darwin and his contemporaries were also familiar enough with the fossil record to know that major changes in living things had occurred over geological time. Darwin's theory was that a process analogous to artificial breeding also occurs in nature; he called that process natural selection. Darwin's theory was also that changes in existing species due primarily to natural selection could, if given enough time, produce the major changes we see in the fossil record.
After Darwin, the first phenomenon (changes within an existing species or gene pool) was named "microevolution." There is abundant evidence that changes can occur within existing species, both domestic and wild, so microevolution is uncontroversial.
The second phenomenon (large-scale changes over geological time) was named "macroevolution," and Darwin's theory that the processes of the former can account for the latter was controversial right from the start. Many biologists during and after Darwin's lifetime have questioned whether the natural counterpart of domestic breeding could do what domestic breeding has never done -- namely, produce new species, organs, and body plans. In the first few decades of the twentieth century, skepticism over this aspect of evolution was so strong that Darwin's theory went into eclipse. (See Chapter 9of Peter Bowler's Evolution: The History of an Idea, University of California Press, revised edition, 1989).