It may look like that from a distance, but this is really not true. Darwin’s success was built on the foundation of a century or two’s careful work building up of an understanding of taxonomy and solid skills that allowed reliable and reproducible identification of species. There are good reasons why earlier versions of evolutionary theory convinced very few people (and why Darwin himself found them such an embarrassment that he was reluctant to put his own theory forward). Darwin (and Wallace) were really the first people able to build up a solid case, and it was built on the basis of the labors of hundreds of natural historians, both refining their taxonomical craft and building up a large catalog of well verified biological facts and reliably differentiated species, through the 18th and early 19th centuries. Darwin himself wsa very much aware of this, and held off announcing his theory until he himself had developed the skills and reputation of an expert taxonomist (which he had not had at the time of the Beagle voyage). It took him almost 20 years.
And that is not to mention the work in geology that hugely expanded the age of the Earth, thus giving enough time for evolutionary processes to happen. It is really not until the late 18th century that advances in geology begin to give anyone anyone any reason at all to believe that the Earth is more than a few thousand years old, and it is not until the work of Lyell, in the 19th century, that a solid case for an age in the millions of years was built up. Lyell was an older contemporary (and, eventually, personal friend and mentor) of Darwin, and far and away the most important scientific influence on his thinking. Darwin, who had already done field work with Sedgewick, perhaps the best field geologist of the time, read Lyell’s work during his first few weeks on the Beagle, when it was newly published, and it changed his life.
The ancients had nothing like any of this. They just had loose speculation (as in Anaximander) and unsystematic collections of, often unreliable, natural-historical anecdotes (as in Aristotle’s and Pliny the Elder’s natural histories).