One of the questions many have sought to answer, "Why Mendel was not acknowledged as having made a significant breakthrough in his own lifetime?". The answer which has been given is that he published in an obscure journal and nobody really read his paper until the 1900's.
This is not quite correct. Charles Darwin actually had a copy of his paper but appears not to have read it. The paper was discovered in book on plant hybridisation. Books published at the time frequently required the purchaser to cut the pages open. In this collection of papers Darwin opened and read some papers but ignored Mendel's and left the pages sealed.
Below is a time scale showing the approximate dates of publication.
Linnaeus started defining plant species before moving on to animals. He is credited with starting taxonomy and defining the term species.
Lamarck presented his theory of the inheritance of acquired characteristics as a model of how animal species developed. In France he is still treated as the father of evolution. He didn't get it all correct but neither did Darwin (genetics).
Malthus published an essay pointing out the mathematical problem of reproduction outstripping the available food supply. It was very influential on Darwin and Wallace.
Lyell was important in challenging the prevailing idea of catastrophie in geology. This laid the foundation of uniformitarianism (geological processes in the past operated at the same rate as today) which ascribed millions of years to the age of the earth. This was in sharp contrast to the assumed young age for the earth and the interpretation of geological formations as caused by floods and volcanic erruptions.
Darwin published his book on the origin of the species yet without any real knowledge of inheritance.
Mendel's work opened the door to the proper understanding of genetics. However it did also suggest that there were limits to variation.