D. A possible answer to a scientific question
This is known as parasitism.
In biology, parasitism is a relationship between species, where one organism, the parasite, lives on or in another organism, the host, causing it some harm, and is adapted structurally to this way of life.
The best answer would most likely be genetics or genetic theory.
There were many doubts about Darwin's theory because Darwin could not yet describe the mechanism of inheritance. Mendel's work on inheritance was already published, 2 years earlier, but this eluded Darwin. It was only till after Darwin's death that the science of genetics came about.
This union brought about the "modern synthesis," a theory that proposes that both genetics and natural selection is a result of evolutionary changes.
