Science has also been analyzed by sociologists, political scientists and literary critics, who make little or no effort to understand the scientific … - Mordechai Ben-Ari

Social Darwinism and eugenics are unscientific in two aspects. First, they commit the naturalistic fallacy, which is the assumption that what is, must be. The fact that the natural environment selects for reproductive advantage does not mean that we, as humans, should be forcibly selecting people according to some preconceived notions. The second nonscientific aspect of these movements was their narrow interpretation of the meaning of fitness. In evolution, this simply means fitness to survive and reproduce, not fitness according to some externally imposed criteria.
Darwin himself never engaged in these speculations, nor did he support these perversions of his theory.

We can define a fact as an observation backed up by such a preponderance of evidence that no useful purpose would be served by doubting it.

A scientific theory is a concise and coherent set of concepts, claims, and laws (frequently expressed mathematically) that can be used to precisely and accurately explain and predict natural phenomena.
A theory should include a mechanism that explains how its concepts, claims, and laws arise from lower-level theories.