On what biological theory was Social
Darwinism loosely based? Who developed Social
Darwinism, and what was the theory's basic idea?
What beliefs and conditions was Social Darwinism used
to justify?

Social Darwinism is a belief, popular in the late Victorian era in England, America, and elsewhere, which states that the strongest or fittest should survive and flourish in society, while the weak and unfit should be allowed to die. The theory was chiefly expounded by Herbert Spencer, whose ethical philosophies always held an elitist view and received a boost from the application of Darwinian ideas such as adaptation and natural selection.

Explanation: I take History also and somehow remembered this exact question.