What made Darwin think humans evolved from monkeys?
Charles Darwin did not think that humans evolved from monkeys.
Rather, he believed, based on many years of research in the fields
of biology and comparative anatomy, that anatomically similar
species such as humans, apes, and monkeys probably evolved, over a
period of many thousands of years, from a common, ape-like
ancestor, now extinct. Recent studies in biology and genetics,
using techniques not available in Darwin's time, have confirmed and
further clarified his theory. In order to gain a further
understanding of Darwin's thinking, you might want to look up
"Charles Darwin" and "Evolution" in a variety of encyclopedias,
such as Wikipedia (en.wikipedia.org/wiki/Charles_Darwin). High
School and College textbooks of biology may also cover this topic
with more or less completeness. Many fine books have also been
written on this subject, including Darwin's "The Origin of Species
and the Descent of Man" and the fine biographical novel, "The
Origin," by Irving Stone.