Humans are not descended from any modern species of monkey; both monkeys and humans are descended from some long-extinct ancestor pre-dating both. Although this species, if it were transferred to today, would be considered a "monkey", it is not any living species of monkey, further more evolution is the change in populations, not in individuals. Humans actually developed from a primate ancestor, but not an extant species of monkey or ape. and lastly evolution can lead to what we call Speciation, this occurs when something branches into two or more reproductively isolated populations or when a single species change over time to such an extent that the latter population is considered a different species. i hope this clears up some of your misunderstandings, let me know if you have questions