Final answer:
The primate group with the fewest current world species is the prosimians, including lemurs, bush babies, lorises, and tarsiers, which are generally smaller and nocturnal.
Step-by-step explanation:
The primate group that has the smallest number of current world species is the prosimians. This ancient group includes the lemurs of Madagascar, the bush babies of Africa, and the tarsiers and lorises of Southeast Asia. As compared to other primate groups like anthropoids, which include monkeys, apes, and humans, prosimians tend to be smaller, nocturnal, and have relatively smaller brains. Over the course of evolution, many early prosimian species went extinct, leading to the lower diversity of species we see today in this group.