In a study concentrated on primate aggression, researchers wanted to observe primates in conflict. The Japanese macaque is the northernmost-living nonhuman primate. He began his career with nonhuman primate research. Studies strongly suggest convergent evolution in spotted hyena and primate intelligence. Some zoologists and scientists wondered what made humans different from animals in the primate family. Such neurons have been directly observed in primate species. A study of the response of non-human primate to the vaccine had been initiated. Theories were proposed based on observations of non-human primate paintings. Coat color is sometimes sexually dimorphic, as in many primate species. About 60% of primate species are threatened with extinction. FIV displays a similar structure to the primate and ungulate lentiviruses. There are nine recognised species of this small-bodied nocturnal primate. More than 90% of primate species occur in tropical forests. It is thought all nine recognised species of this small-bodied nocturnal primate are venomous. Additionally, 75% of primate species have decreasing populations.