Simians, commonly known as primates, are a diverse group of mammals that include monkeys, apes, and humans. They are characterized by their flexible limbs, forward-facing eyes, and complex social behaviors. Simians are primarily found in tropical and subtropical regions, and they play important roles in their ecosystems, often acting as seed dispersers. There are two main subgroups of simians: New World monkeys and Old World monkeys. New World monkeys are found in the Americas and often have prehensile tails, while Old World monkeys are native to Africa and Asia and do not possess this feature. Both groups exhibit a wide range of sizes, diets, and social structures.