Final answer:
The climatic region with traditionally small human populations, high biodiversity, many parasites, and warm temperatures year-round is the rainforest.
Step-by-step explanation:
The climatic region described by traditionally small human populations, a variety of plant and animal life, many human parasites, and warm temperatures year-round is the rainforest. Rainforests are known for their extensive biodiversity, including both flora and fauna, and for sustaining numerous parasites due to the warm and moist environment which is ideal for their propagation. In contrast to arid regions like deserts or the cold and sparsely vegetated tundra, rainforests have consistent rainfall and support a dense network of life, including small, often indigenous human populations that have adapted to the environment.