The correct answer to the question is:
D. climate change
1. **Explanation:** Historians believe that climate change was a significant factor that most likely caused human migration out of Africa into other areas of the world. During periods of climate change in Africa, such as the Ice Ages, the environment became more challenging for early humans to survive. As a result, they had to adapt and move to regions with more favorable climates and resources for sustenance.
2. **Additional Information:** Human migration out of Africa is a complex process influenced by various factors, including environmental changes, population pressures, and the search for new opportunities. While climate change played a crucial role, it is essential to consider that multiple factors could have contributed to the movement of early humans across continents over time.
