Final answer:
The species first to migrate out of Africa around 1.75 million years ago was Homo ergaster, according to the multiple origin theory. Homo erectus also played a crucial role in early human migration and spread to Eurasia.
Step-by-step explanation:
According to the multiple origin theory, the species that was first to migrate out of Africa about 1.75 million years ago was Homo ergaster. This early human species is believed to have moved northward into Eurasia, marking one of the first waves of human migration. Other theories suggest that an earlier hominin, such as an australopithecine or unknown species of the genus Homo, could have left Africa around 2 million years ago, potentially leading to the settlement of Dmanisi hominins in eastern Europe. Homo erectus is another significant species in the story of early human migration, which evolved approximately 1.9 million years ago in East Africa and later spread to Eurasia.