Final answer:
Early Homo species may have left Africa as far back as 1.75 million years ago, with Homo ergaster moving into Eurasia and possibly an earlier unknown hominin reaching Europe by 1.85 million years ago. The settlement of Homo erectus on Java between 1.3 and 1.6 million years ago also supports early migration out of Africa, with sea levels facilitating travel routes.
Step-by-step explanation:
The controversial evidence for early Homo species leaving Africa by 1.7 million years ago or earlier encompasses various archaeological findings and theories. One theory suggests that Homo ergaster began migrating out of Africa around 1.75 million years ago, heading into Eurasia. Another posits that an earlier hominin species migrated out of Africa about 2 million years ago, which may have given rise to the Dmanisi hominins in eastern Europe by 1.85 million years ago. This early migration is evidenced by the settlement of Homo erectus on Java between 1.3 and 1.6 million years ago, facilitated by lower sea levels during the Pleistocene Ice Age. These theories are surrounded by academic debate due to the imprecision of dating methods and the potential for new discoveries that could reshape our understanding of human migration.