Final answer:
The earliest migration of human ancestors out of Africa occurred in a single wave, according to the theory that Homo ergaster migrated out of Africa around 1.75 million years ago and settled in various regions.
Step-by-step explanation:
The earliest migration of human ancestors out of Africa is best described by statement a) It occurred in a single wave.
This is supported by the theory that Homo ergaster, an early species of the genus Homo, began migrating out of Africa around 1.75 million years ago, moving northward into Eurasia. They settled in various regions, such as eastern Europe and Java, and likely traveled by land routes during the Pleistocene Ice Age when sea levels were lower.
Based on current evidence, it is believed that this migration occurred in a single wave, rather than multiple waves at different times.