Final answer:
The complete replacement model, also known as the 'out of Africa' model, states that all modern humans originated in Africa and then spread out, replacing other human species. This is the prevailing model supported by genetic data and archaeological evidence such as fossils.
Step-by-step explanation:
The complete replacement model, or the "out of Africa" model, is a theory that suggests that all modern humans (Homo sapiens) originated in Africa about 200,000 years ago. According to this model, these early modern humans started migrating out of Africa around 100,000 years ago, gradually spreading across the other continents and replacing other hominin species, such as Neanderthals and Homo erectus. This model predominates in the scientific community, mostly because it is supported by a wide range of genetic data. In contrast, the multiregional evolution model suggests that Homo sapiens evolved from Homo erectus in several geographic regions concurrently, with a focus on explaining the diversity of modern human traits rather than relying heavily on genetic evidence.
Research from various fields such as archaeology, genetics, and anthropology, supported by fossils like the Neanderthal woman and Homo habilis, as well as by genetic studies, give credence to the replacement model. This model addresses the decline in human species diversity where only Homo sapiens survived roughly between 40,000 and 15,000 years ago. It also underlines the complex process of human evolution, and how modern scientific methods allow us to piece together historical evidence towards a coherent narrative of our past.