Out of Bioko theory of human evolution
Out of Bioko theory (OOB) is not the same as Out of Africa theory (OOA). In the following summary, ages and other details are debatable (obviously).
8 Myr. Chimpanzees and gorillas split from a common knuckle-walking ape ancestor in western-central Africa. The split occurred because gorillas chose low quality foods that were always available. They evolved a larger body. Chimpanzees chose higher quality foods that required more searching and more tree climbing.
6 Myr. A few chimpanzees became trapped on a tree floating in an African river, and rafted out to the Atlantic Ocean. They stranded on Proto-Bioko, an evolving group of barren volcanic islands. They couldn't escape. The chimps survived by eating crabs and seaweed, and eventually learned to swim. They lived mostly in the sea, which provided all of their food. They walked upright in neck-deep water. The jagged volcanic rocks of the island were uncomfortable to walk or sleep on, so the chimpanzees' descendants slept on beaches or nests of floating seaweed. There were no large predators on Bioko (also none today). There were no African parasites or viruses on Bioko, which explains why human DNA is somewhat non-African. It was always warm and nearly always cloudy or rainy on Bioko (as today), so hair was not needed for warmth or sun protection. The Bioko semiaquatic apes evolved bald bodies, subcutaneous fat (blubber) for buoyancy and insulation, descended-larynx and voluntary breath control for mouth-breathing and diving, and all other unique human features. The apes eventually discovered that they could live comfortably on sea-turtle eggs and sea-turtle meat (also available today in immense quantities on Bioko beaches), supplemented by seaweed and shellfish. Because of abundant food with little effort, there were thousands of these fat floating apes along the 200 km-long coastline of Bioko (not unlike the 200,000 marine-iguanas that currently live along the shores of Galapagos islands). The large population remained stable for millions of years, while humans evolved their unique anatomical features, language, concealed-estrus, frontal sex with unreliable female orgasms, and self-domesticated culture.
4 Myr. Some bipedal small-brained Bioko apes swam to mainland Africa, where some hybridized with gorillas and chimpanzees. Their various descendants wandered to drier parts of Africa, where they left Australopithecus-fossils.
2 Myr. Some chimpanzees (Pan troglodytes) of central Africa became isolated on the south side of the Congo River and evolved into the bonobo (Pan paniscus), due to genetic drift. Because of similar habitats, there were no strong selection pressures to promote rapid evolution.
2 Myr. Chimpanzees were isolated by major rivers in central and western Africa, and evolved into the four modern subspecies of chimpanzee (no strong selection pressures). Similarly, isolated gorillas evolved into the four modern subspecies of gorilla (no strong selection pressures).
1.5 Myr. By this time, humans on Bioko had evolved large brains (which consist mostly of DHA-rich fat), as a result of the DHA-rich marine diet and the selection pressure for general fat-accumulation. Some large-brained humans walked to mainland Africa during geological periods of low sea level (during glaciations of the northern continents). To compensate for their pathetically weak, unprotected, and slow-running bodies, they used their large brains to invent clothing, shoes, tools, and weapons, which were needed to deal with harsh sun and dangerous predators. They migrated to places where Homo erectus fossils have been found (East Africa, Europe, Java, China.)
0.8 Myr. Some humans left Bioko, invented clothes and weapons, and migrated to places where Neanderthal and Denisovan fossils have been found.
0.3 Myr. Some humans left Bioko, invented clothes and weapons, and migrated to places where Homo sapiens fossils have been found.
0.05 Myr. The last humans left Bioko only about 50,000 years ago. They invented clothes and weapons, and spread out to all the continents. Those who went north evolved lighter skin that could absorb vitamin D. Others evolved darker skin that shielded against ultraviolet rays. (Chimps have intermediate-colored skin, as seen best in hairless chimps that have alopecia). Neanderthals, Denisovans, and all races of Homo sapiens are the same species, with some genetic and phenotypic differences. Semiaquatic humans were wiped out by terrestrial humans who returned to Bioko while it was connected to the mainland during the most recent period of low sea level (c. 70,000-10,000 years ago.) The returning humans had developed their foreign language, culture, and religion in mainland Africa, and using their weapons, they carried out the world's first genocide on Bioko.
According to this hypothesis, all humans and prehumans are "Out of Bioko" but it is misleading to say "Out of Africa".