Early humans lived a Hunter-gatherer lifestyle. They must have evolved from apes that lived an Arboreal gatherer lifestyle. But between these two stages in human development, other stages must have gone unrecorded. During those stages, the apes became bipedal waders and runners, and their babies became buoyant swimmers. They lost body fur, lost threatening canine teeth, lost ape strength, and lost estrus signals that all land mammals have. They evolved blubber, a hooded nose, a large brain, a descended larynx, multi-pyramidal kidneys, loud-crying plump babies, and eccrine sweat cooling. Now they were human. They self-domesticated and developed grammatical syntactic language. So why did this all happen, and where did it all happen?

I think the unknown stages can be divided into two: the Aquatic-ape stage and the Free-sharing floater stage. Both stages may have occurred in a Galapagos-like scenario on the volcanic island Bioko, which had huge sea turtles to eat, and no predators to get eaten by. 

I think that about 6 million years ago a few chimpanzee-like apes became trapped on Proto-Bioko. With no forest foods or shelter on that barren island, they lived as Aquatic apes and evolved human features (see AquaticApe.net). Then perhaps 10,000 fully evolved naked humans populated the 200km-long coast of Bioko for 5 million years. These humans freely shared their aquatic habitats, and had no personal properties or territories. They shared their food, because a 300kg turtle provided too much meat for one family. They shared sex because no alpha males could dominate in the water. They shared babies who floated while holding on to the long head hair of mothers, fathers, children, and neighbors. They shared thoughts and feelings using song and language.

I think these obese buoyant humans lived mostly in the water as Free-sharing floaters. They ate shellfish, seaweed, and turtle meat in the water. They sang and talked in the water. They slept in the water, pooped in the water, had sex in the water, gave birth in the water, nursed babies in the water, died in the water, and buried their dead (about 200 deaths each year) respectfully in the water.

These billion or so humans (200 births each year for 5 million years) left no fossils or traces of their existence, because on rainy, warm, and safe Bioko they had no need for tools, weapons, shoes, clothes, or fire. Some Bioko humans, such as Homo erectus, Neanderthals, and Denisovans, went over to mainland Africa relatively early. They invented clothing, tools, and fire, and left fossils in some of the places they lived. But they were not as culturally advanced as the ones who stayed a bit longer on Bioko. When Homo sapiens from Bioko eventually met the less cooperative archaic humans in Africa and Eurasia, they more or less replaced them.