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Submitted edit of Aquatic Ape Hypothesis page on Wikipedia

Allan Krill
 
Edited

Bioko island postulated to be the aquatic location

Bizarre creatures sometimes evolve on islands, a phenomenon known as the island syndrome. Geology professor Allan Krill recently suggested[74] that humans evolved by peripatric speciation on a barren volcanic island, in a scenario similar to that of the Galapagos Marine iguana. The chimpanzee-human last common ancestor may have accidentally rafted to proto-Bioko island of western Africa. As with the iguana, these arboreal animals may have been stranded with no forest foods, and their exclusively marine diet and semiaquatic habitat resulted in unique anatomical changes. Bioko has a rainy climate with neither strong sun nor cold nights, so body fur would not be as necessary there. Bioko has no large predators, so primates evolving into vulnerable humans could survive there without inventing weapons. Beaches on Bioko are visited by many sea turtles each night during much of the year, so turtle eggs and meat could have been shared by semiaquatic humans without tools or fire. Plentiful marine food may have supported large coastal populations, as with the marine iguana. Dense habitation may have led to self-domestication and Proto-Human language. Some hominins may have left Bioko and invented clothing, tools, and fire, that were necessary elsewhere. Because the warm humid climate of western Africa causes bones to decay rapidly, no mammal fossils have ever been reported from Bioko or any areas inhabited by chimpanzees or gorillas. Therefore there is no fossil evidence for chimpanzee or gorilla evolution, or for an early human presence on Bioko. If there was an average population of 10,000 semiaquatic humans on Bioko for 5 million years, this would be one billion people. The corpses of the 200 people who would have died each year could have been buried respectfully in the sea. Genetics might be able to test the Bioko hypothesis. Complementing the recent African origin of modern humans it seems possible that Neanderthals and early modern humans came directly from Bioko while it was connected to the mainland by a Pleistocene land bridge.


Where, when, & why did humans originate?

Allan Krill
 

The earliest Y-chromosome DNA (A00) and language (Khoi-San with 'clicks') are in west Africa, from about 200,000 years ago.
But how could anatomically modern humans suddenly start there, having left no fossil record of their earlier history?  
I think humans evolved on Bioko Island in a Galapagos-like scenario.

Chimpanzees live in western Africa where there are no fossils of any mammal, because bones decay too fast. About 6 million years ago, a few chimps accidentally rafted 32 km to the volcanic islands of Proto-Bioko. There were no trees or predators. Their only food was seaweed, shellfish, turtle eggs and turtle meat: hundreds of huge sea-turtles visit the beaches each night to lay eggs.

Those 'aquatic apes' changed during the first million years: they evolved a bald body, blubber, large buoyant brain from marine DHA-fat, human nose, descended larynx and breath control for diving and speech, multipyramidal kidneys for excess salt, and all the other uniquely human traits.  

During the next 5 million years, I envision a population of 10,000 fat naked humans on Bioko. It was an easy life, mostly in the water, singing about turtles, sharing food—self-domesticating. It's rainy on Bioko, warm day and night, year round. They needed no clothes, tools, weapons, or fire.

Some early explorers (e.g. 'Homo Erectus', 'Neanderthals', and others) swam to the mainland. Most stayed on Bioko until about 200,000 years ago, when they used a Pleistocene land bridge to walk over. They invented clothes, weapons, and fire, needed to survive in all other environments.  

Allan Krill, Ph.D.
        Read Krill's Anthropogeny blog for details.        See also AquaticApe.net   



Mitochondrial DNA (maternal lineage) seems to point to western and central Africa

Allan Krill
 

As I posted last week, Y-DNA (paternal lineage, Haplogroup A00) seems to point to western Africa, near Bioko.

Mitochondrial DNA (maternal lineage, Haplogroup L1) seems to point to more or less the same part of Africa:

Human expansion: Bioko --> west Africa --> all parts of planet Earth.
(With the large brain, evolved due to marine DHA, Homo sapiens could go anywhere.) 

https://thereaderwiki.com/en/Haplogroup_L1_(mtDNA)


An estimated 10,000 Homo sapiens might have lived on Bioko Island for 5 My

Allan Krill
 

Many female sea-turtles come to the Bioko beaches each night during much of the year, to bury their eggs in the sand (Butynski 1996Tomas 1999). The turtles return immediately to the sea, leaving the eggs unguarded. The eggs are about the size of hen's eggs, and there are about 100 eggs in a typical nest. 

There are several species of sea-turtle that lay eggs on Bioko. They are huge animals, weighing several hundred kilos each. As recently as 1990, about 10 sea-turtles were being caught each night, and the meat transported by boat to city markets for sale. That corresponds to over a kilogram of meat daily for 1,000 people. Local people told researchers that in the 1940s, as many as 100 turtles were taken each night. The turtles are only taken along the 19 km of beaches on the southern side of Bioko (see the map), where there are no roads. Other beaches of the island are more accessible, and sea-turtle eggs there were overexploited in previous times, so that few if any turtles visit those beaches now. 

I think that these sea-turtles were important in human evolution. In my version of the aquatic ape hypothesis (Krill 2020) a few chimpanzees became trapped on Bioko, and their descendants evolved all the human traits. Those semiaquatic humans could have lived largely on sea-turtle meat, supplemented by shellfish and seaweed. Turtles are easy to kill without weapons, and the meat can be shared and eaten raw without tools or fire. If the Bioko humans were careful not to overexploit eggs, they could have taken as many full grown sea-turtles as they needed. 

There could have been a stable population of 10,000 semiaquatic humans on Bioko. This estimate is based on the 34 km of suitable beaches on Bioko (as mentioned in Butynski 1996), and an average of 300 humans per kilometer of beach. This estimate is obviously only a guess. At times there could have been many fewer, or many more. By being spread around the 200 km long coastline of Bioko, the semiaquatic human population would have been robust for millions of years, able to survive local viruses and volcanic eruptions. 

If my estimate of 10,000 semiaquatic humans seems high, consider the population densities of the emperor penguin on Antarctica, or the marine iguana on Galapagos. They also get their food from the sea. There are about 300,000 marine iguanas living along the Galapagos shorelines, with as many as 8,000 per linear kilometer (Wikipedia). Like the postulated chimpanzees on Bioko, the originally arboreal iguana became trapped on a volcanic island with no large predators and no terrestrial foods, and they were forced into a semiaquatic lifestyle. 

Based on molecular clocks, it is thought that human and chimpanzee lineages diverged about 6 my ago. If the founding chimpanzees became trapped on Proto-Bioko at that time, it might have taken a million years for them to evolve human traits and become modern Homo sapiens. After that, a stable population of 10,000 of these semiaquatic humans may have existed on Bioko coasts for 5 My, without needing to invent fire, weapons, clothing, or tools, and without leaving a fossil record. They would have spent the days in the water, singing and talking. They could have taught their children to respect turtle eggs and help turtle hatchlings reach the sea safely (something that sea-turtle mothers do not do.) 

Some humans may have left Bioko early. But unaware that large predators existed on the mainland, and having no weapons, few of them would have survived the first week away from Bioko. As recently as 200,000 years ago, most of the humans on Earth may have been living in the sea on Bioko.  

Butynski 1996: https://www.semanticscholar.org/paper/Marine-turtles-on-Bioko-Island%2C-Equatorial-Guinea-Butynski/280b23a019a94c2005e934a6c807e1eb033a0a1c

Tomas 1999:  https://www.researchgate.net/publication/277006928_Sea_Turtles_in_the_South_of_Bioko_Island_Equatorial_Guinea/link/559e3e0708aeb45d171602c0/download


World Map of Y-DNA Haplogroups

Allan Krill
 
Edited

I had no idea where in Africa geneticists thought 'Y-Chromosomal Adam' was from, but obviously I was pleased to discover this MAP of haplogroups and languages. It includes the recognition of Haplogroup A00, which was first published in 2013. I would call A00 reliable evidence, in contrast to one-time fossils finds, which may be false. More A00 genetic evidence has been independently determined by others since 2013.

This map is especially nice, because it shows languages and is not cluttered up with age estimates.

Old age estimates of A00 in the 2013 article were corrected by competitors in a publication in 2014. This type of correction is not usually possible with fossil interpretations, because competitors are not allowed access to the fossils or fossil locations.



The Khoisan people, who have a high frequency of Haplogroup A2,A3, also have genes that promote a unique amount of blubber (https://en.wikipedia.org/wiki/Steatopygia) which would be of value to aquatic apes, and not especially useful for terrestrial or arboreal ones. 

Khoisan people also have
 genes for elongated labia (female genitalia) that might have somehow helped women living in water avoid infections. 


Khoisan are thought to have the world's oldest language. It is characterized by click-sounds. 
Maybe aquatic humans on Bioko spent most of their time singing and click-talking in the water.  

I think chimpanzees became isolated on Proto-Bioko 6 my ago. After only one generation they were probably bipedal and pretty good swimmers. Evolution would go fast due to the extreme aquatic selection pressures. Most babies would likely drown soon after birth, and a new baby, maybe wth more human-like features (such as better nose and more blubber) could be born quickly to the same mother. After 100 generations (2000 years) the semiaquatic Bioko-apes would be so evolved that no one would call them 'chimpanzees'. After a million years, they were probably fully human (semiaquatic.) But we have no fossils of them. And any humans that left the island during the first few million years were quickly killed by predators.

If Khoisan have been on their continent for the past 200,000 years and North Americans have been on their continent for the past 20,000 years, that difference is trivial compared to the 5,000,000 years of humans in the water on Bioko. But Khoisan (in their genes, anatomy, physiology, and language) would be closer to the semiaquatic humans than North Americans are. So in my opinion, no living humans are significantly closer to chimpanzees. 

 


Aquatic humans on Bioko Island presumably had neutral-colored skin

Allan Krill
 

In the Bioko model of human evolution, human skin evolved from neutral-colored chimpanzee skin. The aquatic apes lost their fur and evolved into naked humans, because they were mostly in the water, at least during daylight hours. Water covered most of their bodies, and hair covered the tops of their heads.

Humans with neutral-colored skin presumably left Bioko during the last 300,000 years, when there were 3 or 4 periods of land bridges. The last humans may have left as recently as 50,000 years ago. They quickly invented clothing for protection during the day and warmth at night, but there was still some skin exposed to the elements. Their skin colors evolved according to where they migrated.

Lighter skin was selected for in Europe and Asia, because it helped convert the UV of sunlight to vitamin D. Darker skin was selected for in sunny African climates, because it helped protect against too much UV, which causes skin cancer.

Here is a map of the world showing UV levels. Note that the African coast in the Gulf of Guinea is relatively light, because it is often cloudy there. Bioko itself is not shown on this map, but it would probably be one of the lightest colors, because it has its own landscape and climate. Wikipedia: Bioko has a rather debilitating climate. The so-called dry season lasts from November to March, and the rest of the year is rainy. The average annual temperature of about 77 °F (25 °C) varies little throughout the year. Afternoon temperatures reach the high 80s °F (low 30s °C) and drop to only about 70 °F (21.1 °C) at night. Most of the time the sky is cloudy and overcast.


How early might apes have rafted to Proto-Bioko ?

Allan Krill
 

We don't know how old Bioko Island actually is, or when the ancestors of humans might have rafted there.

The oldest known rocks on the surface of Bioko are about 1 million years old (see Figures 1 and 3 from Fitton). But rocks at deeper levels are certainly older (see the cross section of a typical volcano, with some possible age numbers added). Bioko may be as old as its volcanic neighbors Oku (at least 23 Myr old) and Principe (at least 30 Myr old). (See the paper by J. G. Fitton, 1987).

Viruses, parasites, and their DNA vary from place to place. We will eventually be able to use the absence of 'African' DNA in living humans to know if and when human ancestors were not in Africa. (Negative evidence.) We will also be able to use DNA in living humans to determine where human ancestors actually were during different times (Positive evidence.) An isolated island like Bioko (during times with no land bridge) would have endemic parasites and viruses that might be identifiable in modern humans' DNA.

 


Is Bioko Island on 'The Wrong Side of Africa'?

Allan Krill
 
Edited

It depends if you are interested in where apes and humans could easily survive, or where bones and fossils could easily survive.

All African apes live in the green rainforest areas. Billions of mammals have lived or evolved in those rainforest areas, but not a single ape or mammal fossil has ever been found there. Bones decay quickly in those areas, so they do not become fossils.

If your career is to find and publish fossils, you can ignore the green areas. But if you want to understand apes and humans and their evolution, I think you should focus on the genetics (not the fossils) of apes and humans. 

(Bioko is an exotic volcanic island in the green rainforest area.)

Maps from Jonathan Kingdon (2013): Mammals of Africa, Bloomsbury Publ., 3763 p.


Out of Bioko theory of human evolution

Allan Krill
 

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".
http://AquaticApe.net


Beware of parsimony

Allan Krill
 

Beware of parsimony: it can kill a wonderful adventure story — reducing it to a single sentence. 

For example: Some chimps got isolated in an aquatic habitat on a barren volcanic island, and a few descendants escaped to leave early fossils, while others evolved further into humans, before spreading out around the world.

That simple model can explain all the evidence: human anatomy, physiology, paleontology, genetics, psychology (self-domestication), history. No one likes it, because it would kill many good adventure stories and many good careers.


Densely populated aquatic humans on Bioko would evolve and self domesticate

Allan Krill
 
Edited

AAT message #70636   Thanks for discussing perceived problems with Bioko. It helps me to consider these things.

 

The aquatic humans didn't have boats, so I'm not sure that a wide continental shelf would have been important. I think what is important that the aquatic habitat stayed unchanged and the food supply stayed reliable for the last few million years, while the sea level was rising and falling by as much as 120 meters. 

 

The southwest side of Bioko currently has beaches with a steady supply of huge sea-turtles and turtle eggs. The sand on beaches typically stays in the surf zone, moving up and down as sea levels rise and fall over geologic time. The aquatic humans did not need much space. They could have been packed densely along the shoreline, like Emperor penguins, or Crabeater seals (there maybe 75 million of them!), or the Marine iguanas of Galapagos. 

 

This is how densely the Marine iguanas can live: 

On some shorelines they can be very numerous, with densities as high as 8,000 per kilometer, and their biomass compared to the area they occupy may surpass that of any known reptile. However, their distribution is patchy, and colonies are generally found within 100 m of the ocean, naturally limiting their range. The total population for the entire archipelago is estimated to be 200,000–300,000 individuals 

 

With this kind of dense population and fat easy living on Bioko, the aquatic humans would self-domesticate. They would develop language and civilized behavior. They would share genes and evolve aquatic traits together, unlike clusters of undomesticated humans or hunter-gatherers spread around several continents.

 

Here is a map to show Bioko the last time it had a land bridge (from about 70,000 to 10,000 years ago). I think the last 'aquatic apes' (fully evolved Homo sapiens) may have left Bioko only about 50,000 years ago.


Anthropogeny. Inferring a two-step origin of the naked ape

Allan Krill
 

Manuscript in preparation. April 10, 2021


Out of Africa: origins and evolution of human malaria parasites

Allan Krill
 

Humans apparently first got malaria parasites by being bitten by mosquitos that had also bitten western gorillas.
Loy et al. 2017.
Out of Africa: origins and evolution of the human malaria parasites Plasmodium falciparum and Plasmodium vivax

That species of gorilla is nearest to the island of Bioko. Using DNA of parasites, viruses, etc., the origin of humans on Bioko is a testable hypothesis, not an unprovable model. When geneticists become aware of this hypothesis, they will begin actively testing it. 

Here is an interesting paragraph from that paper: 

Whilst it could be argued that the ape P. vivax was brought to Africa by humans who migrated from Asia (Prugnolle et al., 2013), this hypothesis has been refuted by sequences indicating the existence of a related, but distinct, Plasmodium sp. that also infects African apes. This Plasmodium sp. which is apparent in trees of mt, nuclear and apicoplast sequences (Fig. 4), has been found in chimpanzees from two different locations in Cameroon (the BQ and DG field sites in Fig. 2) and represents the closest known relative of P. vivax. The most parsimonious interpretation of this finding is that the common ancestor of these two species was in Africa, indicating that the lineage existed there for a long time before P. vivax arose as a distinct species (Fig. 4). We propose to designate this newly described species Plasmodium carteri, in honour of Richard Carter, who has long championed the hypothesis that P. vivax originated in Africa (Carter, 2003; Culleton and Carter, 2012).


Parsimony is popular among geneticists, unpopular among paleoanthropologists

Allan Krill
 

The parsimony principle is basic to all science and tells us to choose the simplest scientific explanation that fits the evidence. In terms of tree-building, that means that, all other things being equal, the best hypothesis is the one that requires the fewest evolutionary changes.

https://evolution.berkeley.edu/evolibrary/article/phylogenetics_08

It seems to me that paleoanthropologists do not prioritize parsimony, because complicated models help them to publish more scientific papers based on their paltry fossil evidence. They are trying to make complicated stories from minimal evidence. Their evidence is irreproducible and untestable by impartial scientists. Geneticists are looking for parsimony, because their evidence is so vast. They are trying to make simple stories, from a huge amount of evidence. Their models are mathematical and can be recalculated. If their models are not parsimonious, competitors will produce better, more parsimonious models. 

Here is a paper from 2013 that I just came across a few days ago, by Prado-Martinez et al. Great ape genetic diversity and population history https://www.nature.com/articles/nature12228

A parsimonious explanation is that orangutans, gorillas, and chimpanzees evolved and speciated just where we find them today (my additions to the chart in red). A parsimonious model is that humans are simply another species of Pan, that evolved within the same range as the modern chimpanzees, before humans began to make tools, weapons, clothes, and shoes, and wander into other ranges and habitats. As humans wandered beyond their site of speciation, they left some fossils in various places, but those fossils do not indicate where they actually evolved. 


The Passionate Ape, 2001 by Craig Hagstrom (pdf version)

Allan Krill
 

This is a brilliant book. Free pdf download here: PassionateApe.com

The Passionate Ape. Bad Sex. Strong Love, and Human Evolution
. by Craig Hagstrom.
Starting from the Aquatic Ape hypothesis, this work outlines the selective pressures and processes which could move an ape from land to an aquatic life and back.  Using primate morphology, it shows why apes make poor aquatics that are prime candidates to return to land when conditions permit.

It uses Great Ape behavioral traits to describe the mental constraints on such evolutionary moves, and to show how the land-water-land transition would in turn shape our mental evolution.  The major focus is on mating issues and sexual dysfunctions caused by these transitions, and how our coping mechanisms became vital assets setting us apart from the other Great Apes.


The past 12 months of Krill's messages at AAT@groups.io

Allan Krill
 
Edited

I have learned a lot from reading and writing messages with the AAT (aquatic ape theory) group @groups.io.
https://groups.io/g/AAT/search?q=posterid:4444723
I hope to get a group discussion going here some day at anthropogeny@groups.io


A volcanic-island model for the origin of the seal and other marine mammals

Allan Krill
 

From genetic evidence it is thought that the first seals evolved about 23 million years ago, near the beginning of the Miocene epoch. A simple model for the evolution of seals is that mammals resembling dogs, bears, and weasels accidentally rafted to oceanic volcanic islands that eventually sank out of sight. 

Erosion acts on rocks that are exposed above sea level. After the last active volcano of an oceanic island becomes extinct, erosion can remove the mountain and reduce it to a low flat-topped island. Erosion mostly stops at sea-level, but subsidence continues. Cooling and contraction of the mantle beneath the ocean floor cause oceanic islands to sink a thousand or more meters over a time span of tens of millions of years. A flat-topped undersea mountain is called a guyot, and there are 283 known guyots in the world's oceans. 

Considering the models for the Galapagos marine iguana, and for Bioko chimps, this model of sinking oceanic volcanic islands seems likely for seals, and for other aquatic mammals. But I have not found mention of such models on the internet. 


Anthropogeny. Inferring a two-step origin of the naked ape

Allan Krill
 

Manuscript in preparation.
March 9, 2021.


Where did the naked ape actually evolve?

Allan Krill
 

Manuscript in preparation. 
March 1, 2021


The Parsimonious Human Body Factory (PaHuB factory) was probably located on Bioko Island

Allan Krill
 

Boeing airplanes have crashed a few places in the world during the past century. Before crashing, those planes may have been modified in different cities, giving them new seats and paint jobs. But the planes really evolved and were produced at the Boeing factory and airport in Seattle. It takes a dedicated location with all the right conditions and materials to produce a commercial airplane. 

To evolve a human body from a chimpanzee-like ancestor, it must have required special materials (especially marine omega-3 fatty acids for exceptional brain evolution) and safe, reproductively-isolated conditions over a long time span. Humans are unique primates: they are bipedal, have bald bodies, large brains, protruding noses, blubber, descended larynxes, multi-pyramidal kidneys, and many other unique features that can best be explained by semiaquatic evolution.

I think that human bodies only evolved on the shores of Bioko Island, and only over the past 6 million years or so. Read this published article for more details. Bioko is an isolated volcanic island, near the places in Africa where chimpanzees and gorillas evolved. None of them left a single fossil, because the ground is wet and warm. All the bones decayed. No mammal fossils of any kind are known from those places.

Bioko Island is 32 kilometers from mainland Africa. 
The first apes to accidentally raft from Africa to Bioko could not swim. Their descendants might have been isolated on the island for millions of years. Bioko Island probably had no large predators or African viruses for millions of years. Its 150 kilometer coastline probably had an enormous supply of omega-3-rich sea-turtle eggs, as it does today. 

Mainland Africa is visible from Bioko, and it is a swimmable distance for an aquatic ape. (The water is warm.) After evolving bodies on Bioko, some of the unique semiaquatic primates could have dispersed to mainland Africa and other continents. Their bodies were slightly modified in those places, and only a few crashed in ways that could leave fossils.

If Homo erectus really existed, it was probably a late-model (produced about 1.5 million years ago) that walked from Bioko to Africa when sea level was temporarily low, during one of the glacial maxima. Erectus had a big enough brain to invent the clothing, weapons, and tools that were needed to survive as a vulnerable naked ape in Africa. (Naked humans with no clothing, tools, weapons, or fire could easily survive on Bioko beaches today. There no large predators, most days are cloudy, and the nights are never cold. Sea-turtle eggs from the hundreds of nests on beaches would be the main diet.)

Erectus is thought to have dispersed widely, leaving bones and chipped stones in East Africa, Europe, Java, and China. Neanderthals and Denisovans are fully evolved humans. They probably also came from the same PaHuB factory, with some minor modifications elsewhere.

DNA provides a sort of serial number, that can be read on living chimpanzees and humans. It is now becoming possible to find some of these serial numbers on crash fragments (fossils.) It may eventually be possible to determine if humans actually evolved on Bioko Island. An example of such evidence would be if all living humans carry an endogenous retrovirus (ERV) that is otherwise only found in animals living on Bioko.

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