Wikipedia and the scientific community
Fingers, hands, feet and toes
In January 2013 scientists discovered a possible explanation for why the skin on human fingers and toes shrivels up like an old prune when we soak in the bath. Laboratory tests confirmed that wrinkly fingers improve our grip on wet or submerged objects, probably working to channel away the water like the rain treads in car tires. It is often wrongly assumed that wrinkling is the result of water passing into the outer layer of the skin and making it swell up, but researchers have known since the 1930s that the effect does not occur when there is nerve damage in the fingers. This shows that the change is an involuntary reaction by the body's autonomic nervous system — the system that also controls breathing, heart rate and perspiration. In fact, the distinctive wrinkling is caused by blood vessels constricting below the skin.
Back in 2011 Mark Changizi, an evolutionary neurobiologist at 2AI Labs in Boise, Idaho, had suggested that the purpose for wrinkly fingers and toes might have an evolutionary function and the latest experiments have shown that wrinkly fingers do in fact help test subjects grip wet objects far more effectively than dry objects (for which there is no noticeable difference).
"We have shown that wrinkled fingers give a better grip in wet conditions — it could be working like treads on your car tires, which allow more of the tire to be in contact with the road and gives you a better grip," says Tom Smulders, an evolutionary biologist at Newcastle University, UK, and a co-author of the paper. Wrinkled fingers could have helped our ancestors to gather food from wet vegetation or streams, Smulders adds. The analogous effect in the toes could help us to get a better footing in the rain.  
Human hands are distinguished from apes by possessing longer thumbs relative to fingers,  and broader palms. It has been argued that this was an evolutionary response to our need for higher dexterity. However, galagos, lemurs etc. have even longer thumbs comparatively and they are not significantly "highly dextrous". Chimps do not have very long thumbs and yet they can easily pick up a needle from the ground.
Webbed fingers and toes
(This may have nothing or little to do with the 'Aquatic Ape Hypothesis' as such, but perhaps it is worth including for further research and/or debate.)
A rare condition in humans known as 'syndactyly' is the fusion of one or more digits on the hands or feet. Sometimes it is just the skin that is joined together, and sometimes the bones themselves are fused. Webbing is of course normal in many species of water-habitat birds, such as ducks; amphibians, such as frogs; and some mammals, such as kangaroos. Some terrestrial mammals such as dogs, cats and even cows, however, also have some webbing between their digits. Syndactyly in siamangs Symphalangus syndactylus (fusion of toes 3 and 4) perhaps evolved to provide a stronger grip on branches.
In humans syndactyly is considered unusual, occurring in approximately one in 2,000 to 2,500 live births. During early fetal development, all our toes and fingers are webbed together. At six to eight weeks, however, apoptosis takes place and an enzyme dissolves the tissue between the digits, causing the webbing to disappear. (This might be an indication of a much earlier evolutionary adaptation, between 400 and 350 million years ago, when shallow water vertebrates exchanged fins for forelimbs adapted to digging or walking). The exact cause of webbed fingers and toes in some humans today is unknown. It could be inherited, since family members often share the condition, but it is also common for only one member of a family to have webbed toes. 
These adaptations are treated as deformities or a mutations and surgery is usually offered to correct it.
Webbed hands and feet may provide some advantage to swimmers. Even the most fully aquatic mammals such as whales have similar hand and finger bones which are all that remain of their once terrestrial limbs. Their hind legs appear during fetal development but then disappear before birth.
Human beings have flat, arched soles, with short toes. They are quite different from the feet of other primates, which generally have much longer digits (toes) and an opposable big toe, which makes them quite suitable for grasping and climbing, like the hands. We have lost much of the use of our toes, for anything other than providing balance when we walk. Human feet are ideal for two things: walking on soft, wet, infirm terrain such as swampy mud, lake bottoms, sand and shingle (where hooved animals are more likely to sink or slip); and for swimming. Our flatter, moe 'paddle-like' feet are better able to provide thrust when we swim, yet they have not started to turn into flukes or flippers that fully aquatic animals have. Modern human swimmers or divers benefit greatly from the extra thrust provided when wearing artificial flippers or fins, but this is just an extension of what we already have. Anyone who has tried to walk on land in this equipment knows it is not practical, so our ancestors made a pay off between feet ideal for swimming and feet ideal for wading or walking on land.
Although the soles of our feet tend to harden over time when accustomed to going barefoot, they are still much more vulnerable to injury than thick padded paws of many carnivores, or the hard, narrow hooves of much of their prey. This suggests that our feet are not well adapted to running across the savannah or other hard surfaces, but very well adapted to a life spent wading and shallow-dive harvesting /fishing on the seashore or in rivers and lakes.
Of course, today, our feet are used for walking & running, but that doesn¹t mean that our foot evolved from a chimp-like foot for walking-running (a
Our foot¹s unexpectedly long and strong first and last digital rays are seen in swimmers (sealions, penguins) & perhaps waders (although these typically have more divergent digital rays), but cursorials have long and strong middle digital rays (e.g. 3 in equids, 3-4 in carnivores and artiodactyls, toe loss in ostriches & horses).
Our feet seem to have evolved from climbing- to swimming-feet (aquarboreal, later littoral) to wading-walking feet. Chimpanzee feet from climbing to aquarboreal to climbing-walking feet?
Homo or Australopithecus Naledi's forefeet resembled a modern human's - only a bit flatter and with more curved toes. The foot structure suggests the hominin waded or swam.
Cursorial bipedal animals such as ostriches have digitigrade feet with very robust and long central digital rays, whereas wading bipedal animals such as flamingoes have flatter feet with relatively longer first and last digital rays. This raises the question whether the flat human foot originally evolved for wading in very shallow waters, and only secondarily evolved for walking or running on terra firma.
In naledi the combination of flat and fully plantigrade feet (broadly similar to that of modern humans) with curved hand phalanges which might suggest a locomotion not unlike that of bonobos or lowland gorillas who occasionally or regularly wade in shallow forest swamps or wetlands for waterlilies or sedges, but more frequently. The strongly curved manual phalanges in combination with the gorilla-like pedal curvatures suggest they also frequently climbed in the branches above or near the swamp.
If naledi spent a lot of time in wetlands or forest swamps in considerable densities as seen in lowland gorillas collecting aquatic herbaceous vegetation in forest bais, this might possibly also explain their accumulation and fossilisation in mudstone, without having to assume deliberate burials in caves.
[Marc Verhaegen / AAT group]
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