Aquatic Mammals

Hawaiian monk seal

elephant seals

ringed seals

ribbon seal

Baikal seal

harp seals

hooded seals

spotted seals

Crabeater seals

Leopard seals

Ross seals

Weddell seals

harbor seals

Northern elephant seals

Southern elephant seals

Gray seals

Caspian seals

bearded seals

Mediterranean monk seals

Antarctic ice seals

Arctic ice seals

Sea creatures that start with L are:

• Lamprey (fish)
• Limpet (freshwater snail)
• Ling (fish)
• Lionfish
• Lobster
• Loggerhead turtle
• Lungfish

There are a wide range of physiological traits in human beings that can be explained by an evolutionary period in human existence that involved a partial, complete and then semi-aquatic phase in human prehistory.

These features include:

Hairlessness

Streamlined body

Reduced sense of smell

Subcutaneous body fat

Bipedalism

Diving reflex

Exostoses

The Nose

Downward facing nostrils

Philtrum

Breath control

Speech

Salt Tears

Eccrine sweat skin glands

Large Sebaceous glands

Hymen

Vernix caseosa

New-born swim ability

Webbed fingers and toes

Lunar Menstruation cycle

Lowest blood cell count of the apes

Highest haemoglobin per cell of the apes

Seafood diet bias

The aquatic ape hypothesis (AAH), sometimes referred to as the aquatic ape theory, asserts that wading, swimming and diving for food exerted a strong evolutionary effect on the ancestors of the genus Homo which is in part responsible for the split between the common ancestors of humans and other great apes. The AAH attempts to explain the large number of physical differences between humans and other apes in terms of the environment, methods of feeding and types of food of early hominids living in coastal and river regions.

As compared to their nearest living relatives, the great apes, humans exhibit many significant differences in anatomy and physiology, including bipedalism, almost hairless skin like some marine mammals, hair growth patterns following water flow-lines, increased subcutaneous fat for insulation, descended larynx, vernix caseosa, a hooded nose and the philtrum preventing water from entering the nostrils, voluntary breath control like marine mammals and birds, and greasy skin with an abundance of sebaceous glands, which can be interpreted as a waterproofing device. It has also been suggested that the abundance of docosahexaenoic acid in seafood would have been helpful in the development of a large brain.

There are several variants on the broad theme that early or proto-humans lived in close proximity to water, gathering much of their food in or near shallow bodies of water and developing and adapting new modes of locomotion in order to move and gather food (possibly including wading, swimming, and diving). Proponents have disagreed on the relative importance of fresh water versus coastal salt- or brackish-water habitats. Although the earliest proponents argued for an early (Miocene, about 6 million years ago) timescale, most now favour the view that the critical period of close association with waterside habitats was much later, Pleistocene or possibly late Pliocene (i.e., less than 2 million years ago). Possibly it happened when our ancestral Homo population spread along the South Asian coasts (so-called Out of Africa 1) where during the Ice Ages the lowered sea levels exposed large areas of the continental shelves; shell and crayfish were easily procurable by a dextrous, tool-using, thick-enameled, omnivorous primate and contained poly-unsaturated fatty acids such as DHA that were essential to brain growth. This may explain why this seaside phase (100-120 metres below sea level now) did not leave many traces in the fossil and archaeological record. From the coasts their descendants might have trekked into the continents along lakes and rivers.

Sometime prior to 546 BCE, the Milesian philosopher Anaximander proposed that mankind had sprung from an aquatic species of animal. He thought that the extended infancy of humans could not have originally permitted survival as a land-based species. This idea was based on elemental forces of mutation rather than natural selection.

The German biologist Max Westenhöfer was perhaps the first to publish the idea in an evolutionary context, writing in 1942 that "The postulation of an aquatic mode of life during an early stage of human evolution is a tenable hypothesis, for which further inquiry may produce additional supporting evidence."

The similarity of the subcutaneous fat in aquatic birds and larger aquatic mammals to the fat in humans had already been noticed by marine biologist, Sir Alister Hardy in 1930, while reading Frederic Wood Jones' Man's Place among the Mammals, which included the question of why humans, unlike all other land mammals, had fat attached to their skin. Hardy realised that this trait sounded like the blubber of marine mammals, and began to suspect that humans had ancestors more aquatic than previously imagined. Because it was outside his field and aware of the controversy it would cause, Hardy delayed reporting his theory. After he had become a respected academic, Hardy finally voiced his thoughts in a speech to the British Sub-Aqua Club in Brighton on 5 March 1960.

News of Hardy's speech generated immediate controversy in the field of paleoanthropology, and Hardy followed up by publishing two articles in the scientific magazine New Scientist. In the article of 17 March 1960 Hardy defined his idea: "My thesis is that a branch of this primitive ape-stock was forced by competition from life in the trees to feed on the sea-shores and to hunt for food, shell fish, sea-urchins etc., in the shallow waters off the coast. I suppose that they were forced into the water just as we have seen happen in so many other groups of terrestrial animals. I am imagining this happening in the warmer parts of the world, in the tropical seas where Man could stand being in the water for relatively long periods, that is, several hours at a stretch." (Hardy 1960:642) Despite receiving some positive feedback in the Letters pages of New Scientist in the weeks that followed, and strong backing from a professor of geography, the idea was largely ignored by the scientific community.

In 1967, the hypothesis was positively reviewed in The Naked Ape, a book by Desmond Morris in which can be found the first use of the term "aquatic ape" (Morris 1967:29). Writer Elaine Morgan read about the idea in Morris' book and was struck by its potential explanatory power. She developed and promoted it over the next thirty years, publishing six books on the subject. Several other proponents have published work in favour of the aquatic ape hypothesis during this time including the physician Marc Verhaegen, neurochemists Michael Crawford and Stephen Cunnane, and ecologist Derek Ellis.

The hypothesis and its variations have been largely ignored by mainstream paleoanthropology, although occasional papers have criticised certain aspects of it. It has been suggested, for example, that a broad terrestrial diet would ensure sufficient access to docosahexaenoic acid that there was no requirement for high consumption of seafood and accordingly no reason to posit an aquatic phase in human evolution for dietary reasons.

In 1991 a symposium was held in Valkenburg, Holland, titled "Aquatic Ape: Fact or fiction?", which published its proceedings. The chief editor, Vernon Reynolds, rejected the strong version of the hypothesis, but accepted a weaker form, summarizing that "overall, it will be clear that I do not think it would be correct to designate our early hominid ancestors as 'aquatic'. But at the same time there does seem to be evidence that not only did they take to the water from time to time but that the water (and by this I mean inland lakes and rivers) was a habitat that provided enough extra food to count as an agency for selection. As a result, we humans today have the ability to learn to swim without too much difficulty, to dive, and to enjoy occasional recourse to the water."

Despite the conciliatory wording of the summary, and the fact that half of the submitted papers were in favour of the hypothesis, it was reported in the anthropological press that the hypothesis had been rejected.

However there has since been some acceptance. In 2004 Colin Groves, Professor of Biological Anthropology at the Australian National University in Canberra, Australia with co-author David W. Cameron stated that

"..nor can we exclude the Aquatic Ape Hypothesis (AAH). Elaine Morgan has long argued that many aspects of human anatomy are best explained as a legacy of a semiaquatic phase in the proto-human trajectory, and this includes upright posture to cope with increased water depth as our ancestors foraged farther and further from the lake or seashore. At first, this idea was simply ignored as grotesque, and perhaps as unworthy of discussion because proposed by an amateur. But Morgan's latest arguments have reached a sophistication that simply demands to be taken seriously (Morgan 1990, 1997). And although the authors shy away from more speculative reconstructions in favour of phylogenetic scenarios, we insist that the AAH take its place in the battery of possible functional scenarios for hominin divergence."

Humans are the only terrestrial animals that can voluntarily hold their breath at will.

The ability to hold and control breath is necessary for complex speech. This ability would, of course, also be needed for diving. It is likely that the ability of humans and aquatic mammals to hold their breath was an adaptation meant for diving, and that the development of complex speech was a side effect.

Also, humans have a descended larynx, which other apes do not. This allows us to gulp large amounts of air. Most animals only breathe through the nose, but the descended larynx allows humans to breather through our mouths, which allowed us to take deep breaths "prior to diving" (Watson). The larynx thus allowed early humans to spend longer periods of time underwater than they could have if they were taking shallow breaths through their noses. Complex speech is also dependent on the descended larynx. Other aquatic mammals, such as sea lions, walruses, and manatees have descended larynxes.

There is another similarity between humans and aquatic mammals: the diving reflex, also known as bradycardia, a decrease in heart rate and redistribution of blood to the brain and the organs. This is a natural reaction of humans to being submerged. Other apes do not share this ability, as they obviously have no use for it. "Humans can dive to depths of one hundred meters at the extreme but most humans can certainly dive to ten meters," which no ape would do (Watson). The diving reflex makes swimming and diving practical, and humans have no living ancestors that possess this trait. It must have been acquired at some point after humans split from apes, and this supports the idea that man evolved in an aquatic or semi-aquatic environment.

• The pattern of hair on our backs. Like all mammals, humans are covered with short hair. The hair on our backs lays down and towards the center in a streamlined way that would theoretically facilitate swimming.
• Noses. Compared to all other primates our noses are very long and rigid. Our nostrils point down as opposed to gorillas and chimps whose nostrils are almost flush with the face. This is quite useful when swimming for preventing water from getting into the respiratory system.
• Geological evidence. At around the time that Homo sapiens became a species in their own right, sea levels appear to have been higher than they are now in the areas where human fossil evidence is being found.
• Swimming primates. Most primates cannot swim and do not like water. (If I remember correctly, chimps sink like rocks.) One exception is the Probosis monkey which has been seen wading bipedally in waist-deep water. Probosis monkeys have developed longer legs than many primates, and their proportions appear closer to humans than most other monkeys. Humans, however, love water. Look at the modern world and how cities and vacation spots are arranged. Few seem interested in touring savannahs, but we flock to beaches.

• Voluntary breath control. Primates are physiologically unable to hold their breath. However, humans have developed the ability to regulate their own breathing, a necessity for diving.
• Vocalization. The wide range of sounds we can make is due to the orientation of our larnyx. We share this feature with only a few other animals: the dugong, sea lion, and walrus.

• The sensitivity and dexterity of our hands is perfect for searching for food underwater. Our fingernails are stiff and fast-growing, and therefore ideal for prising open shellfish.
• Our tool-making ability. Pebbles are perfect for opening shellfish, as otters have similarly discovered.
• When swimming, all signalling becomes useless apart from vocal signals. If we developed language for the purpose of hunting on land, it would be more useful to create a sign language; hunting is usually a very quiet activity. Other creatures with a highly developed vocal 'language' include whales and dolphins, not creatures such as wolves.
• Of all similar creatures, the elephant is the most striking. Its evolution is really quite remarkable - it is descended from a small pig-like animal, but then over the ages, grew to be the largest land animal in its era. It is very easy to compare it to another mammal whose size swelled remarkably over the ages: the whale. In water, large mass is not the problem it is on land. Indeed, it is a benefit, as larger creatures lose heat much more slowly.
• Its anscestors also had peculiar tusks. Some had spade-shaped ones, perfect for digging in soft, waterlogged soil, but not much good in the plains.
• The early ancestors of the elephants showed a movement of the nose towards the top of the head. This would have been uncalled for on land, but excellent in the water. Nowadays, of course, they have a trunk. And what use is a trunk? It's inefficient for grass eating (a long neck would be better), and unnecessary for tree browsing. But it makes a pretty good snorkel. Not to mention its use for picking water plants.

Suggestion that Pachyderms all shared a more intense evolutionary period with us and the sea. The Seal, Dugong and Walrus quite obviously going the way of the Dolphin, although there is no reason why time and the environment should not leave them where they are or move them in the direction of the land once more.

The Hippopotamus still living a semi-aquatic existence, whilst a distant relative went all the way and became the Blue Whale, fully aquatic and the largest animal to have ever lived as far as we know.

The Elephant, Tapir (both of whom have trunks [read:Snorkel] which have been shown in prehistoric times to have been moving towards the top of the skull, clearly an advantage in the water) and Rhino also share with the other Pachyderms the hairlessness seen in humans and share numerous other similarities not seen in non-aquatic or semi-aquatic mammals.

Elephants by way of interest also have webbed feet although this has atrophied as in humans. They can also swim for six hours straight and their large size is in anycase probably attributable to a long period of permanent water habitation. Elephants also show the crying response when emotional. Hardly any land creatures cry and hardly any sea creatures don't. They are also highly intelligent and have a complex language which includes Infrasound comunnication.

• subcutaneous body fat, similar to aquatic mammals'
• ability of new-born babies to swim
• diving reflex: our breathing slows down underwater
• hairlessness, except on head, that hair floating for infants to hang on to
• long-chain fatty acids composing the brain easily derived from marine food, not easily from Savannah food
• crying salt tears
• resonant voice
• upright posture, bipedalism
• people with their hips together resemble dugongs in streamlining effect
• webbing between fingers

The Aquatic Ape Theory is at least a reasonable hypothesis, if not a fully acceptable scientific theory. It provides a sensible explanation for why human beings, while genetically similar to apes, possess so many different physical features, and how these physical adaptations could have come into being. Without the Aquatic Ape Theory, it is hard to explain the parallels between humans and aquatic mammals. Science, especially evolutionary biology, is a constantly changing field. Nothing is set in stone. The AAT may someday replace the "Savannah theory of human evolution" which most evolutionary biologists now deny they ever supported which is telling, especially since this coincided with the discovery that the whole basis for the so-called "Savannah theory" was incorrect and the environment which produced upright man was wet and wooded.

Perhaps a third theory will arise. At the very least, Elaine Morgan's books have made some scientists rethink what they have been taught about evolution.