Aquatic Ape Theory (AAT)
There is no doubt that Homo sapiens are
much different than any other animals living on the Earth.
We are a unique species in the animal kingdom. This is the
reason we have always considered ourselves special and above
other earthly beasts. For this reason, it is hard for people
to understand evolution. Even with our closest ancestors the
primates, they look very different in appearance. So what
happened? What happened to our ancestors millions of years
ago to set us on the course we are on today? Why do we walk
have relatively no hair? Why do humans get obese and sweat
extensively? Why is our Larynx descended so low that we can
choke on the very food that gives us life? These are some
of the questions the Aquatic Ape Theory (AAT) tries to explain.
Most of the classical theories about these anatomical anomalies
have major flaws and problems. Even the classic “Savanna Theory”
that had been accepted as fact has now been dismissed. The
Aquatic Ape Theory gives us fresh perspective and new possibilities
to some of the biggest mysteries about our origins.
The Aquatic Ape Theory states that approximately 6-7 million
years ago, our ape ancestors were trapped in a semi-aquatic
environment. This forced them to search for food in the water
and become very comfortable in the water; over time altering
their bodies to be more effective in the water. The theory
says that a founder population of apes got isolated on an
island-like setting when East Africa flooded. So if a population
got isolated, they would need to take to the sea for survival.
It took whales 50-60 million years to go from fully terrestrial
animals to fully adapted aquatic animals. Skeptics of Aquatic
Ape Theory insist that it would take 50-60 million years to
see changes in physiology of a transition to becoming aquatic.
The one thing that they do not understand is that AAT states
that a small population of apes became isolated. Evolution
acts much faster on small populations, so some changes could
have easily taken place in a million years. That is not to
say that we became mermaids with a whale-like tail, just that
we started the transition to becoming aquatic. Some of those
traits can still be seen today.
There are many facts that make this theory
very plausible. We know that 6-7 million years ago East Africa
flooded, creating many islands. This flooding lasted for around
a million years and is the same part of Africa where famous
fossils like “Lucy” have been found. We know that mutations
in small groups of populations can greatly speed up the evolutionary
process. This means that if a population got split off from
the founding population it could evolve more rapidly. We know
that as a result of becoming aquatic, terrestrial animals
generally will lose their hair, become more streamlined, and
retain blubber. Aquatic mammals all have blubber to help insulate
and create buoyancy. For instance, whales were once terrestrial,
but after millions of years they lost their legs became more
streamlined, lost their hair and replaced it with blubber.
Humans are the only terrestrial mammals that can consciously
hold their breath. Not even chimps or other primates can do
this. Having blubber or fat under your skin makes you more
buoyant in water. These are some of the facts that AAT is
Bipedalism has been
a mystery plaguing us for a long time. It is very hard to
understand why our ancestors started walking upright. Logically
it makes no sense. Quadrupedal organisms are clearly faster
at avoiding predators than bipeds. Our bodies are not made
to walk upright. Humans have back problems are because we
walk upright instead of on all fours. The spine is much better
supported on all fours. So if our ancestors started walking
upright because of chance mutations, nature did not select
for them to die out. So it must have provided an advantage
or been neutral possibly as an exadaptation (preadaptation).
Most conventional theories of why our ancestors starting walking
upright include: the ability to stand up and scan the horizon
for prey/predators; to carry things and use tools; and for
feeding behavior. There is another mammal that stands up to
look for danger and it is the meerkat. These little critters
have their own show on Animal Planet. When you watch them
they are constantly standing up on their hind legs to keep
a lookout. However, when they see danger they drop down and
run on all fours. In fact, no mammal that has adapted this
behavior has ever taken more than a half dozen steps on two
legs. If this theory was true it could account for an upright
posture, not for locomotion. Walking and running upright is
a lot different than just standing.
Carrying behavior was a very popular
concept. This is an older theory that said we needed to use
tools so our ancestors walked upright to free the hands. This
has been disproved because our ancestors were walking upright
before we ever used any tools. The other popular theory is
that they were carrying food home to their family. This was
a popular theory because people noticed that 1% of the time
chimps walk upright to carry food. The question is what food
were they carrying? Australopithecus afarensis diet consisted
of nuts and berries. They would have to be carried by the
handful and this would not have been worth all the trouble
to carry home. Modern chimps, when carrying a larger meal,
drag it behind them while walking on three legs. Some people
speculate that our ancestors might have needed to carry water
and food over long distances and it would be an advantage
to walk upright. However, people would have needed some kind
of container to carry water, and there is no evidence that
they would have any idea about doing this.
The theory that our ancestors walked upright for feeding is
a little outdated. Modern primates do not show any bipedal
behavior for foraging. Scientist watched wild chimpanzees
for over 700 hours. They noticed that 80% of the time that
the chimps stood up was for feeding behavior. So it seemed
the best theory. However, this fits in with the scanning the
theory. It might have been useful to stand to reach and get
food, but it would not in any way lead to Bipedalism. No scientists
agree solely on any one of these theories. Some people like
to pick and mix from these theories. But the underlying fact
is that something happened to our ancestors to make them start
walking upright. No other primate uses this form of locomotion
the way we do. The proboscis monkey lives in mangrove swamps
and has been observed in the wild walking upright in the water
from one feeding ground to another. This hasn’t led to the
proboscis monkey becoming a biped, but is interesting nonetheless.
Other apes, who are more closely related to us than monkeys,
also walk upright when wading in water.
The Aquatic Ape Theory attempts to answer
this question of Bipedalism. AAT says that our bodies started
becoming more streamlined as a result of natural selection.
This would have made our hips start to become narrower and
our bodies more slender. If a population had evolved for swimming
and diving, when the water receded, and they became more terrestrial,
it would have been easier for them to walk upright than to
go back to all fours. So AAT is suggesting that Bipedalism
is an exadaptation from becoming a more streamlined swimmer.
Another of the
main points of AAT is the fact that we are relatively naked
mammals. The only other mammals that are naked are aquatic
or underground, like whales, hippos, and naked mole rats.
These mammals lost their hair for various reasons. Aquatic
their fur for insulation and gained blubber to keep them warm.
Blubber is more effective in water than fur. Naked mole rats
lost their fur as a result of living underground.
This is a question that people have been trying to figure
out for quite some time. Most of the old theories have been
dismissed, but AAT gives a reasonable explanation. Some of
the old theories are: losing hair as a result of sexual selection,
a result from wearing clothes, and a result of nature selecting
animals that didn’t have hair where parasites could thrive.
The idea of wearing clothes to make us lose our fur is not
very credible because the odds of humans wearing clothes in
Africa where the temperature is very high, was not likely.
Even if we were wearing clothes it would not likely lead to
us losing our fur. Fur actually is a good adaptation to have
in Africa. That is why primates and other animals still have
fur. It is much more effective at cooling down the body than
sweating with no fur. This has been tested by shaving animals
and leaving them in the sun. They seemed to get hotter and
sweat more. You can even look at people today; they sweat
more when not wearing a shirt than when they wear one.
Sexual selection is another theory of why we might have lost
our hair, however, it is quite unlikely. The concept is that
chance mutations caused some early apes to lose their hair
and then females selected to mate with them. In reality if
this happened, they probably would not have mated with them
because it would have not been normal. As to losing our fur
because of parasites, you can look at modern primates. They
groom each other to get rid of these parasites. Why would
they not have evolved to lose their hair?
The obvious thing to do is to look
at other hairless mammals and see why they lost their hair.
Usually this is because of an environmental variable, like
being in the water or subterranean. So what AAT states is
that after a million years of selection for aquatic apes,
they eventually lost most of their hair. This is the most
reasonable explanation for why an organism would give up an
advantageous trait like having fur for a less adaptable trait.
People do have some hair but not fur. The hairs humans do
have, has a very peculiar orientation. Unlike other primates,
whose hairs all point down, the hairs on a human appear to
follow the direction of water flowing over the body. Hair
does seem to grow on other animals in relation to their life
style. Most animals have downward facing hair, as if to assist
in rain running off them. Animals like Camels that are not
as likely to be caught in the rain, have hair that sticks
out everywhere. Moles do not have hair because they need to
be able to move backwards through their tunnels so dirt does
not get engrained in the hair. So AAT provides a very good
reason for why our ancestors lost their hair.
Another question that AAT answers beautifully
is “Why are we so fat?” Of all the primates, we are certainly
the fattest. This fatness is not just because we have McDonalds
on ever corner. Some people are genetically predispositioned
for obesity. When we are born, we are already chubby. In fact,
it is our chubby cheeks that trigger parental protective processes.
Other primates like chimpanzee’s infants are generally skinny.
Rose Frisch stated that if a woman’s adipose tissue constitutes
less than 17% of her body weight, she ceases to menstruate
and cannot reproduce. Other mammals can reproduce with 2%.
So there must have been a selection for this. In fact humans
contain ten times as many adipocytes (fat cells) than would
be expected in an average mammal of similar size.
Because we didn’t inherit these traits from primates, AAT
looks at the only other animals that are liable to collect
fat in this way. They are hibernating animals and aquatic
animals. Nobody has yet to suggest that our ancestors slept
off the winter in hibernation. It is interesting that terrestrial
mammals tend to store fat around their internal organs whereas
aquatic mammals store their fat on the outside, near their
skin. Seals actually store 99% of their fat under the skin.
In the 1950’s, P.F. Scholander reported, after studying which
was a better insulator in water fur or fat, that fat was much
more effective as an insulator in the water than fur. What
is interesting is that humans have this same layer of subcutaneous
fat. We store it just as aquatic mammals do. The question
then, is if fur is a better insulator in air and fat is a
better insulator in the water, why would we be naked with
blubber? According to AAT this is simply because of our aquatic
Humans, unlike other mammals and primates,
are missing the panniculus carnosus. This is a cutaneous muscle
layer found throughout the skin in most mammals. It is the
twitching muscle that terrestrial animals use to get rid of
insects and dirt. All we have is a vestigial patch in the
neck. Perhaps our skin had too much fat in it and the muscles
could not work the same way and it gradually faded away. Or
perhaps the fact that we could jump in the water to avoid
the pests made it useless.
One of the best traits about humans is
our ability to communicate verbally to each other. Because
of this we became the species we are to day. We learned to
teach, and record history. The reason why we have the ability
to speak is because our larynx is descended past
our esophagus and we can consciously control our breathing.
Modern day chimpanzees, and most other mammals, cannot do
this because their larynx is not descended; instead they can
breathe while they eat. In fact, chimpanzees are mentally
capable of speech, however they cannot do this because of
their inability to consciously control their breath and they
do not have a descended larynx. Their brains have a Broca's
area that would enable them to speak, but they cannot physically
There would not be a logical reason for our larynx to drop
down. In fact it would be a disadvantage because of choking.
We cannot swallow and breathe at the same time. So really
the only explanation for it is for a need to speak. There
are a few reasons that it is unlikely that nature selected
for a descended larynx because of a need to communicate. You
could ask the question why any other primates did not develop
the same mechanism. Surely chimpanzees could benefit from
being able to speak. The problem is, that is not how evolution
works. It doesn’t try to find advantageous traits; it works
through a process of trial and error. A lot of times things
evolve as a result of other things and they are called exadaptations.
A good example is spongy bones in birds. The small dinosaurs,
that eventually gave rise to the birds, developed spongy bones
as a result of running from predators. So the lightweight
bones that helped the dinosaurs survive ended up being beneficial
to birds for flight. They did not evolve for the purpose of
flight, but they certainly helped it happen. AAT attempts
to answer this anomaly in a similar fashion. They say that
natural selection selected for these aquatic apes to be able
to come up for air. Breathing in air through your mouth is
much more effective than through your nose. So by being able
to come up for a big gulp of air would be more efficient than
trying to do this through the nose. The conscious control
of breathing would have come from this diving behavior. Then
millions of years later these seeming disadvantages on land
enabled us to be able to speak.
questionable problem about this idea is that there are so
few animals that have a descended larynx. However, the ones
that do have one are aquatic. The walrus and sea lion are
two examples that have this trait. Not all aquatic animals
have this function. Whales actually have a larynx that moved
up instead of down. The reason that this is significant is
because Homo sapiens are the only terrestrial animals that
have a descended larynx. Also, there is no advantage to mouth
breathing. In fact, it can lead to illness by not filtering
air through mucus in the nose; breathing in pathogens that
don’t get filtered out, and go right into the lungs. People
are also the only animals that can choke on their own vomit.
The descended larynx is also the cause of sleep apnea. So
if there are so many disadvantages to have a descended larynx,
why would nature not select for these animals that could choke
on their food? AAT is the best theory for this. There is not
any other theory that can stand up to it like AAT.
Another interesting aspect about our bodies
that makes us unique in the terrestrial world is our sweat
and tears. Humans, even with out exercise and in temperate
climates, have to drink more water than any other terrestrial
animal. Dehydration of 10% may be fatal to humans, whereas
most animals can go up to 20%. So we cannot go too far from
water in order to survive. Humans waste more water than any
other land animals on earth.
All primates and most land animals pant as a result of thermal
regulation. Humans are the only animals that seem to have
lost this ability. We pant when we exercise, but this is to
deliver oxygen to the lungs not to cool down. Our sweating
is how we cool down. We are one of the few animals that use
eccrine glands for cooling down. Other apes and animals have
these glands; however, they do not use them for cooling down.
In most mammals the eccrine glands are connected to hair follicles.
Humans no longer have these glands connected to the hair follicles,
however, we have many of them spread out through our skin
and they secrete sweat directly onto the skin. We also have
twice as many eccrine glands than other apes. One of the major
downfalls of this type of cooling is that it takes up to 20
minutes to activate. It is also a wasteful type of sweating
compared to the sweating of sheep and horses.
In it’s beginning AAT thought that perhaps these glands evolved
as a result of being in salt water all the time and having
excess salt in our bodies. This would sound logical to adapt
method of salt removal. However, it has been researched and
we have determined that it is not possible that we used sweat
and tears for salt removal. Sweating is essential to cooling
our bodies, but our kidneys do much of the work for salt removal.
But this does not mean that this excessive sweating matter
didn’t arise because of our aquatic past. Basically, if AAT
is true and it led to our Bipedalism and nakedness, when the
water receded and we became more terrestrial we would need
a new adaptation for cooling down our bodies. As a result,
our bodies would need to start producing more eccrine glands
to sweat and cool down. So indirectly we are such a leaky
animal because of our aquatic pasts.
There are many other oddities with the
human body that are interesting and worth mentioning. The
Dive reflex is common in many animals. When animals are submerged
in water, their heart rate slows down, and the blood supply
to the skin lessens so that organs that need oxygen can have
more available. This is fairly common in most animals from
ducks to humans. It is basically a survival reflex that the
body performs. In fact, sharks and fish do the same thing
when you take them out of the water. Aquatic animals show
this effect stronger than terrestrial animals. So over time
the dive reflex evolved to be stronger. They decided to do
a comparison test between humans and other animals. They concluded
that a well trained diver had the same dive reflex of a semi-aquatic
animal like a beaver or an otter.
Human noses are very interesting. It seems
to be designed for a person to dive into the water or swim
underwater without having water being forced into the nasal
passages. We know that the nasal spine didn’t start showing
in hominids until Home erectus about 2.5 million years ago.
It could be argued that the downward pointing nose didn’t
evolve until then. Fleshy appendages do not fossilize, so
if you saw the fossilized skull of an elephant, there would
be no way to tell that it had a trunk, unless you knew what
one looked like today. The same thing could have happened
with the nose. The aquatic environment could have selected
for a downward facing nose for swimming through water, and
then over time the boney structure formed for additional support.
Humans also have a strange embryological seam called a philtrum.
This is the little channel
that runs from your nose to your upper lip. No other primates
have this strange feature. Some people are able to close their
nostrils by pushing their upper lip up against their nose.
It actually fits perfectly. This can give you an advantage
underwater or when jumping into water to prevent water from
going into the nose.
Human Blood is very interesting. It is
known that aquatic mammals have a reduced number of blood
cells per unit volume. Chimps have an average of 7.3 million
red cells per cubic millimeter; gorillas have 6.3 million;
and humans have 5.1 million. Also in regards to the hemoglobin
that carry oxygen to the lungs, aquatics have a higher content
of hemoglobin per cell. Chimps have on average 12.2 per cell;
gorillas have 13.2 per cell; and humans have 18.6 on average.
The increase in hemoglobin for aquatic animals is very advantageous
for carrying more oxygen throughout the body. Perhaps the
reason we have an increased number is because of an aquatic
The Aquatic Ape Theory attempts to
answer a lot of unanswered questions that have plagued mankind
about our heritage. The answers may be speculative, but no
more than all of the other theories. The simple fact is that
we love the water and feel comfortable in it. Some women even
prefer to give birth in the water. We have swimming pools
and Jacuzzis for recreation in the water. People have always
been fascinated by the ocean and it has inspired some of the
greatest stories and adventures. 90% of all life on earth
evolved in the water, so is it unreasonable that our ancestors
might go back to the most abundant food source in the world,
the ocean? Something in our past changed us and put us on
a course to what we are today. Our ancestors started walking
upright on their hind legs becoming bipedal; the hair on their
bodies changed direction and they became naked; the larynx
descended; they became fatter; they forgot how to pant; they
gained more eccrine glands for sweating; their nostrils started
to point downward; and they learned to speak. The Aquatic
Ape Theory explains how all of these things could have happened.