Essay/Term paper: Homo aquaticus?

Essay, term paper, research paper:  Science Reports

Homo Aquaticus?


I. Introduction

When the human brain is compared with the brains of apes there are several
obvious differences; the centers for the sense of smell and foot control are
larger in apes than in humans, but the centers for hand control, airway control,
vocalization, language and thought are larger in humans. In my paper, I will
describe the most defined differences of brain size and centers between humans
and their closest relatives, chimpanzees, to compare them with other mammals and
to draw conclusions about the evolution history of humans.

II. Brain Evolution

Humans and chimpanzees are biochemically (DNA) and therefore probably
phylogenetically (evolution relationships), more alike than chimps and gorillas.
But the brains of chimps and humans differ in size and anatomy more than
gorillas and chimps. The brains of chimps and gorillas probably didn't go
through many evolutionary innovations, because they generally resemble other ape
and monkey brains. This implies that the human brain changed a lot after the
human/chimp evolution. With the exception of the olferactory bulb (scent), all
brain structures are larger in humans than in apes. The neocortex (part of the
cerebral cortex), for instance is over three times larger than in chimps, even
though chimps and humans are pretty close to equal in body weight.
Each side of the brain is diveded by the central sulces into independant
halves. Just before the central sulcus lies the post-central cortex, where the
opposite body half (right side for left brain, left side for right brain). Just
in front of the central sulcus lies the pre-central cortex where the information
for the voluntary movements leave tthe brain. The pre-central area is called
primary motor cortex, and also "Area 4" in primates.


III. Human and Chimp Cortex Differences

In humans Area 4 is almost twice as large as it is in chimpanzees. The
part of Area 4 that commands the movement of the leg, foot and toes is smaller
in humans than apes. This leaves more room for the part that controls the hand,
fingers and thumb. Even bigger is the lower part of human Area 4, related to
the mouth and brething and vocal cords. The post central cortex is enlarged the
same as Area 4.
In front of the primate Area 4 lie the cortex areas (pre-motor) that tell
Area 4 what to do. In front of the enlarged part of human Area 4 is the Area of
Broca, the motor-speech center which controls the breathing muscles. Above Area
Broca is Wernicke's Area, the speech center, a uniquely human brain center along
with Area of Broca. Wernicke's Area has direct connections to Broca's Area
through arcuate fasciculus, a neural pathway that apes don't have anywhere in
their brain.
The major difference between the human and ape cortex's is the enlargement
of the hand and mouth integration areas. These areas occupy a large part of the
human brain.ý In the motor half of the cerebral cortex, enlarged areas are in
the pre-motor area and Broca's Area. In the sensory half, the enlarged ares are
Wernicke's Area and the visual area as well as the auditory cortex.ý

IV. Explanations

Many anthropologists believe that the differences between human and ape
brains are shown through man's ability to use tools and language. This
traditional view cannot explain why only human ancestors developed these motor
skills and language abilities, that is, why nonhuman primates and other savannah
mammals didn't develop these abilities.
The solution may lie in the aquatic theory of human evolution, the theory
that explains why humans don't have fur, and why we have excess fat, and many
other human features.(4) There are indications that the early hominoids
(ancestors to man and ape) lived in mangrove or gallery forests(5), where they
adapted to a behavior like proboscis monkeys, climbing and hanging in mangrove
trees, wading into water and swimming on the surface. In my opinion human
ancestors, split from chimpazees and other apes and, instead of staying in
forests like chimps, progressed with their water skills, like diving and
collecting seaweed, then adapted to waders in shallow water and finally to
bipedal walkers on land.
The fact that human olfactory bulbs are only 44% of the chimpanzee bulbý,
is not compatible with African savanah life. All savanah animals have a good
olfaction. But an aquatic evolutionary phase would explain why humans have a
poor sense of smell. Water animals typically have a reduced or even non-
existent sense of smell.(4)
The human Area 4 for the legs, feet and toes are reduced, because human
left the trees and lost the grasping hind limbs of apes. Area 4 for the hands
and fingers are larger than apes. The human hand is much more mobile than an
apes, the thumb and index finger in particular, the human fingertips are more
sensetive, we have faster-growing fingernails. All of these enhancements point
towards the enhanced hand mobility and sensitivity of raccoons and sea otters,
which suggests that human ancestors groped for crayfish and shellfish underwater,
also the mobility was needed to remove the shells of the food. Raccoons are
good climbers but seek most of their prey in shallow water. They have human
like forelimbs and fingersý. And their brain cortex shows the same types of
enlargements as humans. Sea-otters, humans, and mongrove monkeys all use tools,
unlike savannah mammals.(5)
Like humans, all diving mammals have excellent airway control, to keep the
water out of their lungs. This voluntary control of breathing is necessary
because they have to inhale strongly before they dive, and under water they have
to hold their breath until they surface. In land mammals, however, exhaling and
inhaling breathing rythms change involuntarily. with lower oxygen and higher
carbondioxide. An aquatic mammal with that mechanism would inhale strongly when
its need for oxygen was the highest, in other words, it would inhale
involuntarily while underwater. That's why the human ancestor tripled the part
of Area 4 for the mouth and airways, and why he evolved the Broca area which
coordinates the muscles of the mouth airways. This refined airway control was a
preadaptation for human speech.(4)


V. Speech and Association Areas
The arcuate fasciculus in humans directly connects the coordination center
of the muscles needed for breathing (Broca) with the cortex behind the sensory
areas for the mouth and throat (where we feel the movements our breathing,
singing, talking etc. make) and the audio areas (where we hear and register the
sounds we hear)(5). This connection of airway sensation with hearing was the
beginning of learning to make voluntary sounds. In the primitive' part of
Wernicke, the first interpretations of sound are made possible through
connections to the visual and paretial areas, so that the sounds were associated
with what we were seeing and feeling when we heard the sound.
Once the connection of Wernicke and Broca was made, we got a device that
could both make sound and interperet it. Using that apparatus we learned to
communicate with the others living in our group. We bettered our communication
abilities by evolving larger areas for the use of our new mechanism.
Apes lack the association ares. Any ape could have evolved a greater
amount of brain tissue and developed the larger association areas, if the ape
had found a need for the extra brain. But, the larger association areas were
useless without the improved sound making/interpereting areas found in humans.
Voluntary and variable sound production seen in aquatic animals like otters,
seals, sea lions, and toothed whales. Large brains are a feature of many
aquatic animals, seals and toothed whales. The relation between aquatic life,
brain size and vocal control is not clear. But even the small-brained sea
mammals have fairly well-developed vocalization skills.

VI. Brain Lateralization

An important difference between a human brain and an ape's brain is the
larger amount of asymmetry in human brains. Like humans being right-handed, is
more pronounced than dexterity of monkeys or apes.(4) Most mammals and birds
show small signs of asymmetry in certain brain functions. The left part of the
brain, in most people, is larger than the right half. (Remember that the left
half of the brain controls the right half of the body and vice versa.) In 65%
of people, the left planum template, where the hearing centers are, is much
larger than the right one. Musical learning that occurs before the age of seven
seems to induce strong enlargement of the left planum temporale. In more than
80% of people the same hemishpere controls the dominant hand (right). Why is
that?
The right hand is usually the hand that does things with an object while
the other hand holds the object steady. The left hand holds the shield, holds
the billiard cue, and holds the paper when writing. This fits with the spatial
and geometricality of the right hemishpere. The right hand is not completely
dominant, there is a small division of tasks between the left and right brain
centers for the hands, especially with jobs that two hands have to be used in.
Some people say that our dexterity came from an ancestor that picked fruit
with one hand while stabalizing himself by holding onto a branch with the other
hand. Although apes are sometimes right or left-handed for certain tasks,
systemetic handedness in the human sense has hardly been demonstrated so far in
nonhuman primates. One explanation for humans having more refined dexterity
than apes is that diving homonids used the right hand to get shellfish from the
bottom of waters while the left grasping something to keep them on the bottom.
Or they used a rock to open the shell while the left held the mussel or oyster
etc. That could be the beginning of human tool use.
Hands are paired organs. Each hand needs its own control center in the
brain. The two centers can be symmetrical -- like apes or, like humans when
each hand has a different function -- more or less asymmetrical. However, an
unpaired organ works better if it has one brain center dominating over the other,
so that fine movements would not be messed up by commands from the other brain
center. A good coordination of the breathing muscles would be essential, the
need for dominant brain centers made dominant brain centers.
Song production in birds is strongly asymmetrical. In adult finches,
section of the left nerve for the syrinx leads to the loss of most of the song,
but the right section has only minor effects of song loss. If the left nerve is
cut before song develops, the right takes over completely.
Human speech centers, too, show a great deal of plasticity. The
localization of Braca's and Wernicke's Area in the left hemishpere is more
constant than human dexterity: not only right-handers, but also most left-
handers, have their speech centers in the left hemisphere of their brain. Is
there any relation between right/left-handedness and the location of the sound-
interpereting/making device? The fact that the control of our dominant hand is
usually situated on the hemisphere of speech centers could mean that the
earliest language use in human ancestors were the naming of objects that were
manipulated or pointed at with the right hand. Or is it simply cooincidence.

VII. Conclusions
The changes in human brain anatomy, compared with the brain anatomy of apes
and monkeys, fits with the aquatic theory of human evolution and have
relationships with aquatic and semiaquatic mammals.
Reduced olfaction is typically seen in aquatic mammals.
Diminished foot control is a feature of nonarboreal (not living in trees)
mammals.
Very refined finger control is a feature of shallow-water feeders.
Perfect control of the airway entrances is essential in diving mammals.
Elaborated vocal ability is seen in aquatic mammals.
A large brain is seen in aquatic mammals such as seals and toothed whales.
Brain asymmetry leads to an aquatic ancestor in human evolution history.

Result: Homo Aquaticus? I think so. And I thik I have proved to myself well
enough to believe in the theory.