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
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...ain. 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.
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.