Homo Aquaticus?

Topics: Brain, Human brain, Cerebrum Pages: 6 (2044 words) Published: October 8, 1999
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...
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