IntroductionWhen the human brain is compared with the brains of apes there are severalobvious differences; the centers for the sense of smell and foot control arelarger 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 willdescribe the most defined differences of brain size and centers between humansand their closest relatives, chimpanzees, to compare them with other mammals andto draw conclusions about the evolution history of humans. II.
Brain EvolutionHumans and chimpanzees are biochemically (DNA) and therefore probablyphylogenetically (evolution relationships), more alike than chimps and gorillas.But the brains of chimps and humans differ in size and anatomy more thangorillas and chimps. The brains of chimps and gorillas probably didn’t gothrough many evolutionary innovations, because they generally resemble other apeand monkey brains. This implies that the human brain changed a lot after thehuman/chimp evolution. With the exception of the olferactory bulb (scent), allbrain structures are larger in humans than in apes. The neocortex (part of thecerebral cortex), for instance is over three times larger than in chimps, eventhough chimps and humans are pretty close to equal in body weight.Each side of the brain is diveded by the central sulces into independanthalves.
Just before the central sulcus lies the post-central cortex, where theopposite body half (right side for left brain, left side for right brain). Justin front of the central sulcus lies the pre-central cortex where the informationfor the voluntary movements leave tthe brain. The pre-central area is calledprimary motor cortex, and also “Area 4” in primates. III. Human and Chimp Cortex DifferencesIn humans Area 4 is almost twice as large as it is in chimpanzees.
Thepart of Area 4 that commands the movement of the leg, foot and toes is smallerin 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 tothe mouth and brething and vocal cords. The post central cortex is enlarged thesame as Area 4.In front of the primate Area 4 lie the cortex areas (pre-motor) that tellArea 4 what to do.
In front of the enlarged part of human Area 4 is the Area ofBroca, the motor-speech center which controls the breathing muscles. Above AreaBroca is Wernicke’s Area, the speech center, a uniquely human brain center alongwith Area of Broca. Wernicke’s Area has direct connections to Broca’s Areathrough arcuate fasciculus, a neural pathway that apes don’t have anywhere intheir brain.
The major difference between the human and ape cortex’s is the enlargementof the hand and mouth integration areas. These areas occupy a large part of thehuman brain. In the motor half of the cerebral cortex, enlarged areas are inthe pre-motor area and Broca’s Area. In the sensory half, the enlarged ares areWernicke’s Area and the visual area as well as the auditory cortex. IV. ExplanationsMany anthropologists believe that the differences between human and apebrains are shown through man’s ability to use tools and language.
Thistraditional view cannot explain why only human ancestors developed these motorskills and language abilities, that is, why nonhuman primates and other savannahmammals didn’t develop these abilities.The solution may lie in the aquatic theory of human evolution, the theorythat explains why humans don’t have fur, and why we have excess fat, and manyother human features.(4) There are indications that the early hominoids(ancestors to man and ape) lived in mangrove or gallery forests(5), where theyadapted to a behavior like proboscis monkeys, climbing and hanging in mangrovetrees, wading into water and swimming on the surface. In my opinion humanancestors, split from chimpazees and other apes and, instead of staying inforests like chimps, progressed with their water skills, like diving andcollecting seaweed, then adapted to waders in shallow water and finally tobipedal walkers on land.The fact that human olfactory bulbs are only 44% of the chimpanzee bulb,is not compatible with African savanah life. All savanah animals have a goodolfaction. But an aquatic evolutionary phase would explain why humans have apoor 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