Exclusively created by nature.
The most amazing calculating machine ever devised on our planet (and possibly in the universe until we discover otherwise) is not one created by humans but by nature. There are no moving parts such as gears; no mother-board, no central processing unit (CPU), no Random-access Memory (RAM), no hard disk drive or video card, just 100 billion neurons that gather and transmit signals in addition to dendrites and axons that neurons use to transmit those signals. The human brain is made up of approximately 75 percent water and is the fattiest organ in the body, consisting of a minimum of 60 percent fat. It is the main organ of the human nervous system and is connected to the spinal cord. The two make up the central nervous system. The brain consists of the cerebrum, the brainstem, and the cerebellum. It controls most of the activities of the body; processing, integrating and coordinating the information it receives from the sense organs; making decisions and sending instructions to the rest of the body.
The modern human brain began its journey approximately 7 million years ago. Around that time, give or take a million years, a creature arose from the ape population that although displaying mainly ape-like habits such as walking on four feet or knuckle-walking, also had the ability to walk on two legs: the very first bi-pedal member of the ape family from which we, homo-sapiens have arisen. This creature is not our direct ancestor but one of 28 and counting very early hominoids that were to bloom, flourish and become extinct over the following millions of years.
This creature is named Paranthropus Aethiopicus. It had a brain capacity of around 450 cc, about one third that of modern humans, but larger than a chimpanzee, our closest living relative. Evidence is slowly appearing that indicate Aethiopicus may have been the first tool user.
How the human brain grew from 450 cc to its current size has been the subject of much debate, but it is closely linked to a gradual change of diet from nuts, roots and fruit to more meat-based. The earliest stone tools that have been found indicate they were used to scrape the meat off scavenged bones and to smash them to access the high protein marrow inside. Nature determined that a bigger brain made a better brain and evolution forces tended to favor smarter animals.
More human apes were to follow Aethiopicus including Australopithecus Garhi who lived around 2.5 million years ago who began using a more sophisticated variety of stone tools. Brain size appears to have gradually increased in size over the next million or so years when Homo Habilis, thought to be a direct ancestor of Homo Sapiens made its first appearance. This early human had a brain size of 950 cc. The shape of their jaws and the size of their teeth indicate they were not the nut, root, tuber and bark eating creatures their predecessors were. This coarse vegetarian diet required a very complex and energy heavy digestive system.
Habilis has been nick-named Handyman due to its quite sophisticated tool-making abilities and whose diet was becoming much more protein-heavy. A diet of high protein food of any kind including meat scavenged from animal kills, termites, rodents and small animals made larger brains inevitable. As our ancestors consumed more meat, their bodies redirected the energy their complex digestive systems required to building bigger brains. Scientists have accumulated evidence these early humans exchanged brawn for brains. By developing the use of fire and utilizing it for cooking, it made meat and gathered foods more digestible, reducing the need for the complex digestive system. One possible leftover from our plant-eating ancestor may be the human appendix. It is a small pouch attached to the large intestine where it joins the small intestine and does not directly assist digestion.
Jumping ahead in time to early homo sapiens (us) who appeared on the earth's calendar around 200,000 years ago, brain size had increased to about the same size as modern humans, around 1,345 cc, slighter larger in males and slightly smaller in females with the difference in size between the sexes having nothing to do with intelligence levels.
The bigger brains in developing modern humans created a major problem. Females had to give birth far earlier than their ancient forbears as the baby with the bigger brain could not pass through the birth canal after a certain stage. Scientists believe this evolutionary change began when the brain of an ancient predecessor reached an adult size of 850 cc. Anthropologist Robert Martin calls this the "Cerebral Rubicon", a line that once crossed would require a much longer childhood. When comparing newborn chimpanzees and humans, a chimp baby is born with the ability to climb on its mother's back and within a few months become almost self-sufficient. The human baby is helpless for the first year of life. It is then completely reliant upon its parents for several years following. The baby's brain at birth starts around 370 cc and increases, during that first year of life, to about 960 cc after which the growth rate declines.
Studies indicate modern age children under the age of five use 40 to 85 percent of their metabolic rate to maintain their rapidly growing brains. Upon reaching adulthood, that rate drops to 15 to 25 percent.
It is the brain's neurons that make possible our brand of thinking, feeling, seeing, moving and nearly everything else important to us as human beings. The 100 billion neurons that are the machinery of our brain, are clustered inside our skulls in a lump of jelly-like grey matter.
This amazing machine has developed over millions of years. It has taken us from a fearful half-ape, half-human being who existed long enough before the use of fire to avoid extinction, to the moon and back. It has allowed us to reshape the planet we live on in such a way we could be the means of destroying ourselves. Our brains are creative and destructive. They allow us to create beautiful art and weapons of self-destruction. They have provided humans with the ability to live in comfort and to travel globally and, to create machines that could result in our own destruction.
Where goes the human brain in the next 200,000 years if we survive that long? We used to say "the sky is the limit". Now, we look and explore past the sky.