Human Evolution

What is it that makes us essentially human? Our name, Homo sapiens, means "wise man." Intelligence is the quality most widely seen as making humans unique. Fossil evidence of intelligence is based upon brain size measured in volume (cubic centimeters). Human brains are three times larger than any comparable primate of a similar weight. Although they grow after birth at a rate that is average for a mammal, they continue to grow for much longer than other animals. Our brains also have different proportions than other primates. Particular areas of the human brain have developed in unique ways, especially the parts of the brain responsible for speech. The other physical traits that we have uniquely acquired include an upright posture, walking on two feet, and an opposable thumb. Finally, human young are cared for over a longer period of time than any other primate.

Many paleontologists argue that evidence of culture, such as making fire and tools, using spoken language, and having self awareness are some of the less tangible but important qualities that differentiated human ancestors from other animals. Other animals besides humans use tools, such as chimpanzees that fashion twigs into devices to poke termites from a termite mound. However, humans make tools with anticipation of using them in the future. In addition, we have become advanced in our tool making capabilities that we can extend our powers of observation beyond our senses. Some species of animals communicate using complex sounds or show evidence of aiding another, such as dolphins and whales. Although other primates do not use symbolic language, where the meaning of words is learned, they are capable of leaning our system of symbols; chimpanzees and gorillas have been taught to use and understand American Sign Language. Humans are unique in having developed written languages.

There is no direct evidence of when or how self-awareness first arose in humans, but some indirect evidence is available. It appears that only humans exhibit awareness that someday they will die. This death awareness leads humans to bury their dead, and intentional burial leaves a trace in the fossil record.