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How much truth is there to this childish game? What really separates this human child from the object of its mimicry? See more pictures of mammals.

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What separates humans from chimps and other apes?

Human beings see themselves in everything. We establish emotional connections to animals with facial features resembling our own infants. It's nearly impossible for us to mark two dots on a sheet of paper without seeing a pair of eyes staring back at us. We've even gazed into the night sky and marked the shape of our own ephemeral bodies against the timeless spill of stars.

It's not surprising then that we stare at gorillas and chimpanzees and see aspects of ourselves: the bestial, the innocent, the savage and the adorable. And unlike kittens or distant constellations, we actually have a great deal in common with apes. We're all tailless primates, belonging to either the Hylobatidae family (in the case of gibbons) or the Hominidae family, which encompasses chimpanzees, bonobos, orangutans, gorillas and human beings. Among the apes, humans have the most in common with chimps. In fact, go back 5 or 6 million years and you'd find a common ancestor that both humans and chimps share. We also share between 94 and 99 percent of the same genes, depending on the study.

That meager percentage encompasses the gulf of difference between the animal wilds and the human world of empires, science, architecture and spirituality. We're both shackled to so much of the same genetic programming, yet humans take the same basic yearnings and exaggerate them to hideous proportions. Tribal allegiances escalate into wars of extermination. Mating games become industry and art. Our hunger shapes and scars the planet.

Approximately 10 million years ago, the great apes splintered off from their evolutionary kin. Between 200,000 and 250,000 years ago, Homo sapiens emerged on the scene, and the species began its slow ascension toward global domination. What truly set this particular strain of life apart?

Why are we the ones standing on the free side of the cage?

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A gorilla warms himself in the London Zoo's Gorilla Kingdom. See more pictures of primates.

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A Planet Where Men Evolved from Apes?

Physically, apes are virtually superheroes compared to us. For example, chimpanzees are roughly four times more powerful than the average human [source: ScienceDaily]. While humans lack the sheer power of the mighty chimp, our nervous systems exert much more control over our muscles, enabling us to execute far more subtle movements.

Humans possess superior motor control, less body hair and a far more advanced brain. Neuroscientists have identified substantially more intricate nerve connectivity in the human brain, as well as some things called spindle neurons. Also known as Von Economo neurons (VENs), these cells appear most frequently in areas of the brain associated with social emotions.

Under "social emotions," you'll find a whole Pandora's box of human characteristics, including empathy, guilt and embarrassment. The consensus is that although humans have evolved socially from our last common ancestor, chimps have remained largely the same. Our two species still share such bloody traits as male kin bonding and lethal territorial aggression. Human males and females, however, share a deeper conjugal bond, creating family-based society. Chimps, on the other hand, have separate male and female hierarchies.

Such differences depend on often slight genetic details. While human and chimps share similar gene sequences, copy number variations can differ greatly. These include code repetitions, deletions and backward sequences. If we were to compare it to something as simplistic as human names, on one hand you have the name "Jim Morrison," which is different from "Jim Jim Morrison," Morrison Jim" or the Doors front man's anagram pseudonym, "Mr. Mojo Risin.'" Among humans, copy number variation can distinguish one identical twin from another and have also been associated with various diseases, such as AIDS [source: Fox]. In other words, it's not just what the genes are, but how they're expressed.

Could ancient dietary changes have set the course for human and chimp evolution?

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Primate Evolution: Climbing the Tree of Knowledge

Scientists believe that an explosion of just such genetic changes caused the lineage of the great apes to branch off from the lesser, tailed primates 10 million years ago. Then, 2 million years ago, a similar genetic burst splintered humans off from the rest of the apes. In comparing genetic differences between humans and other apes, scientists at Cornell University reached a theory that the split between humans and chimps might have very well come down to issues of scent and taste [source: Cornell News].

The Cornell team found hundreds of gene sequence changes in areas related to, among other things, smell and digestion. Obviously, humans are the most evolved primate species on the planet, with chimps coming in second. The hierarchy also exists when you look at meat consumption among primates. Chimps are only surpassed in meat consumption by humans. Researchers suggest that a dietary change brought on by sudden climate change may be the key catalyst behind the explosions in evolution that separated humans and chimps from our most recent common ancestor. The genes involved also affect long-bone growth, hairiness and hearing -- the last of which is closely connected to the development of speech.

Increased meat eating also may have lowered the physical playing field between males and females. Primatologists believe that a new mating system emerged 1.9 million years ago among humans, replacing the dual male-female hierarchy with more of a team effort. As males shared more meat with their females, females grew in size and were able to produce bigger children with larger brains [source: Wade].

If these findings are correct, it means that man's appetite set him on the evolutionary path to global dominance -- an insatiable hunger that continues to shape the future for all life on this planet.

Explore the links on the next page to learn even more about the relationship between humans and other apes.

Lots More Information

Related HowStuffWorks ArticlesMore Great LinksSources
  • "DNA analysis for chimpanzees and humans reveals striking differences in genes for smell, metabolism and hearing." Cornell News. Dec. 18, 2003. (April 24, 2009)http://www.news.cornell.edu/releases/Dec03/chimp.life.hrs.html
  • Fox, Maggie. "Gene explosion set humans, great apes apart." Reuters. Feb. 11, 2009. (April 24, 2009)http://www.reuters.com/article/idUSTRE51A8II20090212
  • "Human-chimp Difference May Be Bigger." ScienceDaily. Dec. 20, 2006. (April 24, 2009)http://www.sciencedaily.com/releases/2006/12/061219201931.htm
  • "'Humans not just "big-brained apes,' researcher says." PNAS and World Science. Aug. 22, 2007. (April 27, 2009)http://www.world-science.net/othernews/070821_humans.htm
  • Kreger, C. David. "Homo sapiens." Archeology.info. 2008. (April 24, 2009)http://www.archaeologyinfo.com/homosapiens.htm
  • Lovgren, Stefan. "Chimps, Humans 96 Percent the Same, Gene Study Finds." National Geographic News. Aug. 31, 2005. (April 24, 2009)http://news.nationalgeographic.com/news/2005/08/0831_050831_chimp_genes.html
  • "The Secret to Chimp Strength." ScienceDaily. April 8, 2009. (April 24, 2009)http://www.sciencedaily.com/releases/2009/03/090330200829.htm
  • Wade, Nicholas. "A Course in Evolution, Taught by Chimps." New York Times. Nov. 25, 2003. (April 27, 2009)http://www.nytimes.com/2003/11/25/science/a-course-in-evolution-taught-by-chimps.html?sec=&spon=&pagewanted=1