The differences between human and chimpanzee DNA may uncover reasons why humans can walk upright, use language and read. Scientists have created a complex tool, the gene expression chip, which enables them to study genetic activity in the brains of humans and chimpanzees. Although anatomists have said that human and chimpanzee brains differ only in size, recent discoveries show that gene networks in the human brain are not found in the brain of a chimpanzee.
The main difference between the chimpanzee and human brain is volume. While an average chimpanzee's brain weighs about 14.4 oz., or less than 1 lbs., a human's brain weight varies from 35 to 63 oz. Humans also have a neocortex which is three times the size expected for a primate with the same body size. Part of the cerebral cortex, the neocortex forms the top layer of the brain's hemispheres, and is responsible for conscious thought, sensory perception, spatial reasoning, language and producing motor commands, according to the Science Daily.
Each hemisphere of the brain consists of four lobes, or frontal, temporal, parietal and occipital. In comparison to the human brain, the chimpanzee brain has much smaller temporal and parietal lobes. The parietal lobe controls sensations, such as pressure and touch, and enables the judgment of size, shape, texture and weight. The temporal lobe is involved in short-term memory and the sorting of information. The human frontal lobe, which is responsible for problem-solving, organizing, planning and other higher cognitive functions, is considerably more coiled than a chimpanzee's frontal lobe, according to Roger Lewin's "Human Evolution: An Illustrated Introduction."
The position of the primary visual striate cortex, which is dedicated to vision, is a region in the brain marked by a dip in the brain's surface known as the lunate sulcus, according to the BBC News. This small groove is found in the boundary between the temporal and occipital lobes. In contrast to the human brain, the chimpanzee's lunate sulcus lies further back in the brain.
In 2006, scientists at University of California, Los Angeles discovered networks of genes located in the cerebral cortex, or the highly evolved area of the brain, which differ considerably between humans and chimpanzees. These genes serve a central function in a human's cerebral cortex, and are associated with metabolism, brain cell activity and the ability to learn. These same gene networks are not found in the chimpanzee. "If you view the brain as the body's engine, our findings suggest that the human brain fires like a 12-cylinder engine, while the chimp brain works more like a 6-cylinder engine," says Dr. Daniel Geschwind at the David Geffen School of Medicine.
- Science Daily; Unraveling Where Chimp and Human Brains Diverge; November 17, 2006
- University of California, Davis; Brain Gene Shows Dramatic Difference From Chimp to Human; August 16, 2006
- "Human Evolution: An Illustrated Introduction"; Roger Lewin; 2005
- "On Becoming Human"; Nancy Makepeace Tanner; 1981
- "Chimpanzees"; Rebecca Stefoff; 2003
- BBC News; Human Brain Began Evolving Early; Paul Rincon; February 17, 2004
- Photo Credit Jupiterimages/Photos.com/Getty Images
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