Compare the DNA of two people and you see about three million base sequence differences and compare the DNA of a human and chimp and you see about thirty million. This is out of about three billion bases total. So, at the DNA level, people are about 99.9% identical to each other and about 99% identical to a chimp. This just counts single base differences, and not copy number variations and such, but in general it is clear that we are remarkably similar at the DNA level to chimps.
So why are we so incredibly different from chimps?
One view is that we really are not that different. Oh sure, we have Apple computers, Rocket Scientists and Astrophysics. But maybe if you could just tweak a chimp’s brain a tiny bit, and give him language, and books, and a few thousand years, then maybe chimps could have that stuff too.
It is interesting to note that it was recently shown that even bird-brained pigeons have a surprising ability to do some rather sophisticated math reasoning.
We like to think that humans have a monopoly on thinking and reasoning, but we don’t.
But our brains are three times bigger than a Chimps!!
But are big brains all that they are cracked up to be? A sperm whale brain weights 7800 grams, an elephant brain weighs 7500 grams and a person’s weighs 1500 grams. Are whales and elephants really that much smarter than us?
And are those people with bigger brains smarter than those with smaller ones? Big people tend to have big brains. Are football players and basketball players smarter than the rest of us? Men tend to be bigger in general, and to have bigger brains than women. But are they smarter?????
But maybe it is brain size as a proportion of body size. Our brains are about 2% of body weight. A dolphin brain is about 1%, and whale brains come in at around 0.1%. So this might start to make sense. But what about the mouse! It comes in at 3%!! http://www.highnorth.no/library/myths/br-si-bo.htm
So what makes us so special? Maybe God did it. But most scientists would agree that saying God did it is a pretty lame explanation for anything. That’s one reason why most scientists are either atheist or agnostic. (See http://blog.beliefnet.com/roddreher/2010/04/science-vs-religion-what-do-scientists-say.html).
Or maybe it is a special version of the Foxp2 gene that gave us improved brain wiring and speech. People with mutations in this gene have verbal dyspraxia, a severe speech and language disorder. Indeed, some have called this the “language gene”. Chimps have an altered version of this gene, and some suggest that this single difference accounts for a big part of the chimp-human disparity.
Or maybe it was a change in head musculature that allowed our craniums to expand more and accommodate larger brains. It has been shown that humans carry an abnormal version of a muscle myosin gene named Myh16. Stedman has suggested that his resulted in weaker and smaller jaw muscles, which in turn allowed the cranium to expand more and accommodate a bigger brain (http://www.ncbi.nlm.nih.gov/pubmed/15042088).
Or maybe it is related to genes that seem to directly control brain size. People with altered versions of these genes suffer microcephaly, or small heads and brains. One view is that people in general have macrocephaly, or big brains, compared to other species, because of special Homo sapiens versions of these genes. http://www.walshlab.org/
Or maybe we aren’t all that incredibly special at all???? Maybe, again, it is just language and culture that separates us from chimps.