What makes us human?

How to turn an ape into a human
Why are we so different from other animals? How did we get such a big brain? Why can we talk? Until recently, these questions were nearly impossible to answer. But now, scientists are starting to figure them out. How are they doing it? By comparing our DNA to the DNA of other species like apes, dogs or fish. All species have their own sequence of DNA; that is what makes them separate species. The idea is that if we can figure out what the differences are, then we'll be able to figure out what sets us apart. The DNA sequence most useful in answering the question of what makes us human is the chimpanzee's. About 6 to 8 million years ago, two groups of apes became separated. They stayed separated long enough to evolve into two different species, humans and chimpanzees. This evolution was a gradual process resulting from small changes in DNA over time. In other words, all of the changes that make us biologically different from the chimp are at the DNA level. That's easy then, just figure out the differences and you're done, right? Well, no, it's actually much harder than that. First, about 1.5 % of our DNA is different from that of the chimpanzee. This might not sound like much but since our DNA is made up of 3 billion base pairs that means there are 45 million differences between our DNA sequence and that of the chimps. The second problem is that not all of these changes are responsible for making us humans. There are lots of changes that have nothing to do with turning an ape into a human. So as you can probably guess, finding out which of those 45 million differences were needed to make us stand upright or get bigger brains is actually pretty daunting. In two different types of studies, scientists have recently found DNA differences that may have made our distant ape ancestors more human. The two studies start by figuring out DNA changes or mutations that have happened within the last 6 million years. The scientists argue that these mutations somehow helped our ancestors and also made them more human like. The first mutation is in the MYH16 gene and may have allowed our brains to grow bigger. The second mutation is in the FOXP2 gene and may have helped us acquire language.

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Less muscles, more brain
One of the things that separate us from chimps is our big brain. How did we develop such big brains while the chimp's stayed relatively smaller? To answer this question we have to find the DNA mutations that gave us bigger brains. Some researchers now think that they may have found one of these mutations, in the MYH16 gene. Humans all have this mutation but other primates including the chimp don't. As explained above, this is only one of the many differences predicted between human and chimp. What tells us that this particular change was important for human evolution? The mutation in the MYH16 gene probably gave humans weaker jaw muscles. So how do weaker jaw muscles lead to a bigger brain? Studies have shown that when muscles change, the bones attached to them can change too. It is possible that smaller jaw muscles allowed for the reshaping of the skull and at some point for the enlargement of the brain Another piece of supporting evidence is that the mutation appears to be about 2.4 million years old. This is about 400,000 years before humans developed smaller jaw muscles and our brains started to enlarge. The mutation may have been necessary for the morphological change. The idea that a mutation in a gene that shapes muscles may have contributed to the evolution of the human skull is very interesting. Researchers now have to do more experiments to strengthen their theory.

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Did FOXP2 mutations make us better speakers?
Another difference between chimps and us is that we can talk but they cannot. We do not know the exact time when our ancestors learned to talk. All we know for certain is that humans could speak 50,000 years ago when they were making art and burying their dead. What DNA mutations have given us the ability to talk? Researchers found that the FOXP2 gene may be one of the genes that helped us improve our speech over the last 200,000 years. It was already known that people with a specific mutation in the FOXP2 gene have a hard time speaking. This suggested that FOXP2 is important for speech. The researchers also found two important changes in the gene that have happened in humans after we diverged from the chimpanzee. The mutations are between 100,000 and 200,000 years old. So they happened around the time humans developed language. Maybe these changes made our ancestors better speakers.