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Evolution

I was researching about the similarity in human and chimpanzee and found out that we are not as similar as originally thought...If so, what is man's closest species relative and why do we still differ so much?

-A high school student from Michigan

February 3, 2011

Chimpanzees (which includes Bonobos) are still our most closely related species. It is just that we aren't as similar as people once thought.

So nothing has changed the fact that humans and chimpanzees shared a common ancestor 7 million or so years ago. What has changed is the DNA differences that scientists have been looking at.

DNA is made up of four different chemicals called A, T, C and G. If you compare humans and chimps, you'll see that two of these letters are different out of every hundred. This is why scientists used to say that human and chimp DNA was around 98% identical.

What has changed is that scientists are now looking at more than these sorts of single letter changes (called SNPs). Now they're looking at bits of DNA that have gone missing (deletions) or extra bits that have been copied (insertions). When you look at these, the similarity drops to 95%. But this is still more similar to any other living thing out there.

Similar But Different

We obviously look different and behave differently than chimps. So how can a few percent of DNA have such an impact?

First of all, remember that we are talking about 6 billion letters of DNA here. The original 2% actually adds up to 12 million differences. Add on top of that another 28 million worth of missing and extra DNA and you start to get some serious differences even if it is only 5%!

Most of these differences don't matter, but a few do. Some will lead to us being less hairy, better speakers, poorer climbers, etc.

You may have noticed that up until this point we've been talking about little tweaks here and there. We haven't talked at all about chimps and people having different genes. And that is because for the most part, they don't. Chimps and humans share most of the same genes.

Apparently a big part of what makes us different are differences in how we use these genes. Numerous studies have shown the same genes behave differently in chimps and humans. This means that a gene might, for example, be less active in humans or active at a different time or different location in the body.

As we start to think a bit deeper about all of this, maybe the small difference between humans and chimps at the DNA level is reflected in actual differences too. Really, how different are humans and chimps?

Chimps and even gorillas can learn language and even make sentences. They use tools and show much of the same behavior we do. They can even understand abstractions like their reflection in a mirror.

Look at body hair. Both humans and chimps have it, but chimps have a lot more. Possibly, humans have very similar hair genes to chimps, but they're just less active resulting in less hair.

Let's look a bit deeper at language too. Even though it is still unclear exactly which of the 40 million differences allow our brains and language to be more complex than that of chimps, we do have clues about where to look.

The difference almost certainly is not new genes. Instead it is things like changes in human vocal chords that allow for the subtle sounds needed in a complex language. We probably had a mutation or two in a vocal cord gene in our recent past.

So chimps are still our closest living relatives. But we've had much closer relatives before. In fact, some of them are still walking amongst us (sort of).

Neanderthals: Not Completely Extinct!

I mentioned before that chimps are our closest relatives. But what I actually should have said was our closest living relatives.

We actually had much closer relatives not so long ago. The most famous are probably the Neanderthals but there were plenty of others too. Some came before us and some shared the Earth with us at the same time. But all the others have gone extinct and we (Homo sapiens) are the only survivors.

Diagram of how humans evolved.

It is still somewhat of a mystery why all other species of humans went extinct. For example, Homo erectus walked the Earth for 2 million years. We probably met them, but they vanished about 70,000 years ago.

Likewise we shared the planet with Neanderthals until they also died out about 30,000 years ago. But recently, scientists have discovered something astonishing. By retrieving DNA from old Neanderthal bones, they discovered that Neanderthals are not completely extinct! They still live on in non-Africans.

To be exact: as we previously talked about here, scientists compared Neanderthal DNA to that of modern humans. Surprisingly they saw that Europeans and Asians still have a few percent of Neanderthal DNA in their chromosomes. This suggests that hundreds of thousands of years ago, we did not just "meet" Neanderthals: we mated with them! And although Neanderthals went extinct, parts of their DNA lives on in present day Europeans and Asians.

Dr. Hinco Gierman, Stanford University


Still our closest living relative.


Our family tree.
The further to the right the branching, the more closely related are the species.