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How did teeth evolve?

Updated Thursday, 24th February 2011

My dear, what big teeth you have... but how did you (or, indeed, fish) come to have them?

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Chris Smith: Tell us where teeth come from?

Kat Arney: It’s an important question, where do teeth come from? Now not just in terms of popping through the gums of a dribbling baby but in an evolutionary context. And now research published in the journal PloS Biology shows that a common genetic control system is in charge of the development of all known teeth, from the first ever teeth in fish living half a billion years ago, to our own pearly whites.

Fossilised teeth on a jawbone

Chris Smith: It’s a fascinating finding, how did they discover that?

Kat Arney: This is research by Gareth Fraser and his colleagues from the US. And they studied tooth formation in a group of fish that undergo rapid evolution. These are fish known as cichlids that are found in Lake Malawi in Africa.

Now these fish have two sets of teeth, they have one set in their jaws in their mouths and they have another set back in their throat. Now these two sets of teeth are very different in evolutionary and developmental terms; teeth set back in the throat are a much older invention than teeth in your mouth. But the researchers were surprised to find that there was a link between the number of teeth in the mouth of these fish and in their throats, suggesting that there was some kind of genetic link between the two.

Chris Smith: But that could just be a coincidence couldn’t it, how do you prove that it’s down to the same genes?

Kat Arney: Well the researchers used a technique called in-situ hybridisation, which allows scientists to precisely reveal the genetic patterns of activity of specific genes. So using this they found a common set of genes controls the teeth in the cichlids’ mouths and also in their throats. These genes are hox genes which are involved in patterning many of the body’s structures. For example, some of our own hox genes give us the regular pattern of vertebrae in our spines and give us five fingers and toes. Now the scientists found that a precise pattern of hox gene activity, along with other related genes controlled by the hox genes, was needed for developing both teeth in the throat and teeth in the mouth. So it’s likely that the earliest fishes also used hox genes to generate teeth in their throats, and later on in evolution this same genetic pathway got co-opted and hijacked with a few tweaks to create teeth in the mouth.

So the researchers basically think that every tooth made throughout evolution probably uses this core set of genes. And not only that, they think that probably similar pathways are at work in the kind of pattern structures we see in other animals like hair and feathers too.

Extracted from an episode of Breaking Science originally broadcast February 2009. Listen to the full episode online.


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