Did ancient Egyptian children compete to see who could spit seeds the furthest as they ate watermelons? It seems likely, because thanks to some DNA detective work we now know for sure that the ancient Egyptians ate domesticated watermelons with sweet, red flesh.
The wild watermelons found in parts of Africa are nothing like the domesticated varieties. They are small, round and have white flesh with a very bitter taste due to compounds called cucurbitacins. There's long been debate about when and where they were domesticated, with some suggesting it took place in south Africa or west Africa.
However, pictures on the walls of at least three ancient Egyptian tombs depict what look like watermelons – including one that looks strikingly like modern varieties (pictured below). And in the 19th century, watermelon leaves were found placed on a mummy in a tomb dating back around 3500 years.
When botanist Susanne Renner at the University of Munich, Germany, learned about these leaves, she realised their DNA might reveal what the ancient melons were like. She also discovered that some of the leaves had been sent to the famed botanist Joseph Hooker, then head of Kew Gardens in London. "It was my love of the old literature," she says.
Mark Nesbitt at Kew gave Renner's team a tiny sample of one leaf. He had trouble opening the display case containing the leaves, she says, as it had not been opened since the leaves were first placed in it in 1876.
The ancient DNA was then sequenced by Renner's colleague Guillaume Chomicki, now at the University of Oxford. The team were only able to get a partial genome sequence, but it includes two crucial genes that reveal what these melons were like. "We were so lucky," says Renner.
One of these genes controls the production of the bitter cucurbitacins. In the 3500-year-old melon, there was a mutation that disabled this gene, meaning it had sweet flesh just like modern varieties.
The other gene codes for an enzyme that converts the red pigment lycopene – the same pigment that makes tomatoes red – into another substance. This gene was also disabled by a mutation, meaning lycopene accumulates and the fruit would have red flesh.
What the team can't tell from the partial sequence is how large the melons were and whether they had an elongated shape or round shape. But one of the ancient Egyptian pictures shows what appears to be an elongated melon, so it seems farmers had bred watermelons with most if not all of the key features at least 3500 years ago.
The DNA also reveals that the ancient melon was closely related to a sweet watermelon with white flesh still grown in the Darfur region of Sudan. That suggests the watermelon was first grown by farmers in this region and the use of the plant then spread northwards along the Nile, with further improvements like red flesh occurring along the way.
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