Watermelons do grow in the wild, but the fruit found naturally is significantly different from the large, sweet variety typically purchased in a store. The cultivated plant is the result of thousands of years of human selection and breeding. Botanically, the watermelon is a species of flowering plant, Citrullus lanatus, belonging to the Cucurbitaceae family, which also includes squash and cucumbers. The wild form is a much less palatable fruit.
The Ancestry of Watermelons
The origins of the watermelon lie in the arid regions of Africa, specifically Northeast Africa, around the Nile Valley and Sudan. Genetic studies and archaeological evidence point to this area as the center of diversity for the species. Seeds of wild watermelons dating back approximately 5,000 years have been discovered in prehistoric sites in Libya.
The wild fruit’s characteristics were markedly different from the modern dessert type. These early watermelons were typically small, with pale, hard-textured, and often bland or bitter flesh. Early cultivation, suggested by tomb paintings in Egypt from over 4,000 years ago, focused on the fruit primarily as a source of water and moisture. One modern relative, the Kordofan melon found in Sudan, is considered the closest living precursor to the domesticated watermelon, having a non-bitter, whitish pulp.
The Process of Domestication
The transformation from the wild, unpalatable fruit to the modern sweet variety was a long process driven by selective breeding over millennia. Early agriculturalists chose seeds from plants that produced fruit with less of the bitter compounds. The genetic component responsible for the bitter taste, called cucurbitacins, was gradually selected against.
This process involved a stepwise genetic shift, where bitterness genes were negatively selected and genes promoting desirable traits were positively selected. Humans selected for higher sugar content, increasing sweetness. The deep red color resulted from selecting for greater accumulation of the pigment lycopene. The sweet dessert watermelon is thought to have emerged in the Mediterranean lands around 2,000 years ago.
Differences Between Wild and Cultivated Varieties
The physical differences between the original wild watermelon and the cultivated variety are pronounced. Wild fruits are generally much smaller, rarely exceeding 20 centimeters in diameter, while cultivated varieties can grow to be three times that size. The wild fruit’s flesh is typically pale white or yellow, dense, and firm, contrasting sharply with the tender, juicy, deep red flesh of the modern watermelon.
The most significant distinction is taste, dictated by specific chemical compositions. Wild watermelons contain higher levels of cucurbitacins, making them unpalatable or mildly toxic. Cultivated watermelons have had the genes for these bitter compounds largely bred out, resulting in a high concentration of sugars and lycopene.