GoKawiilAlex Wakeman explains how centuries of selective breeding turned a single wild weed into everything from broccoli to Brussels sprouts.
Every crop we consume came from a wild ancestor. Through breeding, people selected for bigger grains, juicier fruit, more branches, or shorter stems – gradually turning wild plants into improved yet recognizable versions of their originals. The rare exception is Brassica oleracea, wild cabbage: the origin of cabbage, bok choy, collard greens, broccoli, Brussels sprouts, cauliflower, and much else.
Wild cabbage is unassuming: some untidy leaves and a few thick, coarse stems on the browner side of purple that poke out from the soil. Nothing about it looks appetizing.
Wild cabbage (Brassica oleracea) growing in Northumberland. Source: Wikimedia
Nevertheless, many cultures have recognized something special in this plant. By selecting plants with denser layers of leaves, ancient people created modern cabbage and kale. Others bred for the inflorescence, a dense bundle of small flowers that forms the head of cauliflower and broccoli. By favoring large, edible buds, thirteenth-century farmers living around modern day Belgium created Brussels sprouts. Under different selection pressures, Brassica oleracea has become German kohlrabi, or Chinese gai lan, or East African collard greens.
This level of morphological diversity is unusual. Modern tomatoes, for example, vary in size, shape, and color, but are all recognizably tomatoes. Since the 1920s, scientists have worked to understand how Brassica oleracea was domesticated and to deepen our knowledge of evolution and artificial selection.
By combining modern genetics, genomics, and molecular biology with linguistic, historical, and sociological sources, researchers are now beginning to develop conclusive answers.
Cabbage architecture
Domesticating a plant means prioritizing certain structures over others. Wheat shoots are completely inedible, so farmers have bred plants to focus on their grain. Modern wheat typically grows to around waist height; a few hundred years ago it was closer to head height. These shorter, modern wheat ears also produce more and larger grains than ancient species.
Whereas other plants have a single most useful element, such as the grains of wheat or the fruit of tomatoes, wild cabbage has many. Although people didn’t know about it until the twentieth century, Brassicas are high in fiber and micronutrients like calcium, iron, and vitamin A.
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