Broccoli, kale, cauliflower, and Brussels sprouts are all the same species of plant.

The wild mustard plant, Brassica oleracea, is native to the coastal regions of southern and western Europe. Over two millennia, human intervention transformed this single species into a diverse array of common vegetables through artificial selection. This process began as early as 500 BCE when farmers in the Mediterranean region began selecting for plants with larger leaves, eventually resulting in the development of kale and collard greens.During the Roman Empire, further cultivation focused on the plant's flowering heads. By selecting individuals with large, immature flower clusters, farmers developed primitive versions of broccoli and cauliflower. It wasn't until the 1700s that the modern version of cauliflower became widely recognized in Europe, while broccoli gained significant popularity in the United States much later, during the 1920s.Brussels sprouts are a more recent addition to the family, first documented in the 13th century in what is now Belgium. They were created by selecting for plants with enlarged lateral leaf buds along the stem. Cabbage was developed by selecting for a large terminal bud that stays tightly closed. Despite these drastic physical differences, all these vegetables share the same DNA and can still cross-pollinate with one another.Botanists classify these distinct groups as cultivars rather than separate species. This means that while they look and taste different, they are genetically the same organism. This evolutionary journey highlights how humans have shaped the modern diet through thousands of years of agricultural experimentation.