The cultivated tomato, Solanum lycopersicum, originated in the Andes region of South America. It began as a tiny, unassuming berry that bore little resemblance to the large, fleshy globe found in modern grocery stores. Centuries of human intervention, through selective planting and scientific breeding, radically altered the tomato’s appearance, size, and growth habit. This transformation from a small, self-seeding plant to today’s highly optimized fruit demonstrates a profound shift driven by human preference for specific visual and physical traits.
The Original Wild Tomato
The ancestor of the cultivated tomato is the wild species Solanum pimpinellifolium, often called the currant tomato. This ancestral fruit was remarkably small, typically measuring less than a centimeter in diameter, comparable in size to a blueberry. The plant was a sprawling, viney, and indeterminate weed, meaning it would continue to grow and fruit until frost or disease stopped it. The small fruits had a simple internal structure, typically containing only two seed chambers, or locules, contrasting sharply with the multiple locules seen in larger, cultivated varieties. The cherry tomato, S. lycopersicum var. cerasiforme, was a slightly larger intermediate form that bridged the gap to domestication, but its diminutive size made it unsuitable for mass cultivation or long-distance transport.
The Genetic Drivers of Change
The radical increase in tomato size resulted from a few powerful genetic mutations favored by early cultivators. This selection process created a severe genetic bottleneck, carrying forward only a small fraction of the wild species’ genetic diversity. One significant change involved the gene fruit weight 2.2 (fw2.2). The wild version of fw2.2 negatively regulates cell division, limiting the fruit’s final size. Early farmers selected plants where mutations reduced this gene’s activity, allowing for a 10 to 30 percent increase in fruit size by increasing cell numbers. Other genes, such as ovate, were selected for their effect on fruit shape, shifting the form from the ancestral round sphere to more elongated or pear-shaped types.
Early Varieties and the Shift to Red
Following domestication in Mesoamerica, tomatoes exhibited a wide range of colors, shapes, and sizes before modern standardization. Early cultivated varieties, known as heirlooms, were commonly yellow, orange, green, purple, or black, often displaying stripes or splashes of color. The Italian name, pomo d’oro (“golden apple”), suggests that the first varieties adopted in Europe were yellow or golden-orange. These older varieties were frequently irregular in shape, featuring deep ribs, lobes, and grooves, unlike the smooth surface of a typical supermarket tomato. The shift to uniformly red, unblemished fruit occurred later, driven by post-World War II industrial agriculture and the need for fruit that could withstand mechanical harvesting and long-distance shipping. Breeders selected for the uniform ripening gene (the u gene), which causes the fruit to change color evenly from top to bottom. While this created the consistent red tomato consumers expect, it reduced the fruit’s lycopene content and often sacrificed flavor for durability.