Key Traits and Mechanisms of Crop Evolution

Key Insight

Human selection for visible traits significantly altered wild plants. Beyond size and taste, early farmers favored increased fleshiness (squashes, pumpkins, seedless bananas), oiliness (olives cultivated since 4000 B.C., sesame), and longer fibers (cotton, flax for linen by 7000 B.C.). This selection sometimes reversed a wild plant's original evolutionary function, as with seedless bananas and modern seedless oranges or grapes, where the fruit no longer serves its natural role of seed dispersal.

Crucially, unconscious selection also acted on invisible traits. Early farmers inadvertently selected for mutations affecting seed dispersal, such as non-exploding pods in peas, lentils, and flax, or non-shattering stalks in wheat and barley. These mutations, lethal in the wild because seeds couldn't disperse, became advantageous for human harvesting. The selection for non-shattering wheat and barley stalks over 10000 years ago marked a pivotal 'improvement' in plants and the beginning of agriculture in the Fertile Crescent.

Further invisible changes involved the selection against germination inhibitors, favoring seeds that sprouted quickly and uniformly, rather than delaying germination over several years as many wild plants do to 'hedge bets' against unpredictable climates. Mutations in reproductive biology were also preserved, leading to self-pollinating varieties (e.g., plums, peaches, apples) or parthenocarpic (seedless) fruits (bananas, grapes, oranges), which ensured desirable traits bred true. This led to a wide array of crops from single wild species, exemplified by beets being selected for leaves, roots, and eventually sugar, and cabbage diversifying into varieties grown for leaves, stems, buds, or flower shoots.