The residues ("tailings") of mines often contain such high concentrations of toxic metals (e.g., copper, lead) that most plants are unable to grow on them. However, some hardy species (e.g., certain grasses) are able to spread from the surrounding uncontaminated soil into such areas. These plants evolve resistance to the toxic metals, while their ability to grow on uncontaminated soil decreases. Because grasses are wind pollinated, breeding between the resistant and nonresistant populations continues, but offspring of crosses between the two populations are intermediate and have low fitness. This is an example of

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This scenario exemplifies disruptive selection, where extreme values for a trait are favored over intermediate values, leading to two distinct populations: one resistant to toxic metals and one that thrives in uncontaminated soil. The intermediate offspring with low fitness indicate that the two extremes are being selected for, which is characteristic of disruptive selection.

The Residues ("Tailings") of Mines Often Contain Such High Concentrations