Adaptation of plants to soils containing toxic metals--a test for conceit

Darwin, and many biologists afterwards, have seen few, if any, limits to the processes of adaptation by evolutionary change. Perhaps we have been conceited. A study of heavy-metal tolerance, and other conditions to which evolutionary adaptation has occurred, should overwhelm us with evidence for limits to the evolutionary process and limits to the adaptation it achieves. These limits clearly arise from restrictions in the supply of genetic variability. Nearly all species are in a condition of genostasis, in which there is a lack of appropriate variability for further evolutionary change. It is the molecular biologist who, by understanding the architecture of genes, will ultimately be able to explain what failures and limitations in genetic architecture at the molecular level cause the limits to adaptation itself.