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A MOLECULE that “blocks” evolution has been discovered in plants. Called heat-shock protein 90 (Hsp90), it eliminates kinks and abnormalities from the regulatory proteins that dictate the growth, development and shape of plants. Christine Queitsch and her colleagues from the University of Chicago found that switching off production of Hsp90 in Arabidopsis thaliana weeds unleashed a burst of natural variation that had been lurking in the plants, including variations in leaf shape and colour (Nature, DOI 10.1038/nature749). The changes were most marked when Queitsch exposed the plants to mild stress, such as raising the temperature by 5 °C. “There is hidden genetic variation and we can uncover it by blocking Hsp90,” she…