Nature 543, 367–372 (2017); doi:10.1038/nature21359

The legend to Fig. 1 of this Perspective cites ref. 24 twice but both instances should instead refer to ref. 70 (which is listed in the Supplementary Information of the Perspective and below1). Elsewhere in the Perspective ref. 24 is correctly cited. The original Perspective has not been corrected.