Statistical analyses of the fossil record seek to discover the mechanisms controlling biotic diversity throughout the Earth's history. Sole et al.1 reported that many extinction time series are statistically self-similar, with 1/f power spectra, suggesting that extinctions are driven by self-organized criticality or by other scale-free internal dynamics of the biosphere. Here we show that the apparent self-similarity and 1/f scaling reported by Sole et al. are artefacts of their interpolation methods. Extinction records that are not interpolated show no evidence of fractal scaling.