I take issue with the contention that Erasmus Darwin, the grandfather of Charles, tackled evolution only in poetic terms, as implied by Dan Graur and colleagues in their insightful Book Review ('In retrospect: Lamarck's treatise at 200' Nature 460, 688–689; 2009).Erasmus Darwin's most important contributions to evolutionary thought will be found in the very unpoetic prose of the first volume of his major medical and zoological treatise, Zoonomia, published in 1794.