The role of ancient gene duplication in vertebrate evolution is controversial. Two Advanced Early Publications in Nature Genetics explore the nature of human genomic duplications. McLysaght et al. report a systematic analysis of the human genome sequence to find and characterize paralogous chromosomal regions (called paralogons; Nature Genetics, 18 May 2002, DOI:10.1038/ng884). They found many examples of paralogons in the human genome. Comparison with orthologs in Drosophila and nematodes suggested that duplication events occurred around 350-650 million years ago. The authors propose that their results are compatible with at least one round of polyploidy early in chordate evolution. Gu et al. analysed 749 gene families across a number of vertebrate species (Nature Genetics, 18 May 2002, DOI:10.1038/ng902). They propose a model involving two waves of duplication during evolution. The exact nature and importance of large-scale duplication events is likely to remain hotly debated.