Although much biological research depends upon species diagnoses, taxonomic expertise
is collapsing. We are convinced that the sole prospect for a sustainable identification
capability lies in the construction of systems that employ DNA sequences as taxon
'barcodes'. We establish that the mitochondrial gene cytochrome c oxidase I (COI)
can serve as the core of a global bioidentification system for animals. First, we
demonstrate that COI profiles, derived from the low-density sampling of higher taxonomic
categories, ordinarily assign newly analysed taxa to the appropriate phylum or order.
Second, we demonstrate that species-level assignments can be obtained by creating
comprehensive COI profiles. A model COI profile, based upon the analysis of a single
individual from each of 200 closely allied species of lepidopterans, was 100% successful
in correctly identifying subsequent specimens. When fully developed, a COI identification
system will provide a reliable, cost-effective and accessible solution to the current
problem of species identification. Its assembly will also generate important new insights
into the diversification of life and the rules of molecular evolution.