As any undergraduate biology student can tell you, to understand the variability in a biological system and come to robust generalized conclusions, it is crucial to obtain independent replicates for comparison. Although this is not so difficult when you are doing experiments on Drosophila or cultured populations of bacteria, it is less straightforward when studying whole genomes. However, even in genomics, and despite the effort required, the benefits of comparison are clear, as illustrated in the Review by Carlos López-Otín and colleagues on page 544, which provides a comprehensive comparative analysis of the mouse and human degradomes.

The Review on page 497 by Michael Rudnicki and colleagues illustrates the power of comparing tissue-specification processes in the embryo and adult. It discusses the relevance of transcriptional networks in embryonic myogenesis to the development and differentiation of adult muscle cells.

Christos Ouzounis and colleagues make comparisons of a different sort in their Review on page 508, which discusses different protein classification schemes. The plethora of structural and functional schemes has hampered the free flow of information, and this article makes the case for a single protein taxonomic system.

Of course, a big part of developing new technology is also about comparison: assessing how the newcomers measure up against established techniques. Two recent papers discussed in the Highlights section, which report improved methods of using RNAi to make tissue-specific mouse knockdowns (page 494) and of haplotyping SNPs (page 492), illustrate this point.

So, in biology at least, the old dictum that “comparisons are odious” couldn't be farther from the truth.