Much excitement has surrounded the finding of large amounts of structural variation in the human genome. But what contribution does this make to phenotypic variation? A recent study provides evidence that human copy number variants (CNVs) have had a role in the adaptation of humans to their surroundings.

Chris Ponting and colleagues looked at CNVs that were identified in previous studies and used a bioinformatics approach to compare features of CNVs with those of the genome as a whole. Among their findings, the authors showed that CNVs are enriched in genes, and that different gene types are present unevenly within them. Genes that are involved in Mendelian diseases are underrepresented, which could be explained if the extra gene copies provided by CNVs compensate for mutations that might otherwise lead to disease.

By contrast, CNVs are overrepresented in genes that function in innate and acquired immunity and olfaction, and those that encode integral membrane proteins. Interestingly, these classes of gene match those that are predicted to require the ability to evolve particularly rapidly, for example, in response to altered host–pathogen interactions. Consistent with this, the authors found that the genes that contain CNVs have accumulated an unusually large number of substitutions that affect protein sequence, indicating that they have been subject to positive selection. CNVs could contribute to the ability to adapt by providing increased gene dosage, and therefore an adaptive advantage.

The search for structural variants has only recently begun, but many more are likely to be found. The findings from this study indicate that studying these variants closely will be important in understanding how humans have adapted to new environments.