Scientific progress is made by revealing new causal connections at various levels of depth and detail. Several articles in this issue discuss technical advances in mapping large- and small-scale relationships, leading to the discovery of new connections and structural or functional principles, and improving predictive abilities.

Kevin Foster's review (p193) attempts to heal the 50-year-long rift between sociobiology and molecular biology. He illustrates how the forces that underlie social evolution — competition and cooperation — are equally good at shaping form and function at all levels of biological organization, from gene structure to metabolism to multicellularity. Also, a recent intriguing paper (In Brief, p156), highlights another type of social interaction between genotypes: in humans, alleles at certain loci correlate with connections in a social network.

Two other Reviews touch on relationships on another level — those between genotype and phenotype. In an addition to our article series on 'Fundamental Concepts in Genetics', Wagner and Zhang (p204) examine the technical and conceptual challenges in defining and measuring pleiotropy, and how the realization that pleiotropy is more restricted than once assumed affects disease mapping and our view of evolvability.

Kayser and de Knijff (p179) take genotype–phenotype mapping into the applied area of forensic DNA profiling. Among various technical advances afforded by the use of SNPs, the authors discuss the growing success in using DNA profiles to reconstruct a person's biogeographic ancestry or to estimate their externally visible characteristics, such as hair, eye or skin colour.

These broad-ranging articles also highlight the increasing use of interdependent data sets gathered across disciplines to infer general principles of biological patterns.