Use it or lose it

摘要

Limb modifications are fundamental to tetrapod evolution. Adaptive digit loss enables specialized functions such as running or flight, and has repeatedly evolved in parallel. But the developmental mechanisms underlying deviation from the five-digit ground state are unclear, partly owing to the hurdles involved in analysing embryos from animals that are not typically studied in the laboratory. Two papers published in this issue, from Cooper et al. (page 41) and Lopez-Rios et al. (page 46), illuminate developmental mechanisms that result in digit reduction in hoofed mammals and in rodents, and reveal surprising plasticity in the pathways that lead to evolutionary convergence. Together, these studies show that similar developmental changes may be shared by distantly related groups, but also that fundamentally different mechanisms can be used in closely related taxa to yield similar digit-loss outcomes.