Evolution of animal regeneration: re-emergence of a field.

Regeneration, the replacement of lost body parts, is widespread yet highly variable among animals. Explaining this variation remains a major challenge in biology. Great strides have been made in understanding the phylogenetic distribution, ecological context and developmental basis of regeneration, and these new data are yielding novel insights into why and how regeneration evolves. Here, we review the phylogenetic distribution of regeneration and discuss how the origin, maintenance and loss of regeneration can each be driven by distinct factors. As the complexity of factors affecting regeneration evolution is increasingly appreciated, and as explicitly evolutionary studies of regeneration become more common, the coming years promise exciting progress in revealing the underlying mechanisms that have shaped animal regeneration.