Introduction

In the last decade, studies of parental care have rapidly proliferated. This increased interest in parental care has been stimulated by advances in three fields. First, the revolution in molecular biology has generated techniques that are increasingly used by behavioural scientists. Such techniques include DNA fingerprinting, which allows researchers to identify the genetic relatedness between putative parents and offspring, and molecular sex markers that allow researchers to determine the sex of offspring at an early stage before external differences have developed. In addition, gene sequencing, which is now fast and relatively inexpensive, has generated vast quantities of data, which are increasingly used to reveal evolutionary relationships that complement older morphology–based phylogenies. This has led to the second advance: several novel statistical techniques, which include parsimony and maximum–likelihood methods for phylogenetic reconstructions, have been developed to investigate past evolutionary events. These techniques provide new opportunities to examine the origins of parental care behaviour, the direction of parental care evolution and life history traits that may have influenced parental care evolution. Third, mathematical modelling of parental care has matured and now encompasses a range of game–theoretical models, some of which take account of state dependence and stochasticity. There has also been an effort to consider the feedback loops between parenting decisions and mating decisions. Some of these models were motivated by the growing consensus that parental care is one of the main battlefields for conflict between the sexes. New mathematical models have been essential in understanding aspects of these conflicts.