Cultural transmission and the capacity to approve or disapprove of offspring's behaviour

We suggest that human cultural learning was made possible by the simultaneous appearance, in one of our hominid ancestors, of two capacities the capacity to imitate others' behaviour and the capacity to approve or disapprove of others' behaviour. With the help of a mathematical model, we have studied the conditions that allow the evolution of both capacities. We consider four different genotypes "the only-learner" that learns by trial and error, "the imitator" that learns by trial and error and imitation, "the only-assessor" that learns by trial and error but that can also approve or disapprove of offspring's behaviour and, finally, "the assessor", who behaves like the imitator but, he can approve or disapprove of offspring's behaviour. The assessor genotype is the best genotype and the only-learner genotype is the worst when the learned behaviour that would be culturally transmitted is adaptive. If this behaviour is maladaptive, the genotype only-assessor is the best genotype and the genotype assessor can be the worst genotype. Notwithstanding, in this situation, the assessor can also be better than the imitator and even better than the only-learner. The success of assessor is due to his capacity to increase the phenotypic correlation between parents and offspring, and thus speeding the rate at which natural selection, if present, will increase or decrease the frequency of learned behaviours