Teaching is a behaviour, or array of behaviours, that has provoked considerable debate (see Csibra Reference Csibra2007; Hoppitt et al. Reference Hoppitt, Brown, Kendal, Rendell, Thornton, Webster and Laland2008; Premack Reference Premack2007; Thornton & Raihani Reference Thornton and Raihani2008). Much of this debate comes from the belief that teaching is a behaviour that requires uniquely human cognitive abilities, such as theory of mind, and therefore occurs only in humans (Premack Reference Premack2007). A number of supporters of the mentalistic and culture-based approaches to teaching argue that there is remarkably little evidence for teaching in nonhuman animals, and supporters of the functionalist approach agree (Byrne et al. Reference Byrne, Sanz, Morgan, Sanz, Call and Boesch2013; Thornton & Raihani Reference Thornton and Raihani2008; Reference Thornton and Raihani2010). However, the way that teaching is defined is likely to be a primary cause for the relative absence of it in nonhuman animals (Thornton & Raihani Reference Thornton and Raihani2010). Indeed, a recent surge in research claiming to show teaching in nonhuman animals has benefited strongly from the functionalist definitions proposed by Caro and Hauser (Reference Caro and Hauser1992) and updated by Hoppitt et al. (Reference Hoppitt, Brown, Kendal, Rendell, Thornton, Webster and Laland2008). By providing a definable criteria for what constitutes teaching, within a quantifiable and comparative framework, teaching has now been discovered in a number of animals (for recent examples, see Franks & Richardson Reference Franks and Richardson2006; Kleindorfer et al. Reference Kleindorfer, Hoi, Evans, Mahr, Robertson, Hauber and Colombelli-Négrel2014; Raihani & Ridley Reference Raihani and Ridley2008; Thornton & McAuliffe Reference Thornton and McAuliffe2006; and see Maestripieri et al. [Reference Maestripieri, Ross and Megna2002] and others reviewed in Thornton & Raihani [2008] for anecdotal examples of teaching in animals that have not yet been experimentally proven).

Teaching, if we are to follow the functionalist definition, may therefore not be as rare as originally supposed. Indeed, Byrne et al. (Reference Byrne, Sanz, Morgan, Sanz, Call and Boesch2013) argue that “the old idea that cultural learning through teaching is how we do things, while trial-and-error fumbling is how animals do them has now been thoroughly discredited” (p. 51 [emphasis in original]).

Even from the perspective of human-based studies it has become increasingly acknowledged that the mentalistic and culture-based definitions of teaching are overly restrictive. For example, recent research into the occurrence of teaching behaviour in humans has used nonhuman examples to explain the different types of teaching that exist (Dean Reference Dean2011; Niedermeyer Reference Niedermeyer2014). The famous philosopher John Dewey wanted to ground our understanding of teaching in evolutionary theory, and hence came up with a definition of the two types of teaching – which is very similar to that of Thornton and Raihani (Reference Thornton and Raihani2008). However, Dewey failed to make the explicit link between the evolutionary bases of teaching behavior and human education (Niedermeyer Reference Niedermeyer2014). Thus, Kline's article provides welcome recognition of the need for a unification of the definition of teaching in her call for a new, evolutionary framework for teaching.

Previously, it has been suggested that teaching must be defined in the absence of environmental and genetic influences (reviewed in Dean Reference Dean2011). However, increasing opposition to this idea identifies that environmental factors are likely to influence behavioural patterns in all animals, and to exclude them would result in false negatives (Laland & Janik Reference Laland and Janik2006). Therefore, while we agree with Kline that a new framework for the definition and measurement of teaching behaviour is required, we disagree with the following statement:

This suggests that humans act as the benchmark for understanding the occurrence of teaching in other animals. While it may be the case that humans are abnormally prolific teachers for certain types of teaching behaviour, this does not explain why teaching behaviour may be present in other animals. In all cases, if teaching creates a benefit for both teacher and pupil (albeit a delayed benefit for the teacher), if the cost of teaching is not prohibitively high for the teacher, and learning would not have occurred (or occurred less efficiently) in the absence of teaching, then teaching may be expected to occur (Fogarty et al. Reference Fogarty, Strimling and Laland2011). It is therefore unclear to us why the occurrence of teaching in humans should be used as a benchmark to explain teaching in nonhuman animals. Indeed, even those opponents to the evidence of teaching in nonhuman animals suggest that the key differences are in the type of teaching that occurs, rather than the existence of teaching at all (Csibra Reference Csibra2007; Premack Reference Premack2007).

Kline suggests that without a common framework to compare between humans and other animals, the functionalist framework (the framework primarily used in nonhuman animal studies) may only provide part of the explanation for why teaching evolves in many species. While we understand Kline's point of view here – that the apparently atypical and sophisticated teaching behaviors in humans are an interesting case – it does not mean that we should assume that the factors that promoted this apparently “abnormal” teaching in humans explains the occurrence of teaching in other species. Instead, we suggest it is highly likely that teaching has arisen as a survival and/or fitness benefit according to the prevailing ecological and social conditions that species are exposed to. If we start at a point where we agree upon a clear definition of teaching that does not require uniquely human behaviours, but instead focuses upon what really constitutes teaching behaviour, then we may truly create a framework where a unified, operational definition for teaching can be quantified and thus compared between studies.