Abstract
The zone of latent solutions (ZLS) hypothesis provides an alternative approach to explaining cultural patterns in primates and many other animals. According to the ZLS hypothesis, non-human great ape (henceforth: ape) cultures consist largely or solely of latent solutions. The current competing (and predominant) hypothesis for ape culture argues instead that at least some of their behavioural or artefact forms are copied through specific social learning mechanisms (“copying social learning hypothesis”) and that their forms may depend on copying (copying-dependent forms). In contrast, the ape ZLS hypothesis does not require these forms to be copied. Instead, it suggests that several (non-form-copying) social learning mechanisms help determine the frequency (but typically not the form) of these behaviours and artefacts within connected individuals. The ZLS hypothesis thus suggests that increases and stabilisations of a particular behaviour’s or artefact’s frequency can derive from socially-mediated (cued) form reinnovations. Therefore, and while genes and ecology play important roles as well, according to the ape ZLS hypothesis, apes typically acquire the forms of their behaviours and artefacts individually, but are usually socially induced to do so (provided sufficient opportunity, necessity, motivation and timing). The ZLS approach is often criticized—perhaps also because it challenges the current null hypothesis, which instead assumes a requirement of form-copying social learning mechanisms to explain many ape behavioural (and/or artefact) forms. However, as the ZLS hypothesis is a new approach, with less accumulated literature compared to the current null hypothesis, some confusion is to be expected. Here, we clarify the ZLS approach—also in relation to other competing hypotheses—and address misconceptions and objections. We believe that these clarifications will provide researchers with a coherent theoretical approach and an experimental methodology to examine the necessity of form-copying variants of social learning in apes, humans and other species.
Highlights
Despite the continuously growing body of research on the behavioural repertoires of non-human great apes (: apes), the necessary mechanisms behind the acquisition of their various behavioural and artefact forms1 are still a matter of debate
For more complex behaviours, such as chimpanzee nutcracking this approach would only require one single reinnovation to make the claim that the behavioural form is in the zone of latent solutions (ZLS) of the species, as these behaviours should be less likely to have been reinnovated by chance
According to the ape ZLS approach, individual and social learning work in conjunction65 to create an illusion of a spread in ape cultures, where the resulting forms remain individually derived and lack cultural evolution
Summary
Despite the continuously growing body of research on the behavioural repertoires of non-human great apes (: apes), the necessary mechanisms behind the acquisition of their various behavioural and artefact forms are still a matter of debate. Several captive primate populations (that had likely not observed the nut-cracking behavioural form) “reinnovated” nut-cracking in experimental studies (Visalberghi 1987; Marshall-Pescini and Whiten 2008; Bandini et al, in review; but see Boesch 1996) Taken together, these instances of copying-independent (re-)innovations of the underlying form suggest that social learning, of any type (including copying, such as imitation), may not be necessary for the acquisition of the form of nut-cracking by individual chimpanzees, the geographic pattern (as with the Neesia tool use in wild orangutans: van Schaik 2009) indicates that its’ innovation is not easy and may take a long time. In 2009, Tennie et al, proposed such an alternative account: the zone of latent solutions (ZLS) hypothesis Whilst this approach can be used to potentially explain culture in any animal species (though it may not fit every culture), the more specific “ape ZLS hypothesis” states that ape culture arises—and is maintained—by social learning variants that do not produce copies of behavioural forms (i.e., nonform-copying social learning, : “non-copying”). This would be in stark contrast to the majority of modern human cultural behavioural (and artefact) forms, which, arguably, depend on copying (culturedependent traits, Reindl et al 2017; or, what we refer to here as: copying-dependent forms). Copied form is of high importance to human culture
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