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Do early stone tools indicate a hominin ability to accumulate culture?

Periodic Reporting for period 3 - STONECULT (Do early stone tools indicate a hominin ability to accumulate culture?)

Reporting period: 2020-04-01 to 2021-09-30

What is culture? Culture requires at least one variant of a “social learning” mechanism to influence at least the frequency – or even the form (the specific design) – of behaviors or artefacts in a population. Previous research has argued that similar social learning mechanisms underlie modern human and early hominin technology. However, early hominin culture shows periods of stasis, where modern human culture is instead cumulative. This cumulative culture is powered and enabled by special variants of social learning mechanisms – namely those that can copy forms. Form copying even necessarily leads to cumulative culture. This in turn leads to path-dependent form changes and, eventually, to a complete dependency of the resulting form variants on copying (so-called culture-dependent forms). The assumption of the presence of copying skills therefore is completely at odds with the observed patterns of stasis for early stone tools.

Instead of copying forms from others (as modern humans do), ape cultures are based on non-copying variants of social learning. These variants still produce cultural patterns as they mediate the relative frequencies of forms between populations. Yet. ape cultures are based on and fuelled by "socially mediated individual reinnovations" instead of copying. These reinnovations derive not from path-dependent copying, but are forms that ape can in principle recreate on their own (so-called latent solutions; Tennie et al. 2009, Phil Trans B). Again, unlike copying, socially mediated individual reinnovation do not lead to path-dependency or culture-dependent forms. The latent solutions approach is a core candidate to account for early hominin stone tools because it provides an actual explanation for the stasis observed in the early stone tool archaeological record. It also is not at odds with what is actually known about apes & it alone does not require additional, unproven ad-hoc assumptions (such as extreme conformity).

Using both a general triangulation of the question, STONECULT tests whether early stone tools may be most parsimoniously regarded as manifestations of cumulative culture or whether they are best accounted for by latent solutions. STONECULT evaluates whether early stone tools were more similar either to modern ape (i.e. restricted to latent solutions) or modern human technologies (i.e. path-dependent cumulative culture, based on copying). STONECULT will help to pinpoint when cumulative culture first started in our lineage.

STONECULT uses a triangulation approach designed to provide the first empirical test for the latent solution hypothesis on the earliest stone tools (flake production methods and accompanying stone tool and stone core forms). This is a feasible task as the latent solution method applied in STONECULT has already uncovered latent solutions in all phylogenetically close groups: modern apes. STONECULT tests for latent solutions underlying early stone tools across three objectives/approaches (Objective 1, testing apes; Objective 2, testing modern humans). Objective 3 tests for the unintentional, automatic production of early stone tool forms via the unsupervised outputs of a "virtual knapper" software program.
The theoretical foundation to test socially mediated indivdual reinnovations in early stone tools (the target of STONECULT) was published as a Forum Article in Current Anthropology: The article made clear the alternative to the current null hypothesis for early stone tools (the current null being that early stone tool forms were and had to be copied). This alternative view - the zone of latent solutions view - posits a discontinuity between apes (and early hominins) versus modern humans. This discontinuity is posited for social learning mechanisms - where apes and early hominins have socially mediated individual reinnovation, modern humans have copying (Tennie et al. 2017 Current Anthropology). We also continue to respond to publications that argue one way or another with regards to the question (e.g. Tennie 2019 in Current Anthropology - plus several MS in preperation).

Objective 1. We have submitted our first ape manuscript (Objective 1) - with several more in preparation.

Objective 2. After a successful pilot test we imminently (in 2019) will start testing human participants for Objective 2.

Objective 3. As expected, the production of the virtual knapper software takes extended efforts. However, we have made good progress. In addition, we have identified a new approach that we are now exploring in parallel. Therefore, Objective 3 (virtual knapper) now has not one, but two independent chances of success.
Expected results until the end of the project:

Objective 1: Based on the available results (submitted as well as in preparation), we expect to change the current thinking of ape abilities to produce and use sharp stone flakes.

Objective 2: Any outcome (positive or negative) of the humans tests will be directly interpretable, and will therefore be of high impact for current thereotical approaches and future methodologies used in experimental archaeology.

Objective 3: Given that we have identified an entirely new approach to create a virtual knapper, we have doubled the chances for success. Once at least one virtual knapper approach works, it will be checked for its reliability and validity - and once it passes both checks, it will be used for experimentation for the automatic production of early stone tool shapes (without any need for copying).

Overall, we also plan to write at least one synthesis paper across all three objectives.

Progress beyond the state of the art:

We have clarified the theoretical position that, in a minimal sense, culture merely equals social learning (Neadle et al. 2017, PLoS ONE; Tennie et al. in press; Tennie et al. submitted).

We have also explored additional possible reasons for the discontinuity between ape/hominin and human culture - in particular, a potential lack of motivation to teach others and a lack of curiosity (van Schaik et al. 2019 in Behavioral Ecology and Sociobiology).

As for empirical data, new findings for latent solutions in apes have been published (Bandini & Tennie 2019, AJP; Neadle et al. 2017, PLoS ONE - plus several MS in preparation). Two particular cases to highlight are 1) that chimpanzees can spontaneously reinnovate "digging sticks" (Motes-Rodrigo et al. 2019 PLoS ONE) and that 2) a feasible production method for "birch bark tar" could have been a latent solution for Neanderthals (Schmidt et al. 2019 PNAS; Schmidt et al. under review). That is, neither of these artefacts can remain good evidence for cumulative culture and its neccessary social learning mechanisms.

We are also engaged in computer modelling of wild ape cultural patterns (Acerbi, Snyder & Tennie, in prep.). As predicted, the results of these models demonstrate that ape cultural patterns can and do indeed arise without any copying variants of social learning mechanisms neccessary.

Multiple further studies are in a planning stage, are already run or being written up (e.g. tests for action copying in apes; tests for reinnovation of nutcracking behaviour in apes; re-analysis of stone tool shapes; opinion piece on animal reinnovation; preditive modelling of core shapes etc etc). We also did a review of behaviour and artefact production across all wild ape populations (Motes-Rodrigo & Tennie, in prep.)-