Suberin-related bands identified with FTIR are unreliable to differentiate Neanderthal tar production strategies

Abstract

The use of adhesives in Middle Pleistocene hominin tool technology represents a significant technological advance. As early as 200,000 years ago, Neanderthals utilized fire to produce birch bark tar. A recent study proposed underground birch bark tar production, identified by FTIR analysis, indicates evidence of Neanderthal cumulative culture. However, we evaluated new FTIR spectra of experimental birch bark tar and found discrepancies in the proposed link between suberin and underground tar production. Our experiments, replicating condensation, pit roll, and raised structure methods, demonstrate the sensitivity of birch bark tar composition to small production variables. Highly similar condensation production experiments yielded tars with varying peak heights associated with SiO2 and suberin. This can skew results of principal component analyses and shows suberin bands are not unique to tar produced underground. This challenges previous assertions and emphasizes the need to consider production variables and post-depositional influences. While the patterns identified by previous research are intriguing, our study underscores the importance of accounting for biomolecular variability in birch bark tar to securely identify production methods based on FTIR analysis.