Stibbard-Hawkes' comparative research challenges the assumed link between symbolic material evidence and behavioural modernity. We extend this approach to non-human species, focusing on common evidentiary criteria for human symbolic cognition (reviewed in Stibbard-Hawkes; see also Table 1 in the target article): Personal adornment, decoration, figurative art, and musical instruments. Our examination suggests that these standards might not effectively distinguish human from non-human animal behaviours, because they do not differentiate symbolic from non-symbolic cognition or because symbolic cognition is not uniquely human. This highlights the need for broader comparative perspectives.

Table 1 A non-comprehensive overview of proposed artefactual criteria (column 2) evidencing aspects of complex behaviour and cognition (column 1) adopted from Table 1 in Stibbard-Hawkes. Non-human animal evidence meeting these criteria (column 3) suggests that these archaeological standards may not accurately track uniquely human behavioural modernity and cognition, underscoring the need for broader comparative perspectives

Ochre use, an example of personal adornment interpreted as symbolic evidence in humans (e.g., d'Errico & Henshilwood, Reference d'Errico, Henshilwood, d'Errico and Henshilwood2011), is paralleled by birds' “cosmetic coloration” (Delhey, Peters, & Kempenaers, Reference Delhey, Peters and Kempenaers2007). Bearded vultures, for example, apply ochre to their bodies for status signalling, not utilitarian uses (Duchateau, Chéliz, Gil, & López-López, Reference Duchateau, Chéliz, Gil and López-López2022). Given their shared environments and practices, and since vulture evolution predates humans, it is possible that hominins copied this behaviour from these birds (Margalida, Almirall, & Negro, Reference Margalida, Almirall and Negro2023).

Non-utilitarian decorative objects or decorations of utilitarian artefacts are seen as symbolic as well (e.g., d'Errico & Henshilwood, Reference d'Errico, Henshilwood, d'Errico and Henshilwood2011). However, non-mammalian animals like spiders, insects, crustaceans, birds, and fish commonly use artefactual decoration for communication (Schaedelin & Taborsky, Reference Schaedelin and Taborsky2009). For example, male bowerbirds construct utilitarian objects (i.e., protective bowers) and decorate them with a diverse but selective collection of non-utilitarian objects, similar to ancestral hominin manuports. They also paint walls with processed vegetal residues (Hicks, Larned, & Borgia, Reference Hicks, Larned and Borgia2013), and even create theatres with forced perspective illusions, a technique humans only invented in the Renaissance (Endler, Endler, & Doerr, Reference Endler, Endler and Doerr2010).

Figurative art like figurines and representational rock art is considered a stringent and “unquestionable” criterion of uniquely human symbolic cognition, emerging as recently as 40–50 ka (Klein, Reference Klein2017, p. 213). However, as many animal species intentionally create resemblances to biotic and abiotic elements, non-human artefacts can also meet this criterion. For instance, wild orangutans create and cuddle “dolls” made of leaves (Bastian, Van Noordwijk, & Van Schaik, Reference Bastian, Van Noordwijk and Van Schaik2012; Laland, Reference Laland2017; Van Schaik, Van Noordwijk, & Wich, Reference Van Schaik, Van Noordwijk and Wich2006), and a captive dolphin calf imitated cigarette smoke with milk (Patterson & Mann, Reference Patterson, Mann, Kaufman and Kaufman2015). Vocal imitation, an acoustic equivalent of figurative art, is prevalent in cetaceans, pinnipeds, elephants, bats, songbirds, hummingbirds, and parrots (Verpooten, Reference Verpooten2021). This sophisticated cognition is an essential prerequisite for (spoken) language and is thus at least as relevant to symbolic cognition as figurative art (Jarvis, Reference Jarvis2019; Tyack, Reference Tyack2020). It is used by elephants, dolphins, and parrots to label and address individuals (King & Janik, Reference King and Janik2013; Pardo et al., Reference Pardo, Fristrup, Lolchuragi, Poole, Granli, Moss and Wittemyer2024; Scarl & Bradbury, Reference Scarl and Bradbury2009), and by lyrebirds to create a complex acoustic illusion of a mixed species mobbing flock (Dalziell, Maisey, Magrath, & Welbergen, Reference Dalziell, Maisey, Magrath and Welbergen2021). Unlike non-human primates, thousands of species exhibit vocal imitation, emphasizing the need for a broader comparative perspective in studying the evolution of symbolic cognition (Fitch, Reference Fitch2015; Tyack, Reference Tyack2020; Verpooten, Reference Verpooten2021).

If defined as non-bodily objects for acoustic communication, musical instruments are also not uniquely human. Many primates use objects for acoustic displays, such as branch shaking. Orangutans modify vocal displays using leaves. Percussive drumming in African great apes likely evolved in our common ancestor (Fitch, Reference Fitch2015). Chimpanzees drum on tree roots, producing signals similar to human drumming (Dufour, Poulin, Curé, & Sterck, Reference Dufour, Poulin, Curé and Sterck2015; Eleuteri et al., Reference Eleuteri, Henderson, Soldati, Badihi, Zuberbühler and Hobaiter2022) and amplify drumming with stones, creating rock accumulations akin to human cairns (Kühl et al., Reference Kühl, Kalan, Arandjelovic, Aubert, D'Auvergne, Goedmakers and Boesch2016).

Beyond primates, other mammals and birds, like woodpeckers, use non-bodily means for structured communicative sounds (Fitch, Reference Fitch2015). Narrowing the definition to manufactured instruments, male palm cockatoos use modified sticks or seedpods to drum on hollow trees during courtship displays, sharing key features with human instrumental music like rhythm and individual styles (Heinsohn, Zdenek, Cunningham, Endler, & Langmore, Reference Heinsohn, Zdenek, Cunningham, Endler and Langmore2017). This behaviour also exemplifies composite tool manufacture, a marker of cognitive complexity (Stibbard-Hawkes).

Extending Stibbard-Hawkes' critique, this artefactual evidence from diverse animals suggests that archaeological standards for human cognitive modernity may not exclude animal behaviours. Table 1 summarizes non-human evidence and the corresponding archaeological criteria. A broader comparative approach may clarify why this seems to be the case. One possibility is that these criteria ineffectively distinguish symbolic from non-symbolic cognition. Sophisticated artefacts may not need sophisticated cognition (reviewed in Stibbard-Hawkes). Figurative art, for example, could be accounted for by mere sensory manipulation, a common aspect of animal signalling dynamics (De Tiège, Verpooten, & Braeckman, Reference De Tiège, Verpooten and Braeckman2021; Verpooten & Nelissen, Reference Verpooten and Nelissen2010).

Alternatively, these evidentiary standards might indicate symbolic cognition, but the assumption that this is a uniquely human trait, let alone a tell-tale sign of human behavioural modernity, could be incorrect. Linguists often view recursion as a fundamental characteristic of language. When two syntactic objects are combined or “merged” to form a new syntactic unit, recursion implies that this merging can be applied to its own output, allowing for displaced reference (i.e., detachment from the immediate context), a hallmark of full symbolism (Planer, Reference Planer2021). Most non-human animal signals are “0-merge” systems without syntactic recombination (Suzuki & Zuberbühler, Reference Suzuki and Zuberbühler2019). However, some animals exhibit “1-merge” systems with basic compositional syntax (Suzuki, Wheatcroft, & Griesser, Reference Suzuki, Wheatcroft and Griesser2020). For instance, Japanese tits combine alert and recruitment calls into sequences for mobbing predators. Some animal communication systems, like cetaceans, may involve human-level “2-merge” and “3-merge” systems with recursive units, allowing for displaced reference and full symbolism (Allen, Garland, Dunlop, & Noad, Reference Allen, Garland, Dunlop and Noad2019; Andreas et al., Reference Andreas, Beguš, Bronstein, Diamant, Delaney, Gero and Wood2021; Cannon, Reference Cannon2023). Although animal symbolic cognition is not definitively demonstrated, research is progressing (Pepperberg, Reference Pepperberg, Call, Burghardt, Pepperberg, Snowdon and Zentall2017), aided by AI-assisted decoding of patterns in animal signalling (Andreas et al., Reference Andreas, Beguš, Bronstein, Diamant, Delaney, Gero and Wood2021; Pardo et al., Reference Pardo, Fristrup, Lolchuragi, Poole, Granli, Moss and Wittemyer2024).

In conclusion, the wide range of artefactual and communicative behaviours in different species challenges conventional criteria for uniquely human attributes and questions their absence in archaeological discourse. Our exploration advocates for a broader comparative approach in studying human cognitive origins, emphasizing its importance in identifying reliable archaeological indicators of uniquely human “modern” behaviour and symbolic cognition. For instance, the absence of vocal imitation ability, required for spoken language, in non-human primates and its presence in more distantly related taxa like cetaceans and parrots highlights this need. This discourse aims to open new pathways for understanding the evolution of human cognition and behaviour.