The authors in their review of technological culture are proposing a series of unique human abilities that seem to distinguish humans from other animals. By doing this, they are following an unfortunate tendency to erect “Golden Barriers,” as said Stephen Jay Gould, to set us apart from the rest of the animal kingdom. This is commonly done with a simple trick: Namely, place the species compared with humans under unfavorable conditions (Allen Reference Allen2002; Bard & Leavens Reference Bard and Leavens2014; Rowe & Healy Reference Rowe and Healy2014). The result being that humans always fare better. Thus, the real “elephant in the room” is if this is science!

In their otherwise thorough review, the authors base all their comparative arguments on a few captive chimpanzee studies. Whenever they mention results on wild chimpanzees they regularly contradict them with captive experimental studies to which they give priority. Why is such a comparison unfair?

First, all leading hypotheses about the evolution of cognition have proposed the importance of ontogeny and socio-ecological factors. This is true for the ecological-intelligence hypothesis (Byrne Reference Byrne, Whiten and Byrne1997; Clutton-Brock & Harvey Reference Clutton-Brock and Harvey1980), the social intelligence (Dunbar Reference Dunbar1992; Humphrey Reference Humphrey, Bateson and Hinde1976), the cultural intelligence (Byrne & Whiten Reference Byrne and Whiten1989), as well as the eco-cultural hypotheses (Boesch Reference Boesch2007; Carpendale & Lewis Reference Carpendale and Lewis2004; Segall et al. Reference Segall, Dasen, Berry and Poortinga1999). Second, all studies evaluating the effects on cognition of the physical or social environment, as well as of experience, agreed to conclude that all these factors have a measurable positive effect on its development (e.g., Bard & Leavens Reference Bard and Leavens2014; Buchanan et al. Reference Buchanan, Grindstaff and Pravosudov2013; Fares et al. Reference Fares, Belmeguenai, Sanchez, Kouchi, Bodennec, Morales, Georges, Bonnet, Bouvard, Sloviter and Bezin2013; Hackman & Farah Reference Hackman and Farah2009; Lambourne & Tomporowski Reference Lambourne and Tomporowski2010; Leeuwen et al. Reference Leeuwen, Mulenga and Chidester2014; Middleton et al. Reference Middleton, Mitnitski, Fallah, Kirkland and Rockwood2008; Noble et al. Reference Noble, Houston, Brito, Bartsch, Kan, Kuperman, Akshoomoff, Amaral, Bloss, Libiger, Schork, Murray, Casey, Chang, Ernst, Frazier, Gruen, Kennedy, Van Zijl, Mostofsky, Kaufmann, Kenet, Dale, Jernigan and Sowell2015; Pike et al. Reference Pike, Ramsey and Wilkinson2018; Russell et al. Reference Russell, Lyn, Schaeffer and Hopkins2011; Sallet et al. Reference Sallet, Mars, Noonan, Andersson, O'Reilly, Jbabdi, Croxson, Jenkinson, Miller and Rushworth2011; Salvanes et al. Reference Salvanes, Moberg, Ebbesson, Nilsen, Jensen and Braithwaite2013; Thornton & Lukas Reference Thornton and Lukas2012; Toyoshima et al. Reference Toyoshima, Yamada, Sugita and Ichitani2018).

Figure 1 illustrates how two different cognitive traits, such as technical skills (trait 1, Sirianni et al. Reference Sirianni, Mundry and Boesch2015; Reference Sirianni, Wittig, Gratton, Mundry, Schuler and Boesch2018) or spatial knowledge (trait 2, Normand et al. Reference Normand, Ban and Boesch2009), could be affected by the ecological complexity in which the individual lives. The strongly limited access to objects in captivity has been shown to reduce the development of an understanding of the function of tools that could partially be improved with increased access to tools (see Bania et al. Reference Bania, Harris, Kinsley and Boysen2009; Furlong et al. Reference Furlong, Boose and Boysen2008), and will further be favored in the wild where tools are of a real value (Sirianni et al. Reference Sirianni, Mundry and Boesch2015; Reference Sirianni, Wittig, Gratton, Mundry, Schuler and Boesch2018). Although, spatial skills will remain very limited in captivity because of the strong space restriction of the environment (Premack & Premack Reference Premack and Premack1983), they can develop in the wild when foraging in kilometers-wide territories (Normand & Boesch Reference Normand and Boesch2009).

Figure 1.

The eco-cultural model for cognitive development: Four main factors have been shown to affect the development of cognition in animals, including age, ecological complexity, social, and cultural complexity. The potential effects of ecological complexity on two different cognitive traits when animals develop in traditional captive conditions (Ct), in environmental enriched captive conditions (Ce), or in the wild (W) are shown.

The chimpanzees studied by Povinelli and Tomasello cited extensively by the authors have for the first had only very limited access to objects in an artificial small peer-group without any adult models, whereas the second ones started in a medical research center subject to invasive experiments before experiencing better living conditions at the Leipzig zoo. As could have been expected both groups of chimpanzees show striking deficiencies in their understanding of tool function and integrity, notion of weight, space as well as in the social cognition, like the absence of cooperation and imitations (reviewed in Povinelli Reference Povinelli2000; Reference Povinelli2012; Tomasello Reference Tomasello2019b). Basing themselves on such human-shaped chimpanzees and rejecting field observations if they disagree with the formers, the authors built some nice dichotomy endorsing so-called human superiorities.

How would a fair comparison look like? What if free-ranging socially natural living chimpanzees were compared with humans living under similar conditions? In this way, natural differences would be identified to understand the evolution of human uniqueness. To restrict myself to technology, all chimpanzee groups studied throughout Africa use flexibly extended tool kits and often fashion the tools before use. Furthermore, they often plan the future needs of tools resulting in tool transports, with precise selection and/or modification of tools as a function of distance transported (Boesch & Boesch Reference Boesch and Boesch1983; Reference Boesch and Boesch1984; Reference Boesch and Boesch1990; Boesch et al. Reference Boesch, Head and Robbins2009; Estienne et al. Reference Estienne, Cohen, Wittig and Boesch2019a; Reference Estienne, Robira, Mundry, Deschner and Boesch2019b; Goodall Reference Goodall1968; Reference Goodall, Lehrmann, Hinde and Shaw1970; Luncz et al. Reference Luncz, Mundry and Boesch2012; Sanz & Morgan Reference Sanz and Morgan2007; Reference Sanz and Morgan2009; Sanz et al. Reference Sanz, Morgan and Gulick2004; Reference Sanz, Call and Morgan2009; Sirianni et al. Reference Sirianni, Mundry and Boesch2015; Reference Sirianni, Wittig, Gratton, Mundry, Schuler and Boesch2018; Sugiyama Reference Sugiyama1994; Sugiyama & Koman Reference Sugiyama and Koman1979). Mothers teach youngsters to stimulate the learning of tools in different populations of chimpanzees (Boesch Reference Boesch1991; Boesch et al. Reference Boesch, Bombjakova, Meier and Mundry2019; Musgrave et al. Reference Musgrave, Morgan, Lonsdorf, Mundry and Sanz2016; Reference Musgrave, Lonsdorf, Morgan, Prestipino, Bernstein-Kurtycz, Mundry and Sanz2020). None of these complex characteristics of tool use have been found in captive chimpanzees. Just one example, Taï chimpanzees select an optimal hammer out of an average of 16 available ones by considering five factors, including weight, hardness, distance to the anvil, and nut species, just by looking at them (Boesch & Boesch Reference Boesch and Boesch1984; Sirianni et al. Reference Sirianni, Mundry and Boesch2015) and this selection is condition-dependent on the distance to the nut-cracking site. This requires a complex form of conditional reasoning combining visible and imperceptible properties of the objects. New selections are repeated in numerous new situations throughout the 5 months of the two nut-cracking seasons (Sirianni et al. Reference Sirianni, Mundry and Boesch2015). Sure, in the forest, tools contribute to the survival of the animals, which is never the case in a captive environment. The value of captive experiments without any ecological validity has been amply critically discussed in the literature (e.g., Boesch Reference Boesch2012; Rowe and Healy Reference Rowe and Healy2014; Smulders et al. Reference Smulders, Gould and Leaver2010), but the authors seem not aware of this.

Comparisons with ecological and ontogenic validity would lead to totally different results than the target paper. As a reviewer of the paper, I informed the authors about the problem, but they were allowed by the journal to ignore this and perpetuating the simple trick to make humans look superior.