Imagine if we had attempted to define the uniqueness of human social cognition in the year 2000. Investigations examining primate theory of mind had started more than 30 years before. Despite this, researchers had still not developed experimental paradigms with sufficient ecological validity to thoroughly test the cognitive abilities of primates. We would have concluded that there was a large gap between human and ape social cognition. Hare et al.'s seminal work (Reference Hare, Call and Tomasello2001), where chimpanzees were put into competitive situations rather than cooperative ones, suggests that they can take the perspective of others, though as always, this conclusion is controversial (see Vonk & Povinelli Reference Vonk, Povinelli, Wassermann and Zentall2006). This work has been built on in the past 10 years, with a number of novel paradigms being designed, where, for example, food must be stolen from others or an ape must infer which food item another individual has eaten (see Call and Tomasello Reference Call and Tomasello2008 for review). Because of the high level of behavioral sophistication uncovered by these recent findings, it is now possible to make a case for the gap between human and ape social cognition being far smaller than previously thought (Call and Tomasello Reference Call and Tomasello2008; Schmelz et al. Reference Schmelz, Call and Tomasello2011; but see Penn & Povinelli Reference Penn and Povinelli2007b; Penn et al. Reference Penn, Holyoak and Povinelli2008).

What research on social cognition teaches us is that we have to be careful that our paradigms are sufficiently fine tuned and ecologically valid before drawing strong conclusions.

Is the trap-tube, the current paradigm predominantly used in physical cognition tests (and discussed by Vaesen in the target article), sufficient for drawing conclusions about animals? We suggest not. The trap-tube problem requires an animal to extract food from an apparatus while avoiding a trap in its surface. Slight changes to this test, such as whether an animal is allowed to pull food out of the tube, leads to differences in performance at test, and consequently, the conclusions drawn about what the animal understands (Mulcahy & Call Reference Mulcahy and Call2006a).

Furthermore, whereas great apes do fail to transfer information between the trap-tube and trap-table tasks while using tools, the same pattern is not seen when they do not need a tool and can instead use their own finger (Seed et al. Reference Seed, Call, Emery and Clayton2009). It appears, then, that the tool-use aspect of the trap-tube problem creates an additional cognitive load that interferes with problem solving. Most important, adult humans fail to solve a control condition where the trap-tube is inverted (Silva et al. Reference Silva, Page and Silva2005). Given that objects only fall down and not up, an animal that understands why the trap works should treat an upside-down trap as non-functional. In contrast, an animal that has associatively learnt to avoid the trap should continue to avoid it, irrespective of its position in the tube. Adult humans, however, make the striking error, as some animals have done (e.g., Visalberghi & Limongelli Reference Visalberghi and Limongelli1994), of continuing to avoid the trap when it is in the upside-down position. In contrast, apes, woodpecker finches, and New Caledonian crows do not avoid the trap in an inverted tube (Mulcahy & Call Reference Mulcahy and Call2006a; Taylor et al. Reference Taylor, Hunt, Medina and Gray2009a; Reference Taylor, Hunt, Roberts and Gray2009b; Tebbich & Bshary Reference Tebbich and Bshary2004).

It seems premature to draw strong conclusions about the absence of inferential causal reasoning abilities from a test that seems to be confounded by tool use and solved incorrectly by adult humans.

Claims about human uniqueness also need to consider evidence from evolutionary convergence. There is no reason why distantly related species facing similar socio-ecological challenges as humans were could not have evolved cognitive mechanisms lacked by species more closely related to humans. Imagine if we had stopped the clock in 1995 and attempted then to draw a line between humans and animals. At that point in time we would have thought that wooden hook tools, experience projection, and planning for tomorrow were capacities exclusive to humans. The reason for this is that few scientists had investigated the possibility that convergent evolution may have led birds to have evolved complex behaviors and cognition.

Today, evidence from work on the Corvidae family has shown that New Caledonian crows can manufacture hook tools by sculpting wood (Hunt Reference Hunt1996; Hunt & Gray Reference Hunt and Gray2004) and can spontaneously solve multi-stage metatool problems (Taylor et al. Reference Taylor, Elliffe, Hunt and Gray2010), while scrub-jays have been shown to recall the past (Clayton & Dickinson Reference Clayton and Dickinson1998) and plan for tomorrow (Raby et al. Reference Raby, Alexis, Dickinson and Clayton2007). In the social sphere, ravens engage in play caching to identify thieves (Bugnyar et al. Reference Bugnyar, Schwab, Schloegl, Kotrschal and Heinrich2007), and only scrub-jays with experience of stealing food engage in sophisticated cache-protection strategies (Emery & Clayton Reference Emery and Clayton2001). The only non-human evidence for experience projection and hook tool manufacture in the wild comes from corvids, as does the strongest evidence for future planning. Finally, although apes cannot transfer knowledge between the trap-tube and trap-table while using tools, New Caledonian crows can (Taylor et al. Reference Taylor, Hunt, Medina and Gray2009a).

Evidence from convergent evolution, therefore, needs to be considered if we are to draw the right conclusions about human uniqueness. As the results from the trap-tube exemplify, failure of the great apes on a cognitive task does not mean that no other animal will succeed. We simply do not yet know if, for example, New Caledonian crows have diagnostic learning. It may seem unlikely that a species with a brain the size of a walnut may be capable of such cognition, but then in 1995, who would have predicted that members of the crow family would manufacture wooden hook tools or plan for the future?

This is not to say that we disagree with attempts to draw conclusions about what cognition is used by humans during tool use, or with the highlighting of how weak the single-factor argument for human uniqueness is. In contrast, summarizing the field to date and suggesting the potential boundaries between humans and other animals in the tool domain will drive and focus research effort on understudied areas, such as diagnostic learning and functional representation. Our cherry-picking mental time travel is simply to highlight that much may change in the future. Who knows where the boundaries will lie in 10 years time.