Vaesen has produced a convincing descriptive account of the unique cognitive abilities that support human-style tool use. The icing on the cake would be to explain how those abilities may have evolved. What were the selection pressures that made tool-using hominid minds different from the minds of other tool-using species? Washburn suggested the answer to this question more than 50 years ago:
Tools changed the whole pattern of life[,] bringing in hunting, cooperation, and the necessity for communication and language. Memory, foresight and originality were favored as never before, and the complex social system made possible by tools could only be realized by domesticated individuals. In a real sense, tools created Homo sapiens. (Washburn Reference Washburn1959, p. 31)
A process of technological selection would operate when the use of a tool enhances the tool user's fitness. A dependency on tools that conferred fitness advantages may have arisen as hominid ancestors became stranded in increasingly drier open landscapes that offered few places to hide from predators. Even before scrounging for food or having sex, the most important thing those hominids could have done was to protect themselves from being killed and eaten. The solutions they developed to this survival problem would have been under strong selection pressure (Hart & Sussman Reference Hart and Sussman2005), and data on modern cases of wild animal attacks on humans indicate that using tools as weapons would have been a very good solution. In a study of 542 animal attacks occurring on all continents, Crabb and Elizaga (Reference Crabb and Elizaga2008) found that when victims or passersby used any of 65 different tools to defend against attacking animals, injuries and deaths were significantly lower than when no tools were used. Smart tool use saves human lives in the present, and very likely would have saved the lives of hominid ancestors. One cognitive legacy of this ancestral dependence on tools for protection (albeit not mentioned by Vaesen) may be a preparedness in modern humans to associate aggressive impulses with tools that could be used as weapons (Crabb Reference Crabb2000; Reference Crabb2005; Kenrick & Sheets Reference Kenrick and Sheets1993).
Hominid ancestors who clutched sticks and stones to guard against predators wherever they roamed would have gotten to know their tools quite well. Those individuals with sufficient variants in cognitive abilities would have experimented with and elaborated upon their tools, eventually hitting on the invention of true tools (i.e., tools made by using other tools; Gruber Reference Gruber1969) that would have provided even more survival benefits and additional cognitive and technical challenges.
The differential survival of adept tool users would have contributed to the growth of tool-using culture. A tool-dense culture would in turn influence which genes were subject to selection, and genes that supported the cognitive architecture for sophisticated tool use would be favored (see Laland et al. Reference Laland, Odling-Smee and Feldman2000; Richerson & Boyd Reference Richerson and Boyd2005). Darwin seemed to have had just this kind of gene-culture coevolutionary process in mind:
We can see that, in the rudest state of society, the individuals who were the most sagacious, who invented and used the best weapons or traps, and who were best able to defend themselves, would rear the greatest number of offspring. The tribes which included the largest number of men thus endowed would increase in number and supplant other tribes. (Darwin Reference Darwin1871/1981, p. 159)
In this way, the life-saving technological way of life constructed only by human ancestors would have selected the cognitive tunings described by Vaesen.
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Vaesen has produced a convincing descriptive account of the unique cognitive abilities that support human-style tool use. The icing on the cake would be to explain how those abilities may have evolved. What were the selection pressures that made tool-using hominid minds different from the minds of other tool-using species? Washburn suggested the answer to this question more than 50 years ago:
Tools changed the whole pattern of life[,] bringing in hunting, cooperation, and the necessity for communication and language. Memory, foresight and originality were favored as never before, and the complex social system made possible by tools could only be realized by domesticated individuals. In a real sense, tools created Homo sapiens. (Washburn Reference Washburn1959, p. 31)
A process of technological selection would operate when the use of a tool enhances the tool user's fitness. A dependency on tools that conferred fitness advantages may have arisen as hominid ancestors became stranded in increasingly drier open landscapes that offered few places to hide from predators. Even before scrounging for food or having sex, the most important thing those hominids could have done was to protect themselves from being killed and eaten. The solutions they developed to this survival problem would have been under strong selection pressure (Hart & Sussman Reference Hart and Sussman2005), and data on modern cases of wild animal attacks on humans indicate that using tools as weapons would have been a very good solution. In a study of 542 animal attacks occurring on all continents, Crabb and Elizaga (Reference Crabb and Elizaga2008) found that when victims or passersby used any of 65 different tools to defend against attacking animals, injuries and deaths were significantly lower than when no tools were used. Smart tool use saves human lives in the present, and very likely would have saved the lives of hominid ancestors. One cognitive legacy of this ancestral dependence on tools for protection (albeit not mentioned by Vaesen) may be a preparedness in modern humans to associate aggressive impulses with tools that could be used as weapons (Crabb Reference Crabb2000; Reference Crabb2005; Kenrick & Sheets Reference Kenrick and Sheets1993).
Hominid ancestors who clutched sticks and stones to guard against predators wherever they roamed would have gotten to know their tools quite well. Those individuals with sufficient variants in cognitive abilities would have experimented with and elaborated upon their tools, eventually hitting on the invention of true tools (i.e., tools made by using other tools; Gruber Reference Gruber1969) that would have provided even more survival benefits and additional cognitive and technical challenges.
The differential survival of adept tool users would have contributed to the growth of tool-using culture. A tool-dense culture would in turn influence which genes were subject to selection, and genes that supported the cognitive architecture for sophisticated tool use would be favored (see Laland et al. Reference Laland, Odling-Smee and Feldman2000; Richerson & Boyd Reference Richerson and Boyd2005). Darwin seemed to have had just this kind of gene-culture coevolutionary process in mind:
We can see that, in the rudest state of society, the individuals who were the most sagacious, who invented and used the best weapons or traps, and who were best able to defend themselves, would rear the greatest number of offspring. The tribes which included the largest number of men thus endowed would increase in number and supplant other tribes. (Darwin Reference Darwin1871/1981, p. 159)
In this way, the life-saving technological way of life constructed only by human ancestors would have selected the cognitive tunings described by Vaesen.