The Oldowan knapped stone industry appeared around 2.6 million years ago. Given a lack of evidence for trial and error in Oldowan knapping (De La Torre Reference De La Torre2004; Delagnes & Roche Reference Delagnes and Roche2005) some teaching may have underpinned the transmission of this technology. However, the technology and shape of Oldowan artefacts was largely controlled by the properties of the raw materials used, rather than by stylistic traditions (De La Torre Reference De La Torre2004; Toth Reference Toth1985). If teaching were to have occurred, it likely only needed to be what Kline defines as “lower-effort forms.” It is not until 1.75 million years ago, with the emergence of the Acheulean industry, that we see a shift in lithic construction hinting at the onset of Kline's “higher-effort forms of teaching.”
Acheulean technology involved the ability to strike large stone flakes and bifacially shape stone artefacts into hand-axes and cleavers (Beyene et al. Reference Beyene, Katoh, WoldeGabriel, Hart, Uto, Sudo, Kondo, Hyodoi, Renne, Suwa and Asfaw2013; Lepre et al. Reference Lepre, Roche, Kent, Harmand, Quinn, Brugal, Texier, Lenoble and Feibel2011). Consider cleaver manufacture from the 1.21 million year-old site of Isampur Quarry in South India (Shipton Reference Shipton2013). Cleavers are U-shaped bifaces with a broad bit as their principal cutting edge, manufactured by setting up platforms on thick slabs of limestone from which large flakes could be struck obliquely to the bedding plane, then retouched into the requisite shape (Petraglia et al. Reference Petraglia, LaPorta and Paddayya1999; Shipton et al. Reference Shipton, Petraglia and Paddayya2009). The manufacturing sequence involves several hierarchically organized stages, such as removing thick flakes from the slab perimeter to set up suitable platforms from which to strike the large blank flakes; and to a novice it would be unclear how some of these relate to the finished product (Shipton Reference Shipton2013). To understand why the platform is necessary requires sufficient experience to accurately identify the angles and surfaces that are good for striking large flakes. It is also important to note that Acheulean hand-axes and cleavers are deliberately shaped to be symmetrical, often in two planes (Wynn Reference Wynn2002), yet butchery experiments suggest that this symmetry may not greatly improve their utilitarian value (Machin et al. Reference Machin, Hosfield and Mithen2007). In other words, they feature unnecessary characteristics and were probably made using unnecessary processes. Demonstrating the requisite skills may have required one of Kline's higher forms of teaching in order to steer novice knappers to the same, somewhat arbitrary, outcomes.
But it is here that we are confronted with a conundrum that highlights a key aspect of the human condition missed by Kline. The Acheulean period stands out for its unparalleled homogeneity: The industry persists for around 1.5 million years (Shipton et al. Reference Shipton, Clarkson, Pal, Jones, Roberts, Harris, Gupta, Ditchfield and Petraglia2013). Compare this to a state-of-the-art personal computer purchased 10 years ago that is now so obsolete it is probably best employed as a piece of kitsch sculpture. Signs of cumulative culture in the Acheulean are, therefore, fleeting. What, then, is missing? The answer is hidden in Kline's target article. She is rightly at pains to point out that her examples of teaching are just that, and should not be taken as prescriptive. But note a key aspect of each example where humans are involved: All feature adult to child transmission, something that cannot occur if there are no children.
Due to the large size of our brain, but relatively narrow birth canal, humans are born in a state of altriciality where they depend on their parents for nourishment for longer than most animals (Bogin Reference Bogin and Panter-Brick1998). With the high metabolic demands of a brain that is still growing rapidly, humans have evolved “childhood,” a new life history stage in which older members of the social group provide specially prepared foods that are high in energy and nutrients for the young whose brains are growing rapidly, but whose bodies are growing slowly (Kaplan et al. Reference Kaplan, Hill, Lancaster and Hurtado2000; Locke & Bogin Reference Locke and Bogin2006). No other living species has this. Indeed, it may not have appeared until relatively late in our evolutionary history.
Reconstructions of extinct hominin life history using dental development, body mass, and brain growth point to a short or absent childhood in the earlier Acheulean hominin Homo erectus (for summaries, see Nielsen Reference Nielsen2012b; Robson & Wood Reference Robson and Wood2008). Childhood as we know it thus post-dates the emergence of Acheulian stone tools (Hopkinson et al. Reference Hopkinson, Nowell and White2013). In contrast, there is evidence of a childhood in Homo neanderthalensis (Smith et al. Reference Smith, Toussaint, Reid, Olejniczak and Hublin2007) who are, along with early Homo sapiens, associated with the establishment of Middle Paleolithic technology around 300,000 years ago. It is during the Middle Paleolithic that, under the right demographic circumstances, we begin to see instances of cumulative cultural evolution (d'Errico & Stringer Reference d'Errico and Stringer2011; Powell et al. Reference Powell, Shennan and Thomas2009). Notably, by the Late Acheulean period a handful of technological advances, such as the use of soft-hammers, had accrued (Stout et al. Reference Stout, Apel, Commander and Roberts2014), and there is evidence that the Late Acheulean hominin Homo heidelbergensis had childhood lengths more similar to our own than Homo erectus (Nowell & White Reference Nowell, White, Nowell and Davidson2012; Robson & Wood Reference Robson and Wood2008).
Childhood enables ample opportunity for play and discovery, and for entertaining the kinds of creativity that later in life undergird the imaginative endeavours that may bring new technological advances (Nielsen Reference Nielsen2012a; Reference Nielsen2012b). Childhood also affords multiple opportunities for extensive learning and for sophisticated cultural behaviors to arise (Bogin Reference Bogin1990) – and hence for more complex and detailed approaches to teaching. Childhood is necessary both because humans are born with brains that still have a long growth trajectory, and because it takes extra teaching investment to develop complex behaviours. Indeed, it may be argued that it was the combination of creativity, teaching, and learning that typifies childhood, which took us from being a cultural animal to being a cumulatively cultural one.
Kline's approach provides a new framework through which hitherto divided disciplines can find common ground for debating the phylogenetic and ontogenetic foundations of teaching, and promises to lead to new insights into one of the most critical of all social learning mechanisms. In it, she is right to ask why humans teach more than other animals. But the answer may be simpler than is outlined. It is because, unlike any other animal, we have children to teach.
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The Oldowan knapped stone industry appeared around 2.6 million years ago. Given a lack of evidence for trial and error in Oldowan knapping (De La Torre Reference De La Torre2004; Delagnes & Roche Reference Delagnes and Roche2005) some teaching may have underpinned the transmission of this technology. However, the technology and shape of Oldowan artefacts was largely controlled by the properties of the raw materials used, rather than by stylistic traditions (De La Torre Reference De La Torre2004; Toth Reference Toth1985). If teaching were to have occurred, it likely only needed to be what Kline defines as “lower-effort forms.” It is not until 1.75 million years ago, with the emergence of the Acheulean industry, that we see a shift in lithic construction hinting at the onset of Kline's “higher-effort forms of teaching.”
Acheulean technology involved the ability to strike large stone flakes and bifacially shape stone artefacts into hand-axes and cleavers (Beyene et al. Reference Beyene, Katoh, WoldeGabriel, Hart, Uto, Sudo, Kondo, Hyodoi, Renne, Suwa and Asfaw2013; Lepre et al. Reference Lepre, Roche, Kent, Harmand, Quinn, Brugal, Texier, Lenoble and Feibel2011). Consider cleaver manufacture from the 1.21 million year-old site of Isampur Quarry in South India (Shipton Reference Shipton2013). Cleavers are U-shaped bifaces with a broad bit as their principal cutting edge, manufactured by setting up platforms on thick slabs of limestone from which large flakes could be struck obliquely to the bedding plane, then retouched into the requisite shape (Petraglia et al. Reference Petraglia, LaPorta and Paddayya1999; Shipton et al. Reference Shipton, Petraglia and Paddayya2009). The manufacturing sequence involves several hierarchically organized stages, such as removing thick flakes from the slab perimeter to set up suitable platforms from which to strike the large blank flakes; and to a novice it would be unclear how some of these relate to the finished product (Shipton Reference Shipton2013). To understand why the platform is necessary requires sufficient experience to accurately identify the angles and surfaces that are good for striking large flakes. It is also important to note that Acheulean hand-axes and cleavers are deliberately shaped to be symmetrical, often in two planes (Wynn Reference Wynn2002), yet butchery experiments suggest that this symmetry may not greatly improve their utilitarian value (Machin et al. Reference Machin, Hosfield and Mithen2007). In other words, they feature unnecessary characteristics and were probably made using unnecessary processes. Demonstrating the requisite skills may have required one of Kline's higher forms of teaching in order to steer novice knappers to the same, somewhat arbitrary, outcomes.
But it is here that we are confronted with a conundrum that highlights a key aspect of the human condition missed by Kline. The Acheulean period stands out for its unparalleled homogeneity: The industry persists for around 1.5 million years (Shipton et al. Reference Shipton, Clarkson, Pal, Jones, Roberts, Harris, Gupta, Ditchfield and Petraglia2013). Compare this to a state-of-the-art personal computer purchased 10 years ago that is now so obsolete it is probably best employed as a piece of kitsch sculpture. Signs of cumulative culture in the Acheulean are, therefore, fleeting. What, then, is missing? The answer is hidden in Kline's target article. She is rightly at pains to point out that her examples of teaching are just that, and should not be taken as prescriptive. But note a key aspect of each example where humans are involved: All feature adult to child transmission, something that cannot occur if there are no children.
Due to the large size of our brain, but relatively narrow birth canal, humans are born in a state of altriciality where they depend on their parents for nourishment for longer than most animals (Bogin Reference Bogin and Panter-Brick1998). With the high metabolic demands of a brain that is still growing rapidly, humans have evolved “childhood,” a new life history stage in which older members of the social group provide specially prepared foods that are high in energy and nutrients for the young whose brains are growing rapidly, but whose bodies are growing slowly (Kaplan et al. Reference Kaplan, Hill, Lancaster and Hurtado2000; Locke & Bogin Reference Locke and Bogin2006). No other living species has this. Indeed, it may not have appeared until relatively late in our evolutionary history.
Reconstructions of extinct hominin life history using dental development, body mass, and brain growth point to a short or absent childhood in the earlier Acheulean hominin Homo erectus (for summaries, see Nielsen Reference Nielsen2012b; Robson & Wood Reference Robson and Wood2008). Childhood as we know it thus post-dates the emergence of Acheulian stone tools (Hopkinson et al. Reference Hopkinson, Nowell and White2013). In contrast, there is evidence of a childhood in Homo neanderthalensis (Smith et al. Reference Smith, Toussaint, Reid, Olejniczak and Hublin2007) who are, along with early Homo sapiens, associated with the establishment of Middle Paleolithic technology around 300,000 years ago. It is during the Middle Paleolithic that, under the right demographic circumstances, we begin to see instances of cumulative cultural evolution (d'Errico & Stringer Reference d'Errico and Stringer2011; Powell et al. Reference Powell, Shennan and Thomas2009). Notably, by the Late Acheulean period a handful of technological advances, such as the use of soft-hammers, had accrued (Stout et al. Reference Stout, Apel, Commander and Roberts2014), and there is evidence that the Late Acheulean hominin Homo heidelbergensis had childhood lengths more similar to our own than Homo erectus (Nowell & White Reference Nowell, White, Nowell and Davidson2012; Robson & Wood Reference Robson and Wood2008).
Childhood enables ample opportunity for play and discovery, and for entertaining the kinds of creativity that later in life undergird the imaginative endeavours that may bring new technological advances (Nielsen Reference Nielsen2012a; Reference Nielsen2012b). Childhood also affords multiple opportunities for extensive learning and for sophisticated cultural behaviors to arise (Bogin Reference Bogin1990) – and hence for more complex and detailed approaches to teaching. Childhood is necessary both because humans are born with brains that still have a long growth trajectory, and because it takes extra teaching investment to develop complex behaviours. Indeed, it may be argued that it was the combination of creativity, teaching, and learning that typifies childhood, which took us from being a cultural animal to being a cumulatively cultural one.
Kline's approach provides a new framework through which hitherto divided disciplines can find common ground for debating the phylogenetic and ontogenetic foundations of teaching, and promises to lead to new insights into one of the most critical of all social learning mechanisms. In it, she is right to ask why humans teach more than other animals. But the answer may be simpler than is outlined. It is because, unlike any other animal, we have children to teach.