- Email: [email protected]
Weird and wonderful artefacts
Update
TRENDS in Ecology and Evolution
least three reasons. First, it concerns long-term population censuses: 14 years for the sycamore aphid Drepanosiphum platanoidis, seven for the lime aphid Eucallipterus tiliae and 23 for the Turkey oak aphid Myzocallis boerneri. Although such long-term studies provide the ‘red meat’ of population ecology, they are rarely attempted, so it is especially useful to have a first-hand account from someone who has made a classic contribution to the field. Second, most insect–plant researchers work on leafchewers, whose activities are written on the vegetation, and often ignore the subtler effects of sapsuckers: a book where these take centre stage is, therefore, very welcome. Finally, Insect Herbivore–Host Dynamics has a surprisingly heterodox conclusion. The populations of these treedwelling sapsuckers is regulated neither by top-down control by natural enemies nor by bottom-up regulation by the plant, but by density-dependent mortality and migration within the aphid populations themselves. Dixon takes a robustly empirical approach throughout. Indeed, one detects a general disenchantment with the modern insistence on hypothesis-driven research. Facts are what matter to Dixon: census information ‘should not be seen mainly as a means of testing theory’, but as a means of providing an understanding of the system as a whole. In the two central chapters of the book, Dixon first establishes that there is no clear evidence that changes in either tree quality or in the abundance of natural enemies regulates the abundance of sycamore aphids. He then does a simulation analysis of within-year changes in abundance of the sycamore aphid and the Turkey oak aphid and generalizes this into a simple and convincing analytical model. This suggests that only two parameters (the effects of cumulative density and variations in carrying capacity) are required to explain the observed population cycles in
Vol.20 No.12 December 2005
655
these two species. Although this is convincing, a major concern, acknowledged by Dixon, is that these populations are in artificial, man-made habitats, and the whole picture might be different if the trees were part of a forest. In Insect Herbivore–Host Dynamics, Dixon discusses several other topics, such as sex allocation, where we are given another brief glimpse of the tantalizingly unavailable Seamus Ward ESS model, and the Hamilton and Brown autumnal coloration model, which Dixon refutes sensibly and interestingly. But the focus of his book is relentlessly narrow. Over 90% of the figures are from the author’s own work and much of the data is obtained from surveys of one species of aphid on eight trees in Glasgow. Tony Dixon, like Jane Austen it would seem, is content to restrict himself to working on a tiny bit of ivory. There is relatively little attempt to relate this work to that done on the aphids of herbaceous plants let alone to other insect herbivores. I think this is a pity. The book would have been much more useful, especially for students, if the author had used his great expertise on aphids to make connections with work done on other insect herbivores, including the well studied leaf chewers. But the sharp focus does have compensations. Insect Herbivore–Host Dynamics is short, uncluttered and digestible. It is totally free of the self-congratulatory anecdotage that can ensnare a scientist contemplating the upshot of his career. Its chief virtue is that you can quickly grasp the salient features of Dixon’s classic work on aphids without the chore of actually reading the original papers. But you will have to provide the context yourself. 0169-5347/$ - see front matter Q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.tree.2005.06.007
Weird and wonderful artefacts Animal Architecture by Michael Hansell. Oxford University Press, 2005. £60.00/£32.50 hbk/pbk (334 pages) ISBN 0 19 850751 8/0 19 850752 6
Gavin R. Hunt Department of Psychology, University of Auckland, Private Bag 92019, Auckland, New Zealand
Natural selection is responsible for an incredible range of weird and wonderful creatures, as well as much of their behaviour and what they make out of materials. We are often more taken by the artefacts of animals than by the animals themselves, perhaps because many artefacts seem downright clever. Hansell’s long-held enthusiasm for the subject comes across in this updated version of his 1984 book [1]. In an easily read scholarly Corresponding author: Hunt, G.R. ([email protected]). Available online 26 August 2005 www.sciencedirect.com
style intended for academics, he provides an up to date account of the scientific knowledge in the field. Hansell identifies three basic functions of artefacts made by animals: a home, prey capture and, less commonly, intraspecific communication. Examples are also provided of the unusual, rather than just artefacts such as beaver dams and caddis larval cases. The acoustic singing burrows of male mole crickets are only excavations and an elegant example of the simplicity of construction combined with the complexity of function. It becomes clear that complex artefacts such as the webs of orb spiders, large termite mounds and even the strange combined house– food trap of tadpole-like Oikopleura can be created with a ‘.simple nervous system making a series of simple
656
Update
TRENDS in Ecology and Evolution
decisions based on immediate rather than recalled information.’. After reading Animal Architecture, one should be convinced that most artefacts are what Richard Dawkins calls ‘extended phenotypes’ [2]. As adaptations, extended phenotypes generally evolve into complex and efficient designs over long periods of time, which Hansell explains can be subject to constraints of one sort or another. He provides ample examples of the challenges and rewards for researchers in determining not only the overall function of artefacts (this is not always obvious), but also the adaptive nature of the way in which they are made and the materials, if any, used. My main problem with Hansell’s generally excellent account is his confusion over tool manufacture (and use) (see also [3]). One would not guess from the title of the book (or the first chapter on ‘Functions’ for that matter) that tool manufacture was included, but this is explained by Hansell’s view that nonhuman tool manufacture belongs in a continuum with extended phenotypes (an anthropomorphic subdivision of tool manufacture if humans are excluded). If manufactured tools are invention-based implements, they do not belong in a continuum with extended phenotypes. Hansell, misguidedly in my view, finds little current evidence to suggest that tools manufactured by nonhumans are invention-based technology. The manipulative skills in nest building by weaver birds might be comparable to those in the manufacture of tools by New Caledonian crows, but the nests are probably extended phenotypes and manufactured tools are more likely to be invention-based technology. The different processes responsible for extended phenotypes and invention-based artefacts create technologies with distinctly different characteristics. Extended phenotypes are characterised by: (i) a long history of persistence in some form across species; (ii) within-species design variation that is closely associated with environmental variation; and (iii) lack of diversification within species; that is, one species makes one artefact. Based on the evolution of human technology, invention-based artefacts are characterised by: (i) a short history of persistence, if any, across species; (ii) within-species design variation that is not necessarily closely associated with environmental factors; and (iii) within-species design diversity. The tool technologies of New Caledonian crows and chimpanzees are more consistent with the characteristics of invention-based artefacts [4–6]. Hansell is surprised by the claims for complex cognition behind comparatively simple tools manufactured by nonhumans given that complex extended phenotypes can be produced by simple behaviour. However, he fails to explain
www.sciencedirect.com
Vol.20 No.12 December 2005
why manufactured tools are not only usually simple, but also extremely rare among animals. This contrasting simplicity and rarity should be expected if tool manufacture requires difficult-to-evolve cognitive capabilities. Also expected would be the correlation of cognitive capabilities with the complexity of invention-based technology (generally consistent for Galapagos finches, New Caledonian crows, chimpanzees and humans) but not with the complexity of extended phenotypes (compare the cognition of birds with that of termites). Further support for the idea that tool manufacture requires cognitive specialization is the association between tool behaviour and/or innovation propensity in mammals and birds and brain enlargement in areas responsible for intelligent behaviour [7,8]. The two living species with the most sophisticated tool manufacture, humans and New Caledonian crows, have highly encephalized brains and innovative and opportunistic foraging lifestyles. Animals such as crows might have a strong disposition to use, and sometimes make, tools without social learning [9], including in all likelihood humans, but this does not imply that manufactured tools are extended phenotypes. It is also revealing that innovative individuals of non-tool-using species can invent tool manufacture [10]. Hansell is right to be cautious, but there is considerable circumstantial evidence suggesting that manufactured tools are inventionbased technology. References 1 Hansell, M. (1984) Animal Architecture and Building Behaviour, Longman 2 Dawkins, R. (2004) Extended phenotype – but not too extended. A reply to Laland, Turner and Jablonka. Biol. Philos. 19, 377–396 3 McGrew, W.C. (1984) Beavering away. Nature 311, 183 4 Hunt, G.R. and Gray, R.D. (2003) Diversification and cumulative evolution in New Caledonian crow tool manufacture. Proc. R. Soc. London B Biol. Sci. 270, 867–874 5 Hunt, G.R. and Gray, R.D. (2004) The crafting of hook tools by wild New Caledonian crows. Proc. R. Soc. London B Biol. Sci. 271(Suppl.), S88–S90 6 McGrew, W.C. (1992) Chimpanzee Material Culture: Implications for Human Evolution, Cambridge University Press 7 Lefebvre, L. et al. (2002) Tools and brains in birds. Behaviour 139, 939–973 8 Reader, S.M. and Laland, K.N. (2002) Social intelligence, innovation, and enhanced brain size in primates. Proc. Natl. Acad. Sci. U. S. A. 99, 4436–4441 9 Kenward, B. et al. (2005) Tool manufacture by naı¨ve juvenile crows. Nature 433, 121 10 Jones, T.B. and Kamil, A.C. (1973) Tool-making and tool-using in the northern blue jay. Science 180, 1076–1078 0169-5347/$ - see front matter Q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.tree.2005.08.008
TRENDS in Ecology and Evolution
least three reasons. First, it concerns long-term population censuses: 14 years for the sycamore aphid Drepanosiphum platanoidis, seven for the lime aphid Eucallipterus tiliae and 23 for the Turkey oak aphid Myzocallis boerneri. Although such long-term studies provide the ‘red meat’ of population ecology, they are rarely attempted, so it is especially useful to have a first-hand account from someone who has made a classic contribution to the field. Second, most insect–plant researchers work on leafchewers, whose activities are written on the vegetation, and often ignore the subtler effects of sapsuckers: a book where these take centre stage is, therefore, very welcome. Finally, Insect Herbivore–Host Dynamics has a surprisingly heterodox conclusion. The populations of these treedwelling sapsuckers is regulated neither by top-down control by natural enemies nor by bottom-up regulation by the plant, but by density-dependent mortality and migration within the aphid populations themselves. Dixon takes a robustly empirical approach throughout. Indeed, one detects a general disenchantment with the modern insistence on hypothesis-driven research. Facts are what matter to Dixon: census information ‘should not be seen mainly as a means of testing theory’, but as a means of providing an understanding of the system as a whole. In the two central chapters of the book, Dixon first establishes that there is no clear evidence that changes in either tree quality or in the abundance of natural enemies regulates the abundance of sycamore aphids. He then does a simulation analysis of within-year changes in abundance of the sycamore aphid and the Turkey oak aphid and generalizes this into a simple and convincing analytical model. This suggests that only two parameters (the effects of cumulative density and variations in carrying capacity) are required to explain the observed population cycles in
Vol.20 No.12 December 2005
655
these two species. Although this is convincing, a major concern, acknowledged by Dixon, is that these populations are in artificial, man-made habitats, and the whole picture might be different if the trees were part of a forest. In Insect Herbivore–Host Dynamics, Dixon discusses several other topics, such as sex allocation, where we are given another brief glimpse of the tantalizingly unavailable Seamus Ward ESS model, and the Hamilton and Brown autumnal coloration model, which Dixon refutes sensibly and interestingly. But the focus of his book is relentlessly narrow. Over 90% of the figures are from the author’s own work and much of the data is obtained from surveys of one species of aphid on eight trees in Glasgow. Tony Dixon, like Jane Austen it would seem, is content to restrict himself to working on a tiny bit of ivory. There is relatively little attempt to relate this work to that done on the aphids of herbaceous plants let alone to other insect herbivores. I think this is a pity. The book would have been much more useful, especially for students, if the author had used his great expertise on aphids to make connections with work done on other insect herbivores, including the well studied leaf chewers. But the sharp focus does have compensations. Insect Herbivore–Host Dynamics is short, uncluttered and digestible. It is totally free of the self-congratulatory anecdotage that can ensnare a scientist contemplating the upshot of his career. Its chief virtue is that you can quickly grasp the salient features of Dixon’s classic work on aphids without the chore of actually reading the original papers. But you will have to provide the context yourself. 0169-5347/$ - see front matter Q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.tree.2005.06.007
Weird and wonderful artefacts Animal Architecture by Michael Hansell. Oxford University Press, 2005. £60.00/£32.50 hbk/pbk (334 pages) ISBN 0 19 850751 8/0 19 850752 6
Gavin R. Hunt Department of Psychology, University of Auckland, Private Bag 92019, Auckland, New Zealand
Natural selection is responsible for an incredible range of weird and wonderful creatures, as well as much of their behaviour and what they make out of materials. We are often more taken by the artefacts of animals than by the animals themselves, perhaps because many artefacts seem downright clever. Hansell’s long-held enthusiasm for the subject comes across in this updated version of his 1984 book [1]. In an easily read scholarly Corresponding author: Hunt, G.R. ([email protected]). Available online 26 August 2005 www.sciencedirect.com
style intended for academics, he provides an up to date account of the scientific knowledge in the field. Hansell identifies three basic functions of artefacts made by animals: a home, prey capture and, less commonly, intraspecific communication. Examples are also provided of the unusual, rather than just artefacts such as beaver dams and caddis larval cases. The acoustic singing burrows of male mole crickets are only excavations and an elegant example of the simplicity of construction combined with the complexity of function. It becomes clear that complex artefacts such as the webs of orb spiders, large termite mounds and even the strange combined house– food trap of tadpole-like Oikopleura can be created with a ‘.simple nervous system making a series of simple
656
Update
TRENDS in Ecology and Evolution
decisions based on immediate rather than recalled information.’. After reading Animal Architecture, one should be convinced that most artefacts are what Richard Dawkins calls ‘extended phenotypes’ [2]. As adaptations, extended phenotypes generally evolve into complex and efficient designs over long periods of time, which Hansell explains can be subject to constraints of one sort or another. He provides ample examples of the challenges and rewards for researchers in determining not only the overall function of artefacts (this is not always obvious), but also the adaptive nature of the way in which they are made and the materials, if any, used. My main problem with Hansell’s generally excellent account is his confusion over tool manufacture (and use) (see also [3]). One would not guess from the title of the book (or the first chapter on ‘Functions’ for that matter) that tool manufacture was included, but this is explained by Hansell’s view that nonhuman tool manufacture belongs in a continuum with extended phenotypes (an anthropomorphic subdivision of tool manufacture if humans are excluded). If manufactured tools are invention-based implements, they do not belong in a continuum with extended phenotypes. Hansell, misguidedly in my view, finds little current evidence to suggest that tools manufactured by nonhumans are invention-based technology. The manipulative skills in nest building by weaver birds might be comparable to those in the manufacture of tools by New Caledonian crows, but the nests are probably extended phenotypes and manufactured tools are more likely to be invention-based technology. The different processes responsible for extended phenotypes and invention-based artefacts create technologies with distinctly different characteristics. Extended phenotypes are characterised by: (i) a long history of persistence in some form across species; (ii) within-species design variation that is closely associated with environmental variation; and (iii) lack of diversification within species; that is, one species makes one artefact. Based on the evolution of human technology, invention-based artefacts are characterised by: (i) a short history of persistence, if any, across species; (ii) within-species design variation that is not necessarily closely associated with environmental factors; and (iii) within-species design diversity. The tool technologies of New Caledonian crows and chimpanzees are more consistent with the characteristics of invention-based artefacts [4–6]. Hansell is surprised by the claims for complex cognition behind comparatively simple tools manufactured by nonhumans given that complex extended phenotypes can be produced by simple behaviour. However, he fails to explain
www.sciencedirect.com
Vol.20 No.12 December 2005
why manufactured tools are not only usually simple, but also extremely rare among animals. This contrasting simplicity and rarity should be expected if tool manufacture requires difficult-to-evolve cognitive capabilities. Also expected would be the correlation of cognitive capabilities with the complexity of invention-based technology (generally consistent for Galapagos finches, New Caledonian crows, chimpanzees and humans) but not with the complexity of extended phenotypes (compare the cognition of birds with that of termites). Further support for the idea that tool manufacture requires cognitive specialization is the association between tool behaviour and/or innovation propensity in mammals and birds and brain enlargement in areas responsible for intelligent behaviour [7,8]. The two living species with the most sophisticated tool manufacture, humans and New Caledonian crows, have highly encephalized brains and innovative and opportunistic foraging lifestyles. Animals such as crows might have a strong disposition to use, and sometimes make, tools without social learning [9], including in all likelihood humans, but this does not imply that manufactured tools are extended phenotypes. It is also revealing that innovative individuals of non-tool-using species can invent tool manufacture [10]. Hansell is right to be cautious, but there is considerable circumstantial evidence suggesting that manufactured tools are inventionbased technology. References 1 Hansell, M. (1984) Animal Architecture and Building Behaviour, Longman 2 Dawkins, R. (2004) Extended phenotype – but not too extended. A reply to Laland, Turner and Jablonka. Biol. Philos. 19, 377–396 3 McGrew, W.C. (1984) Beavering away. Nature 311, 183 4 Hunt, G.R. and Gray, R.D. (2003) Diversification and cumulative evolution in New Caledonian crow tool manufacture. Proc. R. Soc. London B Biol. Sci. 270, 867–874 5 Hunt, G.R. and Gray, R.D. (2004) The crafting of hook tools by wild New Caledonian crows. Proc. R. Soc. London B Biol. Sci. 271(Suppl.), S88–S90 6 McGrew, W.C. (1992) Chimpanzee Material Culture: Implications for Human Evolution, Cambridge University Press 7 Lefebvre, L. et al. (2002) Tools and brains in birds. Behaviour 139, 939–973 8 Reader, S.M. and Laland, K.N. (2002) Social intelligence, innovation, and enhanced brain size in primates. Proc. Natl. Acad. Sci. U. S. A. 99, 4436–4441 9 Kenward, B. et al. (2005) Tool manufacture by naı¨ve juvenile crows. Nature 433, 121 10 Jones, T.B. and Kamil, A.C. (1973) Tool-making and tool-using in the northern blue jay. Science 180, 1076–1078 0169-5347/$ - see front matter Q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.tree.2005.08.008