Conflicting Evolutionary Pressures on Human Cognition: A Case Study of Autism Callum Scott MA by Research University of York Archaeology December 2017 2 Abstract The current dominant view is that the evolutionary pressures leading to our large brain sizes were predominantly social. This study investigates the effects of both technical and social pressures on our cognitive evolution, to determine whether the pressures were more complex than social theories allow. This is assessed both between hominin species and within our species. Between species effects are determined by evaluating the evolution of human cognition in 4 stages. Archaeological evidence of behaviour and changes in brain structure are presented for each stage. This allows specializations to be identified, and permits us to suggest whether specialization in each species was in response to social pressures, or a more complex pattern of both technical and social pressures. The results of this evaluation support a more complex pattern of evolutionary pressures. Within species effects are assessed, using Autism Spectrum Condition (ASC) as an example of an alternate, more technically focused, adaptive strategy. This condition accentuates technical behavioural traits which would be advantageous to a Palaeolithic population. The genetics of the condition show that it is highly heritable, was likely present prior to 200ka, and under positive selection. Thus, these technical traits must have had an impact on past populations. A survey is conducted to assess whether characteristics and components of autism would influence individual’s engagement with material culture, in particular art. It found that the technical trait, high attention to detail, was associated with experience of art and susceptibility to pareidolic illusions. Previously it has been suggested that illusions such as this may be implicated in the origins of art. This provides an example of how individuals with enhanced technical traits within our species may have affected our cultural evolution. Thus, the role of technical pressures in our evolution and how they relate to social pressures requires more attention. 3 Contents Abstract ........................................................................................................................ 2 Acknowledgments ......................................................................................................... 7 Author’s Declaration ..................................................................................................... 7 Chapter 1: Introduction ................................................................................................. 8 1.1 Context and Significance ..................................................................................... 8 1.2 Aims .................................................................................................................... 9 1.3 Objectives ......................................................................................................... 11 Chapter 2: An Introduction to Evolutionary Pressures ................................................. 12 2.1 Defining Evolutionary Pressures On Cognition .................................................. 12 2.2 Social Cognition, the Dominant Narrative .......................................................... 13 Chapter 3: An Evaluation of Conflicting Evolutionary Pressures Between Species ..... 19 3.1 Primates ............................................................................................................ 19 3.2 Early Homo ....................................................................................................... 23 Archaeological Evidence of Behaviour ................................................................. 23 Changes in Brain Structure .................................................................................. 25 3.3 Homo erectus and Homo heidelbergensis ......................................................... 26 Archaeological Evidence of Behaviour ................................................................. 26 Changes in Brain Structure .................................................................................. 31 3.4 Neanderthals and Humans ................................................................................ 37 Archaeological Evidence of Behaviour ................................................................. 37 Changes in Brain Structure .................................................................................. 42 3.5 Conclusion ........................................................................................................ 44 Chapter 4: An Evaluation of Conflicting Evolutionary Pressures Within Species: A Case Study of Autism Spectrum Condition ........................................................................... 46 4.1 Behaviour .......................................................................................................... 46 Theory of Mind ..................................................................................................... 46 Weak Central Coherence ..................................................................................... 48 Executive Functions ............................................................................................. 50 Archaeological Interpretations ............................................................................. 51 4.2 Neurology .......................................................................................................... 53 4.3 Genetics ............................................................................................................ 57 Heritability ............................................................................................................ 57 Genetic Causes ................................................................................................... 58 4.4 Conclusions ....................................................................................................... 61 4 Chapter 5: Detail Focus - An Archaeological Application ............................................ 62 5.1 Introduction ....................................................................................................... 62 5.2 Methods ............................................................................................................ 63 5.3 Results .............................................................................................................. 64 AQ Test ............................................................................................................... 64 Correct Identification Scores ................................................................................ 70 Imagined Figure Scores ....................................................................................... 70 5.4 Discussion ......................................................................................................... 76 5.5 Limitations ......................................................................................................... 82 5.6 Conclusions ....................................................................................................... 84 Chapter 6: Summary and Final Conclusions ............................................................... 86 Appendix .................................................................................................................... 88 Appendix A – The Visual Cognition and Perception Survey .................................... 88 Appendix B – Tables of Correct Identification Scores for individual categories of the AQ test. ................................................................................................................. 107 Appendix C – Tables of Imagined Figure Scores for individual categories of the AQ test. ....................................................................................................................... 109 Figures Figure 1. Chart of the dissertation’s structure .............................................................. 10 Figure 2. Hominin brain size plotted against time with orders of intentionality in numerals inside boxes (McNabb 2012). ...................................................................... 16 Figure 3. Hominin female body weight as a percentage of male body weight, higher percentage suggests less dimorphism (data from Leonard & Robertson 1994; Leonard et al. 2003; McHenry & Coffing 2000; Sorensen & Leonard 2001). ............................. 31 Figure 4. (A) Hominin average body weight (kg) separated by male and female. (B) Average Hominin Brain size (g). (data from Ben-Dor et al. 2011; Leonard & Robertson 1994; Leonard et al. 2003; McHenry & Coffing 2000; Sorensen & Leonard 2001). ..... 32 Figure 5. Estimated variations in temperature during the last glacial cycle using oxygen isotope and deuterium ratios from the Voztok ice core, with oxygen isotope phases marked (After Jouzel et al. 1987). ............................................................................... 37 Figure 6. Example of an Embedded Figure, where the image of the ‘hidden house’ must be found within the horse. .................................................................................. 50 Figure 7. An example of a block design test, where the blocks on the right must be arranged to produce the image on the left................................................................... 50 Figure 8. Comparison of horses by