Evolution of Empathizing and Systemizing personality traits - a draft book chapter, request for comments

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The following is a draft book chapter I co-wrote for a book on Systemizing and Empathizing which was to be edited by the originator of these terms - Simon Baron-Cohen.

 

In the draft, Patrick Rosenkranz and I put forward some new hypotheses for the evolution of these personality traits - and these may be of some general interest.

 

However, the original contract for this book fell-through, and a new publisher is being arranged. This means that there will be time, and need, for the draft chapter to be revised considerably before publication.

 

Therefore, if anyone has suggestions and comments for how this book chapter might be improved these would be gratefully received.

 

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Evolution of Empathizing and Systemizing:  Economic specialization and the sexual division of labour

 

By Patrick Rosenkranz and Bruce G Charlton

 

 

Draft version February 2013: , Psychology

 

Email: brucedotcharltonatncldotacdotuk

 

 

Introduction: What is it that needs to be explained?

 

The first purpose of this chapter is conceptual clarification. In other words, we first aim to clarify what an evolutionary theory of Empathizing and Systemizing needs to explain. In other words, we need to be clear what has evolved, before we can suggest why and how it may have evolved.

 

Therefore we need to define the nature of both Empathizing (E) and Systemizing (S), and to emphasize that they are personality traits rather than abilities. We consider E as the disposition to apply ‘theory of mind’ (or social intelligence) reasoning to experience; while Systemizing is a disposition to apply non-social, abstract and systematic reasoning to experience. Therefore, E and S are distinctive modes of thinking – in an identical situation, an Empathizer would use one mode of thinking, while a Systemizer would use another – even if both had the same underlying cognitive abilities, their preferences or dispositions would be different.

 

To put matters simply, E and S describe a fundamental orientation towards either People or Things. An orientation could be understood in terms of a spontaneous focus, a preference. The reason for an orientation may be sought in terms of motivational systems of gratification and aversion: a concern with either people, or things, will tend to give more pleasure (or less pain) than its opposite.

 

But the situation is not symmetrical for Empathizing and Systemizing, because man is a social animal: thus a focus on people is to be expected, while a focus on things in preference to people is unexpected, and invites specific explanation.

 

In evolutionary terms, we need to explain how it was possible that a preference to deal with things rather than people was able to arise, specifically in men more strongly than in women (Baron-Cohen, 2003)– in face of our presumption that a preference for things over people would be likely to provide a selective disadvantage in terms of social relationships. In particular, this would probably be a disadvantage from the perspective of sexual selection in its major form of female sexual choice.

 

In a nutshell: we need to explain why ancestral women could have ended-up with a mate who was more interested in things than they were interested in other people (such as herself). 

 

The second (and main) purpose of this chapter is to describe specific hypotheses as to how and why E and S traits may have evolved in ancestral humans, what may have been their pay-offs in terms of reproductive success under specific conditions, and to clarify the reason for the reciprocity of these traits and the existence of sex differences(Baron-Cohen, 2003).

In brief we regard Empathizing as the default human personality since, as the application of social intelligence,  it reflects the great importance of social relationships to reproductive success. By contrast, we regard Systemizing as having emerged later in evolutionary history as a result of novel selection pressures due to changed economic conditions - especially the development of more-complex humans societies (such as agriculture and trade) with a variety of socially- essential, specialized jobs for men. 

 

These evolutionary hypotheses are, at this point, necessarily speculative and intended to serve as a guide for future empirical research rather than to provide definitive answers.

 

Empathizing and Systemizing conceptualized as personality traits

 

Empathizing and Systemizing are conceptualized as personality traits, dispositions or preferences to behave in certain ways; therefore not as cognitive abilities. E-S variations are this not-necessarily correlated with cognitive abilities – and indeed in some studies there is no significant measurable correlation with cognitive abilities. For example, there is neither a strong nor consistent association between the ‘reading the mind in the eyes’ test (a test of a cognitive ability), and scores on a self-evaluation Empathizing scale (a measure of disposition or personality): so that an individual may score highly at reading the mind in the eyes but score low on an Empathizing scale, or vice versa (Lawrence, Shaw, Baker, Baron-Cohen, & David, 2004; Voracek & Dressler, 2006).

 

A disposition is a personality trait: understandable as a sustained tendency, an individual’s characteristic of habitually deploying a mode of cognition. A disposition can also be seen as an individual’s preference for using an ability. (In the sense that preferences can only select between a certain set of abilities; one cannot characteristically be disposed to act in any way that one is incapable of acting.).

 

And preference to behave in certain ways is (presumably) based on a motivation, and motivation is associated with a psychological reward (or gratification) from doing something – or else a psychological punishment (or aversive consequence) of not doing something.

 

Ultimately, therefore, a disposition reflects that certain types of behaviour lead to increased gratification (increased pleasure or diminution of suffering). Individuals differ in the types of behaviour which lead to gratification, and in the degree of gratification associated with a specific type of behaviour.

 

In sum, individual and groups variations in Systemizing and Empathizing can be understood as variations in the type of behaviour that (on average) lead to gratification. Put simply, Empathizers gain enhanced gratification from Empathizing behaviour, while Systemizers gain enhanced gratification from Systemizing behaviour. For example, a High-Systemizer may have the ability to understand and empathize with other people, but prefers to spend most of his time doing crosswords; while a High-Empathizer may be able to do crosswords to a high standard, but she would prefer to converse with a group of friends. 

 

Naturally, the disposition to be Empathizing or Systemizing requires that there be the cognitive ability to do these; to empathize requires the ability to empathize and to systemize requires that ability. And at extremes of disposition there may be a deficit in such abilities, so that the extreme Empathizer may be defective in systematizing ability and the extreme Systemizer may be defective in theory of mind ability.

 

However, deficiencies in either E or S ability are not necessary to the finding of variations in E-S, and it seems that there may be a wide range of E-S dispositions even when both abilities are fully intact. Therefore, these abilities must have evolved in order that there be a disposition to use them.

 

Evolution of the Social Brain

 

The social brain hypothesis sees social selection pressures as the driving force behind human brain growth: higher cortical functions have evolved to deal with the adaptive problems of complex group living{Dunbar, 1995 #47} {Dunbar, 1995 #47}{Dunbar, 1995 #47}{Dunbar, 1998 #48}{Adolphs, 1999 #1}{Humphrey, 1976 #74}{Dunbar, 1995 #47}{Dunbar, 1998 #48}(Adolphs, 1999, 2009; Dunbar, 1995, 1998; Humphrey, 1976). The relative neo – cortex growth in humans and other primates is due to the demands on executive brain function required by living in complex social groups. Evidence in favour of this hypothesis shows that as group size increases across primate species, neo-cortex size also grows(Dunbar, 1995, 1998) {Dunbar, 1995 #47}{Dunbar, 1998 #48}. The set of cognitive adaptations that enables successful group living such as the abilities to perceive, recall and process information about others and act according to this information, is often termed social intelligence (Dunbar, 1998), Machiavellian intelligence (Byrne & Whiten, 1988) or social cognition (Brothers, 1990).    

Group living poses a number of adaptive problems for the individual: attracting and maintaining a mate, monitoring and manipulating social interactions, outwitting rivals and forming alliances, inferring dispositions, motivations and intentions of others, etc . Selection favoured those individuals who were the most successful at solving these adaptive problems of group living. In order to successfully survive and reproduce within a social setting, an individual requires the cognitive ability to react adaptively to social challenges and to affect others positively(Byrne & Whiten, 1988){Byrne, 1988 #122} {Byrne, 1988 #122}.

 

Amongst the cognitive abilities enabling complex social interaction are face perception, emotional processing, theory of mind (TOM), self-reference and working memory (Grady & Keightley, 2002). These abilities are mediated by interplay of activity of networks of interdependent brain regions which support the behaviours necessary for social interaction (Grady& Keightley, 2002). Amongst the neural architecture that contributes to social intelligence are the amygdala ventromedial prefrontal cortex and the right somatosensory related cortex (Adolphs, 1999; Grady & Keightley, 2002).

 

An individual clearly benefits in terms of reproductive success by being able to predict the behaviour of others within the group, maintain beneficial social relationships and even manipulating social situations to her own advantage(Byrne& Whiten, 1988; Humphrey, 1976). A lack of the faculties required to function adaptively within the group can have negative reproductive consequences for the individual. The inability to positively affect others, at least to a degree, and to adaptively interact within a group can lead to negative emotional effects for the individual, social ostracism and ultimately, reproductive death .This can most clearly be seen in the devastating effects of lesions and or disorders to the social functioning of the individual(Ylvisaker, Feeney, & Szekeres, 1998). For instance, individuals with the autistic spectrum disorder have abnormal face perception (Klin et al., 1999) as well as strong deficits in the theory of mind mechanism (Grady& Keightley, 2002). Autistic individuals have difficulties in adaptive social behaviour, avoid normal social contact and are generally indifferent to social encounters (Baron-Cohen, 1997).

 

At the core of social intelligence lies the ability to “mind read” or theory of mind: this is the ability to infer  the contents (beliefs, desires, intentions) of the mind of other individuals, predicting behaviour based on these inferences and empathizing with others states of mind (Baron-Cohen, 1999, 2000, 2006b; Baron-Cohen, Leslie,& Frith, 1985; Dennett, 1971; Premack & Woodruff, 1978). Mindreading is often seen as a predominantly cognitive ability, however emotions play a key role in inferring other agent’s content of mind and reactive adaptively.

 

 

Emotions and the somatic marker mechanism

 

Empathizing has evolved to represent the affective states of others and to react with an appropriate emotion. The importance of emotions in adaptive social behaviour is extensive; and they are pivotal in successfully modelling social behaviour. Relevant here is the somatic marker mechanism suggested by Antonio Damasio (Damasio, 1994, 1996, 1999) and further elaborated upon by Charlton (Charlton, 2000, 2003; Charlton & McClelland, 1999).

 

At the outset, Damasio (Damasio, 1994, 1995, 1999) makes a distinction between emotions and feelings: Emotions are changes in body state (and non-conscious brain state to a secondary extent) primed by either external or internal stimuli. Feelings are the conscious awareness of these changes in body state (Damasio, 1994, 1995). Primary emotions are those that are innate and triggered automatically in certain situations (Charlton, 2000, 2003; Damasio, 1995).  For instance, a “fear” response can be triggered in the presence of a snake. The somatic response in this case would be an increase in heart rate, higher frequency of breathing, dilated pupils etc. This pattern of somatic changes constitutes the emotion of fear which can prime and initiate behaviour, such as a flight or fight response. These changes in body states can be observed in most mammals, however, it’s probably only primates and certainly humans that can be aware of emotions – that is, experience feelings (Charlton, 2000)

Secondary emotions are those emotions triggered by internal events such as remembering an encounter with a snake. Secondary emotions are induced by cognitive representations, i.e. internal events that have previously been associated with a primary emotion. These representations are dispositional in that they include evaluative information about the object/event priming the emotion in the first place. Thus, remembering an encounter with a snake can invoke the same changes in body state as the initial encounter. Secondary emotions can therefore be seen as being acquired through experience and are built upon the foundations of primary emotions (Damasio, 1995). In a nutshell, secondary emotions occur in response to cognitive modelling or cognitive simulations – such as memories or plans (Charlton, 2000).

 

Feeling an emotion is the conscious awareness of this pattern of changes in body state in relation to the representation that primed these changes. Thus, representations are juxtaposed with relevant somatic states, i.e. emotions, to the extent that these representations are associated or marked with a particular emotion. This juxtaposition of representation and emotion is what constitutes the somatic marker mechanism (Charlton, 2000; Damasio, 1994).

According to Damasio (Damasio, 1994, 1996) the somatic marker mechanism is fundamental to human reasoning and decision making especially within the social and personal realm. The neurobiological site which is critical for the somatic marker mechanism to function is the prefrontal cortex, more specifically the ventro-medial sector (Damasio, 1996). Individuals with damage to this section of the cortex have strong difficulties making appropriate social decisions, while still retaining most intellectual capacities (Damasio, 1996).

 

Ultimately, a good decision for any organism is one that is advantageous for the reproductive success and survival of the organism, as well as the quality of survival (Damasio, 1994, p. 169). Somatic markers assist and guide the decision making process by modelling outcomes of decisions through changes in somatic state. A possible bad outcome of a decision can manifest itself as an immediate negative feeling such as fears, misery or disgust. The representation of the negative outcome of a given response option is marked with the unpleasant feeling, allowing the organism to reject a possible decision from the outset. Thus, in Damasio’s words “somatic markers are special instances of feelings, generated from secondary emotions. Those emotions and feelings have been connected, by learning, to predicted future outcomes of certain scenarios.” (Damasio, 1994, p. 174). The somatic marker mechanism functions as both a warning and incentive system for possible negative and positive outcomes.

 

When somatic markers operate consciously, they can assist in the modelling and planning of behaviour towards other organisms. By thinking about previous social encounters and being aware of the emotional /somatic responses that are evoked through these deliberations, dispositions and intentions of others can be inferred (Charlton, 2000; Damasio, 1994) .This means that somatic markers are pivotal in internally modelling social behaviour.

Representations of others are linked in working memory with an appropriate feeling, thus associating own emotional reactions with the representation of others. For instance, the perception of a rival male can invoke the emotional reaction of fear.  The perceptual representation of this individual is then marked with the somatic state of fear. At a later point in time, thinking about this individual, i.e. drawing upon the representation from long term memory can similarly produce the same emotional reaction. Inferences about the disposition of the other individual can be modelled upon the own emotional reaction to the encounter (Charlton, 2000).

 

The somatic marker mechanism can be seen as being the underlying neurobiological mechanism of the theory of mind mechanism and the empathizing system .Where Baron-Cohen (2005) describes the development and function of these two systems, Damasio’s somatic marker explain the underlying neurobiological mechanism by which both dispositions and inferences about another organisms’ mental as well as affective  states can be made.

 

Because human intelligence and consciousness have fundamentally evolved to deal with the social world, the spontaneous and immediate experience of the environment is infused by social information. Humans are primed to interpret ambiguous situation (like the fluttering of leaves) as being caused by agency (Barrett, 2000; Guthrie, 1995) and to reading social meaning into natural events  (Bering, 2002). This tendency to anthropomorphise the significant environment and to imbue it with social agency may underlie the evolution of religious beliefs (Charlton, 2002a, 2002b; Guthrie, 1995; Rosenkranz & Charlton, in press).

 

Empathizing evolved to focus on people, Systemizing to focus on things

Evolved function of Empathizing – social focus

 

Empathizing is based upon the ‘theory of mind’ ability. Theory of mind refers to the ability, found in some social animals, to infer metal contents such as dispositions, motivations and intentions in another con-specific.

 

We conceptualize Empathizing as the disposition to apply ‘theory of mind’ cognitive ability – this can be applied to the social situations for which the ability (presumably) evolved, and also to understanding the world in general (and not just the social world). In other words, Empathizing is the spontaneous tendency to focus on people.

 

Since humans are social animals, and in line with evolutionary concepts such as the Social Brain and ‘Machiavellian Intelligence’, we regard social intelligence as probably deriving from primate ancestry, and closer to the spontaneous form of human interest than is an interest in things. We therefore regard the highly Empathizing personality type as underpinned by an evolutionarily more-ancient personality type than is Systemizing.

In other words, Empathizing is more fundamental to humans than Systemizing and intrinsic to the species: Empathizing came before Systemizing. Further, it is possible that a preference for Systemizing did not evolve in all populations, and may be weak or absent in some human groups still extant. But in ancestral hunter gatherer situations – perhaps including pre-modern hominid ancestors – we would assume that all reproductively successful humans were not just able to infer theory of mind, but disposed to focus on other humans and their mental contents: almost everybody in these circumstances was probably a high Empathizer and it is likely that the the Systemizing trait was low, and that there may have been few or zero high Systemizers.

 

Empathizing – in its evolutionary origins - is therefore personal in its application, being specifically directed towards actual human relationships. To have an Empathizing disposition is use this cognitive style (evolved to deal with humans) as a general model of understanding. Therefore be a high Empathizer is to see the world through social spectacles: a tendency to focus attention on social relationships and to understand the world as analogous to social relationships.

 

Empathizing seems to be the natural and spontaneous way for humans to deal-with phenomena they regard as important: this is seen in the tendency to anthropomorphise large and important animals, significant places and landscape features, treasured possessions and so on; and to treat human groups (or modern institutions) as if they were unified, conscious and intentional organisms.

 

Re-defining Systemizing as a preference for focusing on linear sequences of things

 

The usual definition of the trait of Systemizing relates to a preference to analyze the world in terms of the rules which govern systems: such that the Systemizer is a person who sees the world as composed of systems, and is interested in categorization and understanding the rules, patterns or principles that underlie these systems(Baron-Cohen, 2010; Baron-Cohen, Ashwin, Ashwin, Tavassoli,& Chakrabarti, 2009).

 

However, while this is an accurate description of the interests of a high Systemizing personality who also has high general intelligence, it is a potentially misleading description of the Systemizing trait since it refers to the understanding of complex systems, that is systems of processes that are governed by rules.

 

Yet it seems plausible that an interest in the abstract understanding of the processes of complex systems is underpinned (and evolutionarily preceded) by the simpler abstract task of learning linear sequences. So in terms of a personality trait, the interest in complex systems which is measured by Systemizing questionnaires may be considered a more advanced type of an elementary interest in simpler ‘strings’ of facts, names, numbers, tasks or procedures.

 

To create categorizations, to infer a pattern, and to extract the rules from a system are in fact higher-level cognitive abilities; possible only to those of relatively high general intelligence. Abstraction of rules is, indeed, one of the main attributes of ‘g’ which is measured in standard IQ tests: for example in supplying the next member of a number series, or establishing group membership, or performing a task like Raven’s matrices (Deary, 2001; Gottfredson, 2005; Jensen, 1998).Those of low general intelligence are poor at these tasks (which is why they are used to measure IQ), and this implies that a focus on understanding the rules of systems is a high-level definition of Systemizing.

 

Therefore, while inferring categories, patterns and rules certainly count as Systemizing, we would favour a more basic and less cognitively-advanced basis for defining systematizing: that the Systemizing trait is seen at its most basic in trying to learn linear sequences of abstract facts or actions.

 

The two main aspects of Systemizing, we suggest, relate to the nature of content which is not-social i.e. abstract; and to the content being understood in terms of linear sequences of facts. Therefore Systemizing relates to:

 

→     Abstract phenomena (things not people)

→     Of a specific identity (these particular things)

→     In a specific order (in this order, or categorized thus)

 

A modern example of the Systemizing preference, would be the kind of crazes and ‘obsessions’ which are characteristic of people on the autism spectrum or with Asperger’s syndrome: learning lists of names and numbers from the telephone directory, or certain types of dates, or pictures make by highly-literal copying, or learning all the facts on a non-social themes such as automobile performance or the performance of a sports team, or literal recollection of sequences from favourite TV shows or passages from books, or hobbies involving collecting and arranging – such as stamps, cards or train-spotting.

 

These and other pastimes such as crossword or other puzzles, or some types of computer games, are often about assembling sequences of correct facts or procedures (united by theme or category) in a correct and specific order or pattern – yet these facts or procedures may not have any rule-based ‘systemic’ structure. Typically, one cannot learn these kinds of activity by learning and applying rules; rather, the activity consists in performing exact sequences of correct responses on specific material.

 

Interestingly, an explanation of Systemizing in terms of the disposition to focus upon ‘close-up’ consideration of abstract linear sequences, bears striking similarities with the concept of left cerebral hemisphere dominance as described in Iain McGilchrist’s The master and his emissary concerning autistic traits and ‘attention to detail’ (Baron-Cohen et al., 2011; McGilchrist, 2009); although at the same time McGilchrist’s evidence and argument renders implausible any direct equation of left hemisphere with male, right with female. The argument is complex and we flag it here as a matter deserving further and detailed consideration.

 

Systemizing and psychological neoteny

 

Indeed, this kind of behaviour focused on linear sequence of abstract knowledge is characteristic of children; for instance when they insist on a fairy story being told with exactly the same words and details. Many pre-adolescent boys, in particular, have periodic ‘crazes’ on various subjects (aircraft, trains, a type of book, a type of construction model, a particular sport) about which theme they voraciously learn everything they can manage.

 

These pre-adolescent boy’s crazes are typically not focused on people nor on social relations, nor are they focused on rule-based understanding; rather they are fact-based, convergent activities involving listing, collecting, categorizing, memorizing – based on learning sequences and patterns but not often complex or dynamic ‘systems’.

 

This similarity between pre-adolescent boys and high Systemizing men does not tell us why high trait Systemizing may have evolved – does not tell us how high Systemizing may have improved differential reproductive success in our ancestors - but it may suggest how high Systemizing evolved: by perpetuation of pre-adult behaviour into sexual maturity. In other words high Systemizing trait in adults may be a neotenous phenomenon.

 

(Neoteny is one type of the more general class of ‘heterochrony’in which evolutionary change is brought about by alterations in the timing of developmental events (Horder, 2001)

 

And this may provide a clue to the proximate mechanism for the evolution of higher levels of trait Systemizing. Natural selection usually works by quantitative modification or amplification of some already-existing trait (as when a hand, or an arm, evolves into a wing in a bat, or a bird; or when a neck, or a nose, become lengthened in a giraffe, or an elephant). In humans, the evolution of the high levels of Systemizing seen in modern people suggests that there was some original trait which underwent evolutionary adaptation.

 

In other words; if neoteny – or something similar – was the proximate mechanism via which natural selection led to Systemizing, then we need to consider the trait which was present in immature humans that may have provided the basis for the evolution of adult Systemizing.  

 

E-S reciprocity and sex differentials generated by selection pressure from economic factors

 

What are the main observations concerning E and S which an evolutionary hypothesis must explain? One is the reciprocity between Empathizing and Systemizing – that when one is high the other is usually low.

 

In a sense, reciprocity is an intrinsic property of some personality traits: one cannot be both highly extravert and highly introverted, cannot be both highly neurotic and very stable. Similarly, one cannot be fascinated by social relationships such as to spend most of one’s time and energy on that matter, and at the same time fascinated by learning about abstract facts and figures and systems so as to spent most of one’s time and energy on that matter as well.

Most strong personality traits can, in principle, alternate in dominance over time and with circumstance – but they cannot dominate simultaneously. So it is an intrinsic property of E-S being descriptive of a personality trait that the predisposition towards one extreme of the trait is itself a predisposition away-from the other extreme.

 

However, the E-S personality traits have been persistently observed as different, on average, between men and women. And most of the most highly empathic people are women, while most high systemisers are men. This observation invites an evolutionary explanation. 

 

We suggest that the ultimate (evolutionary) cause of sex differentials in E-S lies in the ancestral sexual division of labour among humans; men and women having different characteristic roles: women focused child care and food gathering and preparation, men focused on whatever other tasks require doing: e.g. hunting, fighting, crafts(Lee & Daly, 1999; Lee & DeVore, 1968; Ridley, 1997).

 

Specifically, we regard Empathizing as a baseline state common to ancestral men and women, and Systemizing as having been selected-for at a later stage of human evolution, primarily among men due to the ancestral economic division of labour, and the economic benefits of having some men who are high Systemizers. We assume that there were significant material rewards for those men who were both able and willing to perform Systemizing tasks, and that these extra resources would have enhanced the survival of the offspring of successful Systemizers.

Evolution of the Systemizing trait

 

To recapitulate, the Empathizing trait refers to theory of mind abilities, which would be expected to be more evolutionarily ancient than the Systemizing trait, since they are found in non-human primates. Therefore a disposition towards Empathizing (theory of mind) are hypothesized to be a feature of pre-human primate and ancestral hunter-gatherer societies. We believe that Systemizing came later in human evolutionary history, and was an ability and disposition that (in a sense) displaced pre-existing Empathizing in some men.

 

By contrast, it is hard to see any need for, or evidence for, high levels of Systemizing trait in ancestral-type hunter gatherer societies, and it is hard to imagine a plausible benefit for a personality type which is characterized by high Systemizing. Ancestral hunter gatherers were (it is assumed) well-equipped by natural selection to deal with most of the non-personal/ ‘thing’-related problems they would encounter, since they had lived in the same type of environment for up to hundreds of generations. The social brain perspective suggests that the most cognitively-complex tasks our ancestors confronted were related to understanding, predicting and manipulating human social interactions (Byrne & Whiten, 1988). And for these problems, humans were prepared by their theory of mind abilities, and the ‘Empathizing’ personality was motivated to apply theory of mind abilities in relating to the world. 

 

Furthermore, ancestral hunter gatherers were generalists: apart from a sexual division of labour, essentially all women were involved in gathering and child care, all men were warriors and hunters. Any other activities needed to be fitted-around these requirements, but because the usual group size was small (probably around 15-35 including both the young and the old) there was only a little scope for specialization of function except in terms of sex and age (Charlton, 2000; Lee & Daly, 1999)

 

Systemizing abilities and interests seems likely to be most beneficial in post-agricultural, more complex, less ‘natural’ human societies. Indeed, agricultural societies are usually characterized by some degree of economic specialization - especially among men (Woodburn, 1982). This is necessary because of the greater need for learned knowledge and technology – agriculture is itself a specialist expert activity requiring not just invention but significant preservation and inter-generational transmission of knowledge (which is why it was not invented as a stable and continuing social form until the past 10-15,000 years)

 

The evolution of Systemizing can therefore be seen in the context of life history (Rushton, 1985). Woodley (2011) sees ancestral hunter gatherer societies as characterized by a relatively fast life history – with high fertility, rapid maturation of offspring and early maturity – and this leading to an un-specialized type of human – with a narrow range or ‘manifold’ of abilities. This situation may be associated with strong sexual selection – men investing on average little in their offspring but competing for multiple promiscuous matings (with uncertain paternity); presumably men would tend toward early maturity, high vigour and physical prowess, but a short life and a mainly social intelligence (e.g. men being charming rather than Systemizing).

 

By contrast, as agriculture emerged, and population density increased; it is probable that life history was slowed due to greater competition between humans (Woodley, 2011) In such a situation, men especially would seek a niche in which they could excel, and this would be associated with slower and later maturation – and a wider range (or manifold) of abilities between individuals - which meant that some people were better at one thing while other people were expert at different things. The trend would be towards lower fertility but higher level of parental investment per offspring – and the father contributing economic investment to their offspring (about which they would need have had a high degree of certainty of paternity for this behaviour to be adaptive; Wilson and Daly (1992), Charlton and McClelland (1999).

 

In ancestral ‘simple’ hunter gatherer societies there were probably a few tasks which focused on dealing with ‘things’ and where a personality preference for such tasks might be adaptive: problems such as navigating across a desert,  manufacturing a spear thrower or stone axe, or preparing poison for a bow and arrow. Typically such jobs require (in pre-literate societies) learning and precisely remembering an exact sequence of steps.

 

But such tasks are far more numerous, and more important, in agricultural societies where there is more technology, and where farming and the preparation and storage of food must be learned and repeated exactly year after year(Woodburn, 1982) . Such societies also typically develop specialists in religious ritual (priests) and in various crafts – and craft expertise in particular becomes absolutely essential to the survival of societies(Ingold, 2000; Ridley, 1997) .

Yet such crafts must be devised, remembered, and transmitted between generations. Our assumption is that it was this kind of selection pressure in agricultural societies which led to the evolution of high levels of Systemizing seen in some members of modern populations.

Systemizing was therefore a kind of expert ability and disposition; indeed Systemizing was exactly the trait that would enable expertise to develop; because expertise was (we infer) mostly a matter of learning and memorizing accurately precise sequential facts and procedures.  Thus the development of expertise is only partly about ability to perform a type of task – equally (or more) important is the personality which is motivated to do such tasks.

 

In other words, we suggest that until the development of agriculture, humans were originally towards the Empathizing end of the trait and that sexual differentiation was probably very limited; that the characteristic observed modern pattern of E-S is primarily a product of economic selection pressures following the development of agriculture; and furthermore that the sexual differentials in E-S are a consequence of historical differences in economic selection pressures as they operated on men and women since all ancient human societies display very considerable sexual specialization in terms of economic roles (Indeed, humans are among very few species exhibiting economic sex specialization;(Ridley, 1997).

 

We suggest, therefore, that the primary evolutionary cause of the range and reciprocity of E-S and also the higher average levels of S in men, was the sexual division of labour in a context of post-hunter gather economic systems. One implication is that men and women in hunter gatherer societies were probably more similar in the E-S dimension than are men and women in agricultural and post-agricultural societies (a prediction that may be partially-testable in modern descendants of these populations).

 

Sexual selection

 

Personality clearly affects sexual attractiveness, and may therefore be subject to sexual selection. On the one hand, common sense, personal observation and theoretical considerations suggest that, on average, women do not find the highly Systemizing personality (with its preference for things rather than people) to be (of itself) sexually attractive in men. On the other hand, female sexual preferences are not necessarily an important factor in determining sexual or marriage partners. Many human societies have not allowed much scope for individual female choice of sexual or marriage partners – for instance when young women are allocated to husbands as when marriages are arranged by parents, religious leaders or the wider community (Wilson & Daly, 1992). And in these societies, sexual selection, most often female choice, may be greatly attenuated or insignificant.

 

Individual sexual choice seems, in particular, to be very limited in most stable agricultural societies – and it is our assumption that it was precisely these stable agricultural societies in which the Systemizing trait is likely to have arisen and been amplified in men.

A further factor is that one of the most powerful factors affecting female sexual preference is male status. Insofar as a high Systemizing trait leads to higher status in a man, then it may be indirectly sexually attractive – unattractive in itself, but associated with a higher status that is attractive (Buss, 1995; Symons, 1980).

 

But – at the first level of analysis – we suggest that Systemizing trait may have arisen despite sexual selection, rather than because of it.

 

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If the Systemizing trait is probably (on average) unattractive to women, this suggests that - when women are allowed to choose freely, sexual selection probably works to reduce or eliminate the Systemizing trait. This would imply that – under modern conditions of independent femal choice of sexual and marriage partners, Systemizing would be under a negative selection pressure; and that this aspect of male personality may well be experiencing a ‘selective sweep’ in which the representation of the trait in the gene pool will be changing from one equilibrium towards another (Miller, 2010).

 

Another aspect is that a highly Systemizing disposition would presumably (like all personality traits) be substantially inherited by female children as well as male children – even when there are sex differentials (Miller, 2000). So that highly Systemizing trait women would become more common, as well as highly Systemizing men – simply as a by-product of the economic selection pressure on men.

 

Then, since Systemizing reflects a person’s interests, and shared interest may be a factor in mate choice; it would be expected that highly Systemizing women would tend to regard highly Systemizing men as relatively more attractive – especially if the woman was expecting to spend a lot of time with her husband. This would be a form of assortative mating, whereby sexual partners are chosen on the basis of similarity (Miller, 2009)  . And assortative mating between high Systemizers could plausibly be a mechanism by which ultra-high Systemizing might become a feature of populations – especially in men (Baron-Cohen, 2006). Therefore this is a plausible mechanism for the emergence of Asperger syndrome at a high frequency and severity – as a by-product of high Systemizing women choosing high systematizing men as partners.

 

Summary

 

Our hypotheses concerning the evolution of Empathizing can briefly be summarized:

1.      The baseline state is that (since humans are social animals) ancestral human hunter gatherers are assumed to be high Empathizers: more interested in people than in things.

2.      Economic changes, especially related to the development of agriculture, and also other technologically dependent societies (requiring complex tools, weapons, equipment, housing etc) mean that it becomes useful for some men to become more interested in things than in people, as a motivation for them to learn and practice socially vital skills.

3.      This selection pressure applies mainly to men since in the sexual division of labour it is typically men’s role to perform such tasks.

4.      The Systemizing trait is amplified by natural selection in men – perhaps by a neotenous mechanism where childhood traits are retained into adulthood. High Systemizers emerge: men who are spontaneously more interested in things than in people. 

5.      High Systemizers are rewarded for their socially vital work by high status (and supported with resources).

6.      Social arrangements develop (or already exist) that allocate women of high reproductive potential (young and healthy) to successful high Systemizers (for example by arranged marriages, dowry payments or bride price settlements) – these mechanism suppress or overcome the sexual selection mechanism by which women choose sexual partners or husbands who are Empathizers. 

7.      The marriages of economically successful high Systemizing men will experience greater-than-average reproductive success (with more surviving and viable offspring due to differentially increased access to economic resources such as food, shelter, technologies etc.) – thus amplifying the representation of genes that cause high systematizing in the population. 

 

Predictions

 

The theory has a number of testable predictions:

 

Systemizing may be undergoing (in developed societies) on the one hand assortative mating which amplifies the number of very high Systemizers (Baron-Cohen, 2006a); and on the other hand a selective sweep that is reducing the average level of S, due to the greater operation of sexual selection in the form of female sexual choice.

 

The male female difference in E- and S may have been less in hunter gather societies  than in agricultural or modern societies – and this may be measurable in the societies which have recently been hunter gatherers and have not yet experienced many generation of the selection effects of complex societies.

 

The theoretical model suggests possible methods of measuring Systemizing and Empathizing by developing instruments that quantify people’s spontaneous preferences as expressed in choices between focusing on either on people or else things.

 

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