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evolutionary advantages of adhd traits

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evolutionary advantages of adhd traits

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    1. First we are going to present an e-book written for the general public which presents Attention deficit hyperactivity disorder also known as ADHD as an evolutionary trait, and we will then discuss the theories that both support and challenge this view.First we are going to present an e-book written for the general public which presents Attention deficit hyperactivity disorder also known as ADHD as an evolutionary trait, and we will then discuss the theories that both support and challenge this view.

    24. Traits of ADHD Today Attention-Deficit / Hyperactivity Disorder Attention Problems Hyperactivity Impulsivity Impairment in ability to delay gratification ADHD stands for Attention Deficit Hyperactivity Disorder – sounds like your average child, but really is not! Symptoms are at a more persistant and severe level than the child’s developmental peers. Symptoms of the disorder are classed along three main axis within the DSM-IV – these are inattentive symptoms, hyperactivity and impulsivity. Egs of inattentive symptoms include jumping from one task to another, quick shifts in conversational topics, avoidance of tasks requiring sustained mental effort, and the child is easily distracted by irrelevant stimuli such as fire trucks going by, or a person mowing the lawn while they are in class. Hyperactivity problems include excessive fiddling, shaking and fidgetting while trying to sit still, and excessive running, jumping and climbing in situations where it is just not appropriate, or excessive talking in quiet places, or times. Impulsive symptoms include a difficulty in delaying responses, a difficulty in waiting turn, engagement in potentially dangerous activities due to not considering the consequences – due to these symptoms and others, impulsivity can often manifest itself as impatience. The delay of gratification impairment is significant – ADHD children will take an smaller instant rewards over a larger but later reward – however, they are not unlike the general population in this respect as anyone in Alan Lewis’ lecture will know – almost all ppl in the general population will take the smaller but sooner alternative. However, the ADHD child’s impairment means that they often have problems with motivation as a distant gain does not appeal to them e.g. you and I will write our dissertations, especially on the 6th May, despite really not wanting to , and wanting to go for a pint instead - because we can see the long term benefit it will bring us – ADHD children can’t do that.ADHD stands for Attention Deficit Hyperactivity Disorder – sounds like your average child, but really is not! Symptoms are at a more persistant and severe level than the child’s developmental peers. Symptoms of the disorder are classed along three main axis within the DSM-IV – these are inattentive symptoms, hyperactivity and impulsivity. Egs of inattentive symptoms include jumping from one task to another, quick shifts in conversational topics, avoidance of tasks requiring sustained mental effort, and the child is easily distracted by irrelevant stimuli such as fire trucks going by, or a person mowing the lawn while they are in class. Hyperactivity problems include excessive fiddling, shaking and fidgetting while trying to sit still, and excessive running, jumping and climbing in situations where it is just not appropriate, or excessive talking in quiet places, or times. Impulsive symptoms include a difficulty in delaying responses, a difficulty in waiting turn, engagement in potentially dangerous activities due to not considering the consequences – due to these symptoms and others, impulsivity can often manifest itself as impatience. The delay of gratification impairment is significant – ADHD children will take an smaller instant rewards over a larger but later reward – however, they are not unlike the general population in this respect as anyone in Alan Lewis’ lecture will know – almost all ppl in the general population will take the smaller but sooner alternative. However, the ADHD child’s impairment means that they often have problems with motivation as a distant gain does not appeal to them e.g. you and I will write our dissertations, especially on the 6th May, despite really not wanting to , and wanting to go for a pint instead - because we can see the long term benefit it will bring us – ADHD children can’t do that.

    25. ADHD as a ‘different’ but not ‘deficit’ profile Human’s ancestors lived for a few million years in hunter-gather societies. Dramatic change in the last 10,000 years However because of the rapid rate of change evolution of the human genome has not caught up. Hunter in a farmers world 1) Hunter in a farmer’s world: ADHD as a ‘different’ but not ‘deficit’ profile: not only weaknesses but also strengths. Disorder model of ADHD proposed by Barkley and others assumes that there is one single, superior (non ADHD) way of behaving and being in the world, in all times and cultures. The difference perspective: different people use different techniques to achieve the same goals. Different ways of remembering, for example although ‘hunters’ may have poor rote memories they are able to take advantage of their ‘superior’ incidental memories. They are more likely to recall and use background information Disorder and adaptation are not opposites – characteristic that is seen as a disorder in one context may be adaptive in another. Hunter and farmer are two end points on a continuum of human variability ‘Hunter gene’ and ‘Farmer gene’ have both always been present – always a need for the ‘adventurous explorer’ and the ‘careful bookkeeper’ 1) Hunter in a farmer’s world: ADHD as a ‘different’ but not ‘deficit’ profile: not only weaknesses but also strengths. Disorder model of ADHD proposed by Barkley and others assumes that there is one single, superior (non ADHD) way of behaving and being in the world, in all times and cultures. The difference perspective: different people use different techniques to achieve the same goals. Different ways of remembering, for example although ‘hunters’ may have poor rote memories they are able to take advantage of their ‘superior’ incidental memories. They are more likely to recall and use background information Disorder and adaptation are not opposites – characteristic that is seen as a disorder in one context may be adaptive in another. Hunter and farmer are two end points on a continuum of human variability ‘Hunter gene’ and ‘Farmer gene’ have both always been present – always a need for the ‘adventurous explorer’ and the ‘careful bookkeeper’

    26. So what were hunter societies like…

    27. Ranged along several continuum: Safe versus dangerous Resource rich verses Impoverished Time optional verses time critical Therefore ‘hunter’ gene advantageous in ‘response ready’ environments where as in ‘problem solving’ environments ‘farmer’ gene more adaptive. Need for both skills in all societiesRanged along several continuum: Safe versus dangerous Resource rich verses Impoverished Time optional verses time critical Therefore ‘hunter’ gene advantageous in ‘response ready’ environments where as in ‘problem solving’ environments ‘farmer’ gene more adaptive. Need for both skills in all societies

    28. Adaptive Functions 3) Adaptive properties of ADHD (Adapted from http://www.mythical.net/hunterfarmer.shtml)No time for niceties Lacking in social graces Takes risks & faces dangerImpulsiveLike new ideas, excitement Day dreamerIndependentDifficulty following instructionsTireless: capable of sustained drives but only when hot on the chaseImpatient Throw themselves into the chase at a moments noticePoor planner – impulsive Constantly monitoring the environment Sort attention spans & hyperfocusingEvolutionary advantageTrait associated with ADHD Hyperactivity - constantly exploring the environment for threats and opportunities Attentional processes - over focused attention could be maladaptive in high-threat environments. Definitions of over or under attention are sensible only when situated within a given context and for specific classes of stimuli. Impulsivity – necessary to respond to possible predators or pray quickly or the opportunity map be missed with sever consequences. 3) Adaptive properties of ADHD (Adapted from http://www.mythical.net/hunterfarmer.shtml)No time for niceties Lacking in social graces Takes risks & faces dangerImpulsiveLike new ideas, excitement Day dreamerIndependentDifficulty following instructionsTireless: capable of sustained drives but only when hot on the chaseImpatient Throw themselves into the chase at a moments noticePoor planner – impulsive Constantly monitoring the environment Sort attention spans & hyperfocusingEvolutionary advantageTrait associated with ADHD

    29. Criteria for a function to be classed as adaptive Recurring characteristics over generations. Is present throughout the individual’s life time. Genetic basis. Develops in a ‘normal’ environment. Interacted with ancestral environment – ‘the adaptive problem’. Offered best solution – so genetically selected. By enhancing the reproduction of the individual. 4) Criteria for a function to be classed as adaptive ADD/ADHD in adults: http://www.nmha.org/infoctr/factsheets/93.cfm While the condition is most often associated with children, there has been a more recent understanding the Attention Deficit Disorders (ADD, ADHD) continue into adulthood for many individuals. Symptoms such as inattention, impulsivity and over activity are now known to continue into adulthood for a significant percentage of children with ADD. Unfortunately, relatively few adults are diagnosed or treated for ADD. Cross cultural studies have found ADD/ADHD in Australia, New Zealand, Germany, USA & Hong Kong [1]4) Criteria for a function to be classed as adaptive ADD/ADHD in adults: http://www.nmha.org/infoctr/factsheets/93.cfm While the condition is most often associated with children, there has been a more recent understanding the Attention Deficit Disorders (ADD, ADHD) continue into adulthood for many individuals. Symptoms such as inattention, impulsivity and over activity are now known to continue into adulthood for a significant percentage of children with ADD. Unfortunately, relatively few adults are diagnosed or treated for ADD. Cross cultural studies have found ADD/ADHD in Australia, New Zealand, Germany, USA & Hong Kong [1]

    30. Does ADHD meet these criteria Occurs across generations. Present in adulthood. Cross cultural studies show that it is universal. The characteristics of ADHD are adaptive and therefore would promote the propagation of the ‘hunter gene’: More opportunities for mating More likely to survive long enough ADHD prevalence of 3-5% as cited in the DSM-IV suggests that it must have been selected for genetically.ADHD prevalence of 3-5% as cited in the DSM-IV suggests that it must have been selected for genetically.

    31. The Genetics of ADHD Both: DRD4 (dopamine receptor) SLC3A6 (dopamine transporter) reported in molecular genetic studies as linked with ADHD. One of the most replicated links in psychiatric genetics. (Maio, Grizenko and Joober, 2003). ADHD is polygenetic. If ADHD is the result of an evolved ‘hunter sense’ then it would need to be transmitted through the genes. Maio, Grizenko and Joober’s review of genetic studies surrounding ADHD found that the dopamine receptor DRD4 and the dopamine transporter, SLC3A6 (catchy name!) were both found to be linked with ADHD, and that the link between dopamine and ADHD was one of the most replicated links in psychiatric genetics. The connection of the condition ADHD with Dopamine makes considerable sense when the psychostimulants children are given for treatment actually inhibit the dopamine transporter and increase synaptic levels of dopamine. Other dopamine transporters and receptors have also been implicated in studies but due to time constraints we have chosen to focus on these particular ones – if you would like more information on the other implicated links I can email you Maio et al’s paper, the main point is that ADHD is a polygenetic disorder i.e. it has several genes contributing to its existence.If ADHD is the result of an evolved ‘hunter sense’ then it would need to be transmitted through the genes. Maio, Grizenko and Joober’s review of genetic studies surrounding ADHD found that the dopamine receptor DRD4 and the dopamine transporter, SLC3A6 (catchy name!) were both found to be linked with ADHD, and that the link between dopamine and ADHD was one of the most replicated links in psychiatric genetics. The connection of the condition ADHD with Dopamine makes considerable sense when the psychostimulants children are given for treatment actually inhibit the dopamine transporter and increase synaptic levels of dopamine. Other dopamine transporters and receptors have also been implicated in studies but due to time constraints we have chosen to focus on these particular ones – if you would like more information on the other implicated links I can email you Maio et al’s paper, the main point is that ADHD is a polygenetic disorder i.e. it has several genes contributing to its existence.

    32. SLC3A6 and ADHD Consistent with psychostimulant treatment. Knock-out mice Spontaneously hyperactive Higher levels of motor activity Significantly calmed by amphetamines The connection of the condition ADHD with Dopamine makes considerable sense when we consider the psychostimulants children with the disorder are given for treatment Methylphenidate the most commonly prescribed medication for ADHD actually inhibits the function of this dopamine transporter by preventing pre-synaptic reuptake of dopamine. Studies were carried out using genetically modified mice that had had this dopamine transporter ‘knocked-out’ of them. The mice were found to be spontaneously more hyperactive and displayed higher levels of motor activity under stress in comparison to their ‘wild’ counterparts. They were also significantly calmed by the administration of amphetamines and methylphenidate – thereby replicating the paradox of ADHD treatment. The connection of the condition ADHD with Dopamine makes considerable sense when we consider the psychostimulants children with the disorder are given for treatment Methylphenidate the most commonly prescribed medication for ADHD actually inhibits the function of this dopamine transporter by preventing pre-synaptic reuptake of dopamine. Studies were carried out using genetically modified mice that had had this dopamine transporter ‘knocked-out’ of them. The mice were found to be spontaneously more hyperactive and displayed higher levels of motor activity under stress in comparison to their ‘wild’ counterparts. They were also significantly calmed by the administration of amphetamines and methylphenidate – thereby replicating the paradox of ADHD treatment.

    33. DRD4 and ADHD DRD4 has approximately 10 different versions (alleles). The 7R allele is associated with ADHD. 7R has a prevalence rate of 20.6% in the general population (Maio et al. 2003) People with ADHD are nearly twice as likely to have the 7R allele than non-ADHD individuals. (Faraone et al, 2001) The DRD4 has approximately 10 different versions – with allele 4-repeat, 2-repeat and 7-repeat being the most common in the population. The high prevalence rate of the 7R allele is argued by Maio et al. to indicate that this particular allele may play an important role at a population level, supporting an evolutionary explanation for the disorder as an advantageous characteristic – may have only been a few hunters in the stone age that had this characteristic, only a few needed to reap benefits – would not want all hunters to be ADHD. DRD4 has been connected with novelty seeking by Paterson et al. (1999) which fits nicely with the hunter theory of ADHD, while supporting the dopamine role in the genetic transmission of the disposition.The DRD4 has approximately 10 different versions – with allele 4-repeat, 2-repeat and 7-repeat being the most common in the population. The high prevalence rate of the 7R allele is argued by Maio et al. to indicate that this particular allele may play an important role at a population level, supporting an evolutionary explanation for the disorder as an advantageous characteristic – may have only been a few hunters in the stone age that had this characteristic, only a few needed to reap benefits – would not want all hunters to be ADHD. DRD4 has been connected with novelty seeking by Paterson et al. (1999) which fits nicely with the hunter theory of ADHD, while supporting the dopamine role in the genetic transmission of the disposition.

    34. Nature via Nurture ADHD has a genetic base. This does not refute the influence of social factors. Higher prevalence rates in deprived areas (studies cited in Taylor) Genetic behaviours are occurring due to an environmental cue. (Ridley, 2003) ADHD genes may therefore be being ‘activated’ by certain social conditions such as psychosocial disadvantage, and lack of resources – this would make sense if an evolutionary model were instilled as a hunter would be useful in situations where resources are scarce, therefore makes sense that these genes would be activated by such conditions. But, this may again fall under Darwinian storytelling.ADHD genes may therefore be being ‘activated’ by certain social conditions such as psychosocial disadvantage, and lack of resources – this would make sense if an evolutionary model were instilled as a hunter would be useful in situations where resources are scarce, therefore makes sense that these genes would be activated by such conditions. But, this may again fall under Darwinian storytelling.

    35. Is ADHD an Adaptation? It is extremely unlikely that ADHD could have evolved and been maintained by chance alone. ADHD effects functioning + ADHD is a complex disorder = ADHD is an Adaptation

    36. Are we just telling Darwinian stories? Can we really ‘reverse engineer’ the mind? It is possible to create such an explanation for anything –Females took longer to come down from the trees! ‘Just so stories’ (Goldstein 1998) claim that the ‘romantic’ idea of ADHD as an old evolutionary trait is nothing but fiction. ADHD not adaptive in any context. Does not fit with evolutionary theory. Are we just telling Darwinian stories? First, it was noticed recently that some of our female ancestors in Africa had smaller leg bones and a different ankle structure than the males, suggesting to modern scientists that women came to ground from the trees long after the males did. Observers next watched American children on playgrounds; surprisingly, the girls at age 6 climb higher on monkey bars than boys of the same age. Finally, giving young children in Israel or the United States a simulated escape game revealed that girls more often than boys choose to climb trees and climb further out on the branches in order to get away from predators. Israeli girls also climbed higher on the simulated Acacia tree after a coincidental but real terrorist attack. Psychologists can infer the evolutionary purpose of behaviours and mental modules by studying when they come into play in daily life and how they increase reproductive success. Pinker has never met an adaptive tale he doesn’t likeAre we just telling Darwinian stories? First, it was noticed recently that some of our female ancestors in Africa had smaller leg bones and a different ankle structure than the males, suggesting to modern scientists that women came to ground from the trees long after the males did. Observers next watched American children on playgrounds; surprisingly, the girls at age 6 climb higher on monkey bars than boys of the same age. Finally, giving young children in Israel or the United States a simulated escape game revealed that girls more often than boys choose to climb trees and climb further out on the branches in order to get away from predators. Israeli girls also climbed higher on the simulated Acacia tree after a coincidental but real terrorist attack. Psychologists can infer the evolutionary purpose of behaviours and mental modules by studying when they come into play in daily life and how they increase reproductive success. Pinker has never met an adaptive tale he doesn’t like

    37. Continued…… Executive Function - Goldstein’s Model Hunter-gatherer - Evolutionary Model Self regulation and executive function on a normal distribution curve Qualities of ADHD place individuals at the lower tail of an adaptive bell curve for Self-regulation & executive function. Self regulation and executive function on a normal distribution curve Qualities of ADHD place individuals at the lower tail of an adaptive bell curve for Self-regulation & executive function.

    38. Or is ADHD a ‘spandrel’? Gould and Lewontin, 1979 Triangles are byproducts of the arches being present – ADHD could simply be a byproduct of the genes that are available. Gould criticises evolutionary psychologists for seeing design when it is simply architectural constraint – he states that they see adaptive function – in this example the decoration in the triangles - in situations where there is a more parsimonious explanation – in this example the fact that the arches exist creates these triangles – there is no other purpose behind their existence. Gould states the fact we are looking at biology rather than buildings biases us against recognising these architectural constraints. But that does not aid treatment for the people who suffer from this disorder, and this is a significant consideration. Triangles are byproducts of the arches being present – ADHD could simply be a byproduct of the genes that are available. Gould criticises evolutionary psychologists for seeing design when it is simply architectural constraint – he states that they see adaptive function – in this example the decoration in the triangles - in situations where there is a more parsimonious explanation – in this example the fact that the arches exist creates these triangles – there is no other purpose behind their existence. Gould states the fact we are looking at biology rather than buildings biases us against recognising these architectural constraints. But that does not aid treatment for the people who suffer from this disorder, and this is a significant consideration.

    39. Just-so-so-Stories Natural Selection does not mean an organism will be optimal. Natural Selection means that things that are only slightly advantageous will be kept. Therefore, the Hunter of the past would not have been the perfect hunter. ADHD may have held some advantages for a hunter in the past. Adaptations in nature are not perfect – in fact this is what the case for ADHD hangs on – that a time lag in adaptation is what is causing ADHD to be classified as a disorder. Other constraints on adaptations exist such as the genetic constraints previously discussed in the spandrels argument, but also, developmental constraints i.e. the way an organism develops will influence the kinds of mutation it is likely to generate. Historical constraints – where historical conditions may have led evolution in a direction which would later become detrimental or lead it to stagnation – natural selection does not have foresight and so can not do anything but select for what is advantageous in that particular time and environment. Trade-offs between different adaptive needs i.e. our brain has evolved to perform more than one function, and therefore its development will represent a compromise between the needs of each of these functions.Adaptations in nature are not perfect – in fact this is what the case for ADHD hangs on – that a time lag in adaptation is what is causing ADHD to be classified as a disorder. Other constraints on adaptations exist such as the genetic constraints previously discussed in the spandrels argument, but also, developmental constraints i.e. the way an organism develops will influence the kinds of mutation it is likely to generate. Historical constraints – where historical conditions may have led evolution in a direction which would later become detrimental or lead it to stagnation – natural selection does not have foresight and so can not do anything but select for what is advantageous in that particular time and environment. Trade-offs between different adaptive needs i.e. our brain has evolved to perform more than one function, and therefore its development will represent a compromise between the needs of each of these functions.

    40. Does America have ADHD? ‘We are a supermobile hyperconected, media-saturated society’ (U.S. News) News sound bite – 43s to 8s TV ads from 53s to 25s 15s ads are common place 201 messages a day

    41. Does America have ADHD? Start more projects than you finish, hate waiting in traffic, chronically late – sound familiar? Forced to give ‘continuous partial attention’ If we took control & filtered all the information we receive would ADHD disappear ?

    42. Modern Hunters Modern hunters show ADHD behaviours. (Krynen cited in Hartmann, p59-60) Therefore symptoms can not be totally created by things such as advertising . Advertising and other social factors may serve to ‘activate’ the gene(s) responsible for ADHD.

    43. Conclusions Positive view of people who would previously be perceived as disordered. Clinical value. Proof that it is not just a present day phenomenon. The pieces of the Jigsaw fit. BUT is this enough?

    44. References American Psychiatric Association. (1994). Diagnostic and statistical manual of mental disorders. (4th ed.) New York: The Psychological Corporation. Faraone, S. , Doyle, A. E. , Mick, E. & Biederman, J. (2001) Am. J. Psychiatry 158, 1052-1057. Foust, S.J. (1994) Notes from Dr. Barkley's ADHD seminar. [Online] Available at http://users.rcn.com/peregrin.enteract/add/barkley.html (accessed February 13, 2004). Goldstein, S. and Barkley, R.A. (1998). ADHD, hunting and evolution: ‘just so’ stories. ADHD Report. 6(5), pp.1-4. Gould, S.J. and Lewontin, R.C. (1979). The spandrels of San Marco and the Panglossian paradigm: a critique of the adaptionist programme. Proc. R. Soc. Lond. 205, pp.581-598. Hartmann, T. (1996). Beyond ADD: hunting for reasons in the past and present. California: Underwood Books. Hensby, C. and Braham, B. Hunter of the past. [Online] Available at: www.adders.org/freeware/hunter.htm/ (accessed February 13, 2004)

    45. References continued Jensen, P.S., Mrazek, D., Knapp, P.K., Steinberg, L., Preffer, C., Schowalter, J., Shapiro, T. (1997). Evolution and revolution in child psychiatry: ADHD as a disorder of adaptation. Journal of the American Academy of Child and Adolescent Psychiatry, 36(12), pp.1672-1679. Maio, S., Grizenko, N. and Joober, R. (2003). Dopamine genes and attention-deficit hyperactivity disorder: a review. Journal of Psychiatry and Neuroscience, 28(1), pp. 27-38. Orr, H.A. (2003, Feb 27). Darwinian storytelling. The New York Review. Pp. 17-20. Pinker, S. (2002). The blank slate. London: Penguin Books. Ridley, M. (2003). Nature via nurture: genes, experience and what makes us human. London: Fourth Estate. Schachar, R., and Sergeant, J.A. (2002). Classification issues. In: Sandberg, S. ed. Hyperactivity and attention disorders of childhood, 2nd ed., pp. 126-161. Cambridge: Cambridge University Press. Taylor, E. (1995). Syndromes of Attention Deficit and Overactivity. In: Child and Adolescent Psychiatry: modern approaches. 3rd ed. (Rutter, M., Taylor, E., Hersov, L., ed.s), pp. 285-304. Oxford: Blackwell Science. Zuckerman, M.B. (2001). Does America have ADD? U.S. News, 26th March, pp. 14

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