Autism Spectrum Disorders

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Human Uniqueness Compared to "Great Apes": 
Absolute Difference
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Autism and Asperger syndrome are disorders of early childhood assumed to be developmental. Features include poverty of social interaction and the failure of communication, stereotypic behaviour, isolated special interests,  and resistance to change. Autism by definition emerges before age 3, Asperger's syndrome has a broader definition and includes problems of non-verbal communication more prominent than the langauge disorders seen in autism.

Both conditions reflect personality characteristics that are lifelong. The major etiologic contribution is held to be genetic. Sufferers are described as having deficits in "theory of mind", the ability to empathize with, and appreciate the presence, of other people. Other theories are that there is a failure of congenital gaze reflexes that ensure that the normal infant locks into the"ebb and flow" of social interaction, and that there is a failure of the mechanism whereby normal individuals allocate incoming information to a "relevant" context in memory.

Timing

Timing of appearance of the difference in the Hominin Lineage as a defined date or a lineage separation event. The point in time associated with lineage separation events may change in the future as the scientific community agrees upon better time estimates. Lineage separation events are defined in 2017 as:

  • the Last Common Ancestor (LCA) of humans and old world monkeys was 25,000 - 30,000 thousand (25 - 30 million) years ago
  • the Last Common Ancestor (LCA) of humans and chimpanzees was 6,000 - 8,000 thousand (6 - 8 million) years ago
  • the emergence of the genus Homo was 2,000 thousand (2 million) years ago
  • the Last Common Ancestor (LCA) of humans and neanderthals was 500 thousand years ago
  • the common ancestor of modern humans was 100 - 300 thousand years ago

Possible Appearance: 
2,000 thousand years ago
Probable Appearance: 
100 thousand years ago
Definite Appearance: 
1 thousand years ago
Background Information: 

Autism and Asperger syndrome were described in 1943 and 1944 by Leo Kanner and Hans Asperger respectively and include many overlapping features. For example poverty of social interaction and the failure of communication, stereotypic behaviour, isolated special interests, outstanding skills and resistance to change. Kanner first described language peculiarities, such as echolalia, pronoun reversal and difficulties in generalising word meanings. Asperger described ' clever sounding ' language, invented words and adult-like speech. He also identified abnormalities of non-verbal communication, for example of eye gaze, gesture, posture, voice quality, prosody and word choice. He emphasized lack of humor and pedantry.   The boundary between the conditions is not well-defined.   With respect to etiology twin and family studies suggest a genetic component common to the two conditions.   Alan Leslie proposed a "theory of mind" hypothesis that Humans have the ability to distinguish first-order from second-order representations and that this allows them to separate representations of physical and mental states, and thus to impute the existence of "other minds". The same ability allows them to engage in play, and the pretence involved in collaborative games and story-telling.

The Human Difference: 

If the phenomena of the autistic spectrum are intrinsically related to the human capacity for secondary representation, or theory of mind, which in turn may reflect the change that enabled the capacity for language, only humans will be expected to have the spectrum of personality and cognitive variation that underlies the spectrum. The occurrence of special abilities (eg with respect to memory, mental calculation, & drawing) strongly suggests that the basis of these anomalies is related to specifically human abilities, and therefore that we are dealing with genetic variation that separates H sapiens from other primate species.

Universality in Human Populations: 

Accurate cross-cultural data are not available but autistiic spectrum individuals are identified in all cultures with similar features.

Mechanisms Responsible for the Difference: 

Increased brain size and decreased corpus callosum area are reported in autistic spectrum disorder, compatible with a late developmental deviation.

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References

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