Transcript Schizophrenia: An Evolutionary Perspective

Schizophrenia: An
Evolutionary Perspective
By: Tanya Kraus
Schizophrenia
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a psychotic disorder characterized by
major disturbances in thought, emotion, and
behaviour – disordered thinking in which
ideas are not logically related, faulty
perception and attention, flat or
inappropriate affect, and bizarre
disturbances in motor activity. Patients with
schizophrenia often withdraw from people
and reality into a fantasy life of delusions
and hallucinations.
Positive/Negative Symptoms
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Positive symptoms: Involves behaviour that
is not normally present in most people. (E.g.
distortions, disorganized speech,
hallucinations, or delusions.)
Negative symptoms: Involves behavioural
deficits that are not present in most people.
(E.g. avolition, alogia, anhedonia, flat affect,
and asociality.)
Other Symptoms
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Many patients experience the following
as well as positive and negative
symptoms.
Catatonia: Defined by several motor
abnormalities, which can include
catatonic immobility or waxy flexibility
Inappropriate Affect: Emotional
responses that are out of context
Here’s Where the Evolution Part
Becomes Relevant…
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Unusual behaviours that strongly resemble
schizophrenia have dated back to Mesopotamia
Universally, the prevalence rate of schizophrenia
is about 1%, which exceeds common mutation
rates
There is a strong genetic component (E.g. twin and
adoption studies)
Conditions such as schizophrenia have a long
history and a strong genetic base, meaning
evolutionary explanations must be acknowledged
Evolution Perspectives
Evolutionary perspectives can be divided
into two groups:
a) Theories that assume schizophrenia
is a disadvantageous by-product of
human brain evolution
b) Theories that consider schizophrenia
to have an evolutionary advantage
Schizophrenia: Disadvantageous ByProduct of Human Brain Evolution
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Theory #1: Farley’s argument that
schizophrenia could be an extreme
variant of normal social behaviour
Flaw: This theory fails to explain why
schizophrenia is comprised of both
negative and positive symptoms
Disadvantages, Cont.
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Theory #2: Randall’s novel neural
pathways model…”biological trial and error
of connection would produce a range of
behavioural variants, including
schizophrenia.”
Flaw: Denies the specific symptoms that
occur in any given disorder, as well as the
maintenance of pathology
Disadvantages, Cont.
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Theory #3: Saugstad’s pathophysiological
model, which connects many frontal lobe
disorders (E.g. schizophrenia, infantile
autism), to delayed cerebral maturation.
Again, schizophrenia is viewed simply as an
outlier within the normal bounds of variation
Flaw: It would be atypical for nature to
produce such large numbers of distinct
phenotypes with reduced fecundity (Ability
to produce many children)
Disadvantages, Cont.
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Theory #4: Yeo and the
developmental instability model of
schizophrenia
Flaw: While being a very intriguing
theory, it lacks any empirical evidence
at this point in time. It should be
considered speculatively
Schizophrenia as an
Evolutionary Advantage
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Schizophrenia paradox: “The
discrepancy between high prevalence
rate and reduced fecundity”
This doesn’t seem very adaptive, does
it?
There must have been some
evolutionary advantage to having
schizophrenia…
Advantageous Theories
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Theory #1: Huxley, Mayr, Osmond, and
Hoffer published the first model linking
schizophrenia to evolutionary concepts.
(1964) Speculated that reduced fecundity
was compensated by higher resistance to
allergens, shock, and infection
Flaw: No substantial evidence supporting
this theory
Advantageous, Cont.
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Theory #2: Kellet’s model suggesting that
certain characteristics found in
schizophrenia may have helped man’s
territorial instincts
Flaw: This theory addresses only a small
component of schizophrenia, providing no
evolutionary explanation for psychotic
symptoms
Advantageous, Cont.
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Theory #3: The schizophrenia gene could possibly
benefit individuals who carry it but do not have the
disorder
Karlsson studied a population of schizophrenics in
Iceland and discovered that first-degree relatives
were twice as likely to be members of creative
professions than the general population
Flaw: Providing an accurate association between
psychiatric conditions and creativity can be difficult
Conclusion
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Although there are many theories regarding
the origins and possible evolutionary
advantages/disadvantages of schizophrenia,
none of them have truly been proven
Up until the 1960’s, studying schizophrenia
from an evolutionary perspective was
unheard of. However, this can only add to
our understanding of this severe disorder
and will hopefully one day benefit those
who suffer from schizophrenia
The End!