Transcript EVOLUTIONARY PSYCHOLOGY, SESSION 6: MALE MATE …

Evolutionary Psychology Lecture 11:
Health & Psychopathology.
Learning Outcomes.
 At the end of this session you should be able to:
 1. Evaluate the adaptive benefits of pregnancy
sickness.
 2. Discuss evolutionary explanations for certain
pathological behaviours.
Levels of Explanation.
 In the past medicine and psychiatry have attempted to
explain physical and behavioural disorders, and to seek
appropriate treatments for those disorders based on
straightforward considerations of anatomy and physiology.
 These are proximate explanations.
 In contrast, the relatively new field of Darwinian
medicine/psychiatry focuses upon:
 The way the body is designed that make it vulnerable to
certain disorders and ailments.
 The operation of adaptations that may once have served a
useful purpose but the operation of which may now result
in maladaptive or pathological consequences in modern
environments.
 These are ultimate explanations.
1. Health & Illness
 According to Nesse & Williams (1998) we can place
evolutionary explanations for disease in several categories.
 Of key importance is that some discomforting conditions
(pain, fever, coughing, sneezing, diarrhoea, inflammation,
nausea, anxiety etc), are not diseases or design faults.
 Instead they are evolved defences aimed at prolonging the
reproductive fitness (survival) of the individual.
 E.g, a high temperature is assumed to reflect a dangerous
side effect of invasion by pathogens, which should be
reduced.
 However, fever is a carefully regulated rise in the set point
of the body's thermostat and a rise in temperature will
facilitate pathogen destruction; reducing the temperature
by drugs may actually prolong the illness.
Example: Pregnancy Sickness
 Pregnancy sickness (or nausea and vomiting during
pregnancy - NVP) is a collection of symptoms (food
aversions, nausea, and vomiting) which occur during the
first trimester (first 3 months) of pregnancy.
 Many smells and tastes that women normally find palatable
become intolerable to them; and these smells or tastes can
trigger nausea and vomiting.
 This condition has been viewed by the standard medical
account as an uncomfortable by-product of the hormonal
alterations of pregnancy.
 From an evolutionary perspective, one can however focus
on the possible defence mechanisms and thus the adaptive
benefits that NVP might serve (Profet, 1992).
Benefits of NVP?
 It is at first difficult to see
how feeling ill during
pregnancy can benefit the
mother or her embryo.
 However, Klebanoff et al.,
(1985) found that women
who experienced severe
nausea and vomiting in the
first trimester had much
lower risks of having a
miscarriage.
From Flaxman & Sherman, 2000)
Toxin Avoidance.
 Plants, vegetables and fruits manufacture toxins to poison
their predators.
 Such toxins exist in plants normally considered harmless
and which form an integral part of a healthy diet e.g.
apples, bananas, celery, cabbage, brussel sprouts, parsnips,
cherries, oranges.
 Many plant toxins smell or taste bitter or pungent (e.g.
onions), and animals have developed chemoreceptors in
the nose and tongue to detect these toxins.
 The levels of these toxins are very low, and will only affect
adults in large doses, however small doses are very
dangerous to embryos.
 E.g Potato’s contain high levels of toxins which can cause
neural tube defects in the embryos of mammals (Renwick
et al., 1984).
Pregnancy Sickness as An Adaptation.
 Pregnancy sickness coincides with organogenesis - the
embryonic period of maximum vulnerability to teratogens
(environmental poisons), 20-56 days after conception.
 Pregnancy sickness begins 2-4 weeks after conception, peaks
at 6-8 weeks, and falls off after 8 weeks, (the end of
organogenesis).
 It is not present in the first 2 weeks as the embryo has not
yet formed a placenta.
 Sickness is unnecessary after organogenesis as the foetus is
much less susceptible to teratogens.
 The nutritional costs of sickness are low because ovulation
and conception does not occur unless the female has
accumulated a certain threshold of fat reserves (Frisch,
1987).
From Flaxman & Sherman, 2000, p 123.
Why Create an Aversion to Vegetables?
 It seems odd that pregnancy sickness should cause an
aversion to vegetables which are rich in folates and other
vitamins essential to normal embryonic development.
 However, our ancestors would not have been vitamin
deficient at conception because much of their calorific
intake came from vegetables and fruits.
 Folates are stored in the liver for 4 months and so would
have covered the temporary deficiencies experienced
during pregnancy sickness.
 Modern women are low in folates and are thus particularly
susceptible to folate deficiency (Eaton & Konner, 1985).
Olfactory Cues.
 Pregnancy sickness heightens smell and taste sensitivity.
 This induces food aversions and vomiting with little
provocation.
 Vegetable toxins produce pungent aromas and so provide
good clues about their possible dangers.
 Non-plant foods also produce olfactory cues, e.g pungency
in meat and dairy products is a sign of parasitisation by
bacteria.
 The best-tolerated foods should be those which are bland
and do not spoil easily (bread, cereals etc). Studies
analysing food aversions show that women have the
strongest aversions to tea, coffee, vegetables and meat and
have little or no aversions to bread and cereals (Flaxman &
Sherman, 2000).
Evolutionary Novel Toxins.
 However, evolutionary novel toxins lack such perceptual
triggers and fail to elicit the symptoms of pregnancy
sickness.
 Many modern drugs are derivatives of plant toxins and are
very potent; however they are typically delivered in pills
and injections which do not give off volatile odours or
tastes.
 Studies of food aversion show that strong alcohol aversion
is much less pronounced than are strong food aversions, as
the main component of alcohol (ethanol) is a non-bitter
chemical.
 Alcoholic drinks containing bitter-tasting plant constituents
(e.g. whiskey, wine) are more aversive in pregnancy than
ones with no such extracts (e.g. vodka).
Flaxman & Sherman (2000).
 They reviewed the theory that pregnancy sickness acts as
an adaptation, and confirmed that:
 Symptoms peak when embryonic organogenesis is most
susceptible to chemical disruption.
 Women who experience morning sickness are significantly
less likely to miscarry.
 Women who vomit suffer fewer miscarriages than those
who experience nausea alone.
 Many pregnant women have aversions to alcoholic and
caffeinated drinks, and strong-tasting vegetables, though
the greatest aversions are to meat, fish, poultry and eggs.
This is because animal products are especially dangerous as
they contain pathogens and parasites.
Food Aversions and Cravings.
Meat N-A drinks Veg
Alcohol
Spicy
Dairy
Sweets Grains Fruits
From Flaxman & Sherman, 2000 p 127.
Psychopathology.
 Crawford & Salmon (2002) hold two views of
psychopathology:
 1. It is a neurodevelopmental disorder (physical cause).
 2. It could represent the activation of strategies that may
once have been adaptive but which now are maladaptive.
 Nesse & Willams (1995) noted that certain pathologies may
be perpetuated by genetic mechanisms, because:
 Their effects were beneficial in ancestral environments (e.g.
preference for high calorie foods - which now leads to
obesity and illness).
 Genes that influenced disease expression may also have
had benefits in certain environments (e.g. sickle-cell
anaemia and malaria protection).
 Such explanations might also be true for psychopathological
conditions.
Example: Psychopathy
 Psychcopaths are rare but cause
many problems.
 Most are male, manipulative,
deceitful, impulsive, charismatic,
charming, aggressive,
promiscuous, and show little guilt
for their antisocial behaviours.
 They are impatient, unable to
control their impulses and are
less affected by the
consequences of their actions
(Howard et al., 1997).
 They do not react in a normal
physiological manner to cues of
distress or to aversive stimuli
(Patrick, 1994).
Psychopathy as an Adaptation.
 Lalumière et al., (2001) point out that psychopathy has
traditionally been viewed as a brain pathology stemming
from a disturbance in the developmental process. They
provide an alternative explanation.
 The behavioural, emotional and cognitive impairments
displayed by psychopaths may represent a set of adaptive
features that would have once thrived during human
evolutionary history.
 Harpending & Sobus (1987) used game research to show
that cheaters could thrive under certain conditions:
 When they are difficult to detect.
 When they are highly mobile.
 If they are highly persuasive.
 If they are very attractive (physically or possess charisma).
Psychopathy and
Developmental Instability?
 Lalumière et al., (2001) noted
that if psychopathy is the
result of an early maladaptive
development, than
psychopaths should display
markers of developmental
perturbations.
 They assessed prevalence of
psychopathy and number of
reported obstetric problems
in 800 violent male offenders.
 Those scoring highest on the
psychopathy checklist were
less likely to have
experienced developmental
perturbations.
Psychopathy and
Developmental Instability?
 In a second study they
measured fluctuating
asymmetry in psychopathic and
non-psychopathic offenders and
a control group of nonoffenders.
 FA was indeed lower in the nonoffenders and was highest in
the non-psychopathic offenders,
the psychopathic offenders fell
in-between these groups.
 The authors argued that their
research showed some support
for the idea that psychopathy is
not caused by developmental
disorder.
Anorexia.
 Standard explanations of eating disorders revolve around
proximate
explanations,
e.g.
cultural
pressures,
neurochemical disturbances, genetic predisposition's.
 These factors are undoubtedly important yet do not
address why females suffer disproportionately from eating
disorders?
 Evolutionary explanations attempt to take a more ultimate
view to take account of the possible adaptive nature of
such behaviours and there are several models:
a) Reproductive Suppression
Hypothesis (RSH).
 Biologists have noted that female mammals are able to
suppress their reproductive capability when environmental
conditions are poor.
 In modern industrial societies adolescent females eat high
calorie foods, enter menarche much earlier, and thus spend
a longer time before marriage and children than previous
generations.
 During this time young girls may receive attention from
many males so sexual activity is difficult to avoid, and is
costly if it results in fertilisation.
 Voland & Voland (1989) suggested that anorexia nervosa is
an emergency strategy that suppresses reproduction
achieved through reducing critical fat mass below that at
which ovulation is possible.
b) Sexual Competition Model.
 Abed (1998) pointed out the following:
 Female body shape and relative thinness is (and was) an
honest marker of age and reproductive potential.
 A specific body size/shape is attractive to males and serves
as a competitive signal to other females.
 Humans have the cognitive capacity to recognise their own
mate value and act accordingly to change their appearance.
 Abed (1998) hypothesised that eating disorders are an
example of 'runaway' intra-sexual competition.
 Sexual selection would favour females who not only
possessed a nubile shape but who also possessed the
psychological adaptations that enabled them to recognise
that this attractive body shape was under threat (i.e. by
obesity or age).
Sexual Competition Model continued
 It would thus be adaptive for females to monitor their own
body size/shape and constantly compare this with
surrounding females.
 If (as in modern Western societies) women are increasingly
surrounded by images (or real-life) young, thin, nubile
females, then this would produce a drive for relative
thinness in order to improve ones mate value. This may
manifest itself in different ways:
 In younger females anorexia nervosa is an attempt to
engage in intra-sexual competition where the nubile female
shape is set at an abnormally thin level.
 Amongst
older
females,
bulimia
nervosa
should
predominate, as it is an attempt to reactivate their once
nubile shape in an attempt to maintain mate value.
Non-Pathological Outcomes.
 Natural selection would have
used powerful emotions such as
guilt, depression and anxiety to
ensure
that
a
redeeming
strategy is conducted.
 These emotions would generate
a feeling of dissatisfaction with
one's own body size and shape
and motivate the individual to
address this.
 Many women are concerned with
their weight, are on (or have
been
on)
diets,
exercise
regularly, are aware of caloriecontents of foods etc.
c) Perceived Social Rank.
 Treasure & Owen (1996) noted that sheep, goats and pigs
may all display eating disorders when healthy and where
food is plentiful.
 In these cases the disorder appears to have been triggered
by defeat in competition for social rank.
 Such defeat is accompanied by submissive behaviours in
order to avoid being attacked, where an animal cannot
escape dominating individuals this situation leads to stressrelated disease and depression.
 Human societies also characterised by social ranking in
competition for resources.
 Depression may be an evolved manifestation of submissive
behaviours when there is no opportunity to escape a
dominating situation (Gilbert, 1992).
Test of the Hypothesis.
 Troop et al., (2003) reviewed a series of studies showing
that indicators of low social rank (feelings of inadequacy,
low self-esteem, lack of control, lack of assertiveness etc)
are common in patients with eating disorders.
 They then explored perceived social comparison and
submissive behaviour in women and men with eating
disorders.
 Patients displayed significantly lower social comparison
scores and significantly higher submissiveness scores than
matched controls.
 The authors argue that patients with eating disorders do
compare themselves less favourably with others and also
report themselves to be more submissive than others in
everyday life.