A psychological study of the personalities of XYY- and XXY-men
In 1965, a comparison of data from four surveys which included "...ordinary..." youth who were "..mentally backward..." (Maclean et al, 1962), newborns (Maclean et al, 1964), and patients at the Rampton and Moss Side British State Hospitals (Casey et al, published in 1966), revealed a low incidence of 48,XXYY males among the "ordinary" and newborn population and a high incidence of 48,XXYY among males institutionalized in the state hospitals because of anti-social behavior. This data suggested that individuals with an extra Y chromosome might be predisposed to anti-social behavior. In a study designed to test this hypothesis, Jacobs et al (1965) initiated the first chromosome survey for XYY males among an institutionalized population described as "...dangerous, violent and criminal..." This study demonstrated a significantly higher incidence of men with an extra Y chromosome (3.5%) in this population than might be expected at birth supporting a possible association between the XYY chromosome complement and anti-social behaviors.
they are inclined to show less aggression against …
If such variationexists, then in any population the correlation between the XYY karyotypeand aggression would depend on the distribution of Y chromosomes havingvarying degrees of predisposition towards aggressive behaviour.
Include notes on the following:
-limbic system, including amygdala
-chemicals/hormones (testosterone, serotonin
-chromosome abnormalities (XYY syndrome)
Biological Explanation of Aggression
Limbic System (part of the Central Nervous System):
-linked to aggression
-damage to the limbic system ncreases aggression, and decreases fear
but, damage to the
(part of the limbic system) results in timidity
Deliberate surgical damage to parts of the brain
psychosurgery to the amygdala has reduced violent behaviour in patients
but it can also affect other functions, like a person's ability to read emotional cues (facial expressions or tone of voice)
Some people think we can be born with the tendency to be aggressive
A chromosome is a long, thin strand of DNA found in our cells that carries all of the genetic material that makes us who we are.
Pervasive aggression in an XYY karyotype
Meanwhile, case reports which addressed developmental issues in XYY children, described them as "...enigmatic in their personality development...vulnerable to simple threats and stresses that most would shrug off...loners...aggressive with fits of temper ...(who) plan their activities on an isolationist basis, so that one cannot quite predict what might develop tomorrow or next week..." (Money, 1970). In a study of five XYY children- Zeuthen et al (1975) said: "...it was characteristic that all five males with XYY who grew up in good homes, to a certain extent differed from their ...siblings..." in that they were "...more impulsive, restless, hot tempered, hyperactive ...and lacked control of aggressive impulses..."
Treatment of pervasive aggression in a patient with 47 XYY karyotype
The XYY hypothesis is an example of
, suggesting aggressive behaviour is controlled by physiological factors.