Patricia Jacobs did a study of inmates of a Scottish
prison and published her findings in Nature in 1965. She found that 4%
of prisoners had 2 Y chromosomes instead of the more normal XY pairing
found in males. In the general population, about 1 in 1,000 were
thought to have this abnormality; so a much higher proportion of double
Y chromosome individuals were in prison than might be expected.
This study was hailed at the time as having found a basic cause of
criminality and aggression and the double Y chromosome possessors were
identified as having Jacob's Syndrome.
Newer research has shown that in general males with 2 Y
chromosomes are found to be taller and prone to acne, they often have
difficulty with reading and speech but are generally not otherwise
notably different to others. Their higher proportion in prison
populations could be simply that they are more likely than others to be
caught and convicted, at least partly due to verbal difficulty. However
it should be noted that 96 % of men with Jacobs Syndrome are quite
normal law-abiding citizens.
Sujeeva has posted information on this site to the effect that
"80% of those arrested for crime and 90% of those arrested for violent
crime have an extra Y chromosome " This seems improbably high in view
of their low incidence in our population -- I query her statistical
accuracy here. Others place them as 20times more likely to be
imprisoned, but since they are about 0,1% of the total population, this
is still quite a low number.
In 1980 a study found increased incidence of double Y
chromosomes in the sperm of men exposed to Chemo and Radiation
treatment, to X-rays , and to dibromochloropropane; suggested screening
for the condition during pregnancy.