1. Sources of human psychological
differences: the Minnesota study of twins
reared apart.
Thomas J. Bouchard Jr.; David T. Lykken; Matthew McGue; Nancy L. Segal; Auke
Tellegen Science, Oct 12, 1990 v250 n4978 p223(6)
http://www.nature.com/nrg/journal/v2/n5/full/nrg0501_326a.html
Monozygotic and dizygotic twins who were separated early in life and reared apart (MZA
and DZA twin pairs) are a fascinating experiment of nature. They also provide the
simplest and most powerful method for disentangling the influence of environmental and
genetic factors on human characteristics. The rarity of twins reared apart explains why
only three previous studies of modest scope are available in the literature [1-4].
Before comparing twins reared separately and twins reared apart, psychologists
determined if twins were monzygotic (split from ONE EGG) or dizygotic (TWO
SEPARATE EGGS FERTALIZED).
http://www.psych.umn.edu/psylabs/mtfs/mtrf1.htm
Table 1 - Questions used for zygosity diagnosis*
A. Your eye color:
Same color (1) Similar, different shade (0) Different color (-5)
B. Your (natural) hair color:
Same color (1) Similar, different shade (0) Different color (-5)
C. (Even identical twins sometimes differ quite a bit in height or weight as a result of accident or
illness. In answering the questions below, try to ignore such differences.)
1. During your childhood, were you and your twin as alike as "two peas" or were you no
more alike in appearance than ordinary brothers or sisters?

Like "two peas" (3) Ordinary likeness (0) Quite unlike (-3)
2.When you were school age, were you similar enough in appearance so that people had
difficulty telling you apart?
 Never (-2) Sometimes (2) Even family had difficulty (3)
3. Could you ever have fooled friends or family by pretending to be your twin?
 Yes (2) Maybe (0) No (-1)
*Weights assigned to each alternative answer are shown in parentheses. These weights
were assigned rationally (eg, different eye or hair color ensures dizygosity; general
physical similarity gets more weight than similarity on one trait) and the cutting score
chosen inspection of the bimodal distribution for the total same-sex sample. Twins are
classified as monozygotic if the sum of the weighted responses is +4 or higher.
More than 100 sets of reared-apart twins or triplets from across the United States and the
United Kingdom have participated in the Minnesota Study of Twins Reared Apart since it
began in 1979. Participants have also come from Australia, Canada, China, New Zealand,
Sweden, and West Germany. The study of these reared-apart twins has led to two general
and seemingly remarkable conclusions concerning the sources of the psychological
differences - behavioral variation - between people: (i) generic factors exert a pronounced
and pervasive influence on behavioral variability, and (ii) the effect of being reared in the
same home is negligible [insignificant] for many psychological traits. These conclusions
will not come as revelations to the many behavioral geneticists who have observed
similar results and drawn similar conclusions [5]. This study and the broader behavioral
genetic literature, nevertheless, challenge prevailing psychological theories on the origins
of individual differences in ability, personality, interests, and social attitudes [6].
First twins studied were identical twins Jim Lewis and Jim Springer who were only four
weeks old when they were separated; each infant was taken in by a different adoptive
family. These twin siblings, separated at birth, had the same name, were both 6 feet tall
and weighed exactly 180 pounds. But there's more.


As youngsters, each Jim had a dog named "Toy."
Each Jim had been married two times -- the first wives were both called
"Linda" and the second wives were both called "Betty."
 One Jim had named his son "James Allan" and the other Jim had named
his son "James Alan."
 Each twin had driven his light-blue Chevrolet to Pas Grille beach in
Florida for family vacations.
 Both Jims had at one time held part-time posts as sheriffs.
 Both Jims were interested in woodworking and had circular white
benches around a tree in each of their front yards!
 Both were fingernail biters and suffered from migraine headaches.
 Each Jim enjoyed leaving love notes to his wife throughout the house.
Of course, before you start thinking about science fiction movies with pod people, the
Jims, like other identical twins, are not carbon copies of each other. Some obvious
differences were discovered during their participation in the "Minnesota Study of Twins
Reared Apart," including:
 Each styled his hair differently; one Jim wore it combed straight,
hanging down over his forehead (think Beatles circa 1961) and the other
Jim wore it combed back and sported sideburns (think Johnny Cash
circa 1957, but with longer 'burns).
 One Jim more clearly conveyed himself through speech, while the other
was better suited to writing.
 While both Jims had been married twice, one Jim had taken vows with a
third wife (called "Sandy")
http://science.howstuffworks.com/twin1.htm
2. Human genetics: I got rhythm, I got music
Magdalena Skipper
http://www.nature.com/nrg/journal/v2/n5/full/nrg0501_326a.html
Last year, Simiak Baharloo and colleagues showed that absolute pitch — the ability to
identify precisely and rapidly the pitch of a note — has a substantial genetic component
(see Highlights, October 2000). Now, Dennis Drayna and colleagues focus on relative
pitch (RP) — the ability to perceive pitch alterations — and find that it also has a
surprisingly large genetic component.
To investigate the relative contributions of genetics and the environment to RP
perception, Drayna et al. used a twin study and a modernized distorted tunes test (DTT)...
They tested 136 monozygotic (MZ) and 148 dizygotic (DZ) Caucasian female twins for
their ability to spot false notes in popular tunes. Statistical analysis of the results revealed
a significant difference in the DTT scores between MZ and DZ twins, which indicates a
strong genetic component to RP perception.
The correlation of DTT scores for the MZ data set was calculated at 0.67 compared with
0.44 for the DZ data set. But the authors point out that the results will need to be
replicated in other populations.
By showing that RP perception might be partly 'hardwired', this study has struck a chord
among cognitive scientists who are
studying communication disorders,
and who noticed a long time ago
that musicality and language
ability go together. They might
now be encouraged to look for the
genetic basis of such disorders.
3. Do Identical Twins Have
Identical Politics?
Now that the president of Poland has died in a
plane crash, his twin brother may run for the job.
Will his platform be the same?
By Brian PalmerPosted Wednesday, April 21, 2010, at 4:53 PM ET SLATE MAGAZINE
Members of Lech Kazcynski's family, including his twin brother, Jaroslaw Polish voters will
head to the polls on June 20 to elect a replacement for the late President Lech Kaczynski,
who died in a plane crash two weeks ago. Kaczynski's identical twin brother, Jaroslaw, may
contest the election. Are Jaroslaw and Lech any more likely to agree with each other on
political matters than George and Jeb Bush or Jack and Teddy Kennedy?
Yes, but no one really knows why. In recent years, researchers have posed a series of hotbutton political questions to pairs of identical and fraternal twins. The first major study of this
kind, published in 2005, asked twins for their positions on issues like foreign aid, death
penalty, and abortion. Survey responses from identical twins were more correlated than those
from fraternal twins on every issue. That is, the more genetic similarity, the more political
similarities. School prayer and property taxes were singled out by the researchers as being
the most strongly influenced by genetics. When responses were aggregated and reduced to
either a conservative or liberal worldview, the authors concluded that genetics could explain
43 percent of someone's political outlook.
While most observers agree that identical twins are more likely to share a political identity,
many have contested the notion that genetics are the cause. Studies of this kind are based on
the assumption that monozygotic (identical) twins share the same genes and the same
environment, while dizygotic (fraternal) twins have only the latter in common. But identical
twins are not always treated the same way as dizygotic twins. They may be dressed the same
way by their parents, made to sleep in the same bedroom, or given rhyming names. They're
also likely to spend more time together and to be confused for each other by family and
friends. At the same time, monozygotic twins aren't really genetically identical (epigenetics)
in the first place. So their convergent worldviews might be due to environmental, and not
genetic, factors.