If two twins in an identical pair tend to have closer IQ's than two twins in a fraternal pair, then genes probably play a role in IQ. Identical twins are definitely more likely to share the same IQ than are fraternal twins. So genes do play a role in IQ.
Criticisms of fundamental assumptionsCritics of twin studies argue that they are based on false or questionable assumptions, including that monozygotic twins share 100% of their genes and the equal environments assumption.
Dizygotic (DZ) or fraternal twins (also referred to as "non-identical twins", "dissimilar twins", "biovular twins", and, informally in the case of females, "sororal twins") usually occur when two fertilized eggs are implanted in the uterus wall at the same time.
What was the primary finding of the Minnesota Study of Twins Reared Apart? Identical twins, whether raised together or apart, have very similar personalities.
What have twin studies revealed about intelligence? Intelligence is partly influenced by heredity. A psychologist is developing a theoretical explanation about a behavior.
Which factor best describes the Flynn Effect? Average IQ scores in the United States have risen dramatically over the past decades. Some children show a lowering of their IQ during their school years.
The studies of reared-apart twins have shown that in general, half the differences in personality and religiosity are genetically determined, but for a trait like I.Q., about 75 percent of the variation, on average, is genetic, with only 25 percent influenced by the environment.
The research team found that identical twins who are reared apart had the same chance of being similar as twins who were raised together. Bouchard and his colleagues concluded that genetic factors have a large influence on behavioral habits demonstrating the influence of the genetics on development.
Twins are Never “Separated at Birth”Keeping two (or more) siblings together is a choice made in the best interest of all involved, especially the children at the center of the adoption.
Both studies confirm that greater similarity of treatment does not make MZ twins are more similar. b. Separated twin studies and standard twin studies give very similar results. Critics are quick to point out that many twins in separated twin studies were not totally separated.
The traditional way of studying nature versus nurture relies on twins. Because identical twins share the same genetic code, comparing the health of twins can help determine whether genetic or environmental factors play more of a role in their health.
Researchers can isolate genetic traits and study only the influence of environmental factors on individual development. 2. Researchers can study whether genetics or the environment plays a stronger role in shaping individual behavior.
Similarly, drugs, chemicals, temperature, and light are among the external environmental factors that can determine which genes are turned on and off, thereby influencing the way an organism develops and functions.
Twin studies used to be almost the only way to compare the influence of genes against the environment on personality and behavior. Recent advances in genetics, however, suggest that opposing “nature” to “nurture” is misleading. Genes combine with the environment to produce complex human traits.
What was the advantage of the MISTRA over other studies of twins? The twins had grown up in different environments.
Identical twins came from the same sperm and egg, so they have the same chromosomes and genes. But there are environmental differences that can affect the way they look and behave. As identical twins get older they may look more and more different, because they are exposed to more diverse environments.
Twins provide a valuable source of information for health and psychological research, as their unique relationship allows researchers to pull apart and examine genetic and environmental influences. Twin studies allow researchers to examine the overall role of genes in the development of a trait or disorder.
Identical twins are also known as monozygotic twins. They result from the fertilization of a single egg that splits in two. Identical twins share all of their genes and are always of the same sex. In contrast, fraternal, or dizygotic, twins result from the fertilization of two separate eggs during the same pregnancy.
If you want to know whether the personality traits extraversion and agreeableness run in our genes, you need to measure relevant thoughts, feelings, and actions.
In 1979, a scientist named Thomas Bouchard set out to study the similarities and differences between twins—both identical and fraternal—who were separated within the first 6 months of their lives and raised apart from each other.
Oskar Stohr and Jack Yufe were identical twins, separated shortly after birth. Oskar was raised as a Catholic and a Nazi. Jack grew up as a Jew. These were two men with the exact same genes–they shared the same egg in their mother's womb, and they now shared the same DNA.
David Buss, an evolutionary theorist, has attributed the Big Five personality traits to evolved ancestral needs.
Personality traits are complex and research suggests that our traits are shaped by both inheritance and environmental factors.
James 'Jim' Springer, of Piqua Ohio, was adopted in 1940 just three weeks after he was born. In 1979, Jim Lewis met Jim Springer, and the truth behind their startling similarities came out. They were twins, separated at birth, who had grown up not 45 miles from each other, and ended up leading almost identical lives.
Why do researchers use adoption studies in an effort to reveal genetic influences on personality? To evaluate whether adopted children more closely resemble their adoptive parents or their biological parents.
Bouchard worked on twin study, particularly as part of the Minnesota Study of Twins Reared Apart (MISTRA). This work has included case studies, longitudinal studies, and large-scale quantitative analyses and meta-analyses.
