It was concluded, among many other things, that identical twins are about 85 percent similar for IQ, whereas fraternal twins are about 60 percent similar. This would seem to indicate that half of the variation in intelligence is due to genes.
The only significant difference found was at age 10. Using the family-based adult sample, no differences in IQ scores were found between twins and their singleton siblings.
However, the intelligence test showed a surprising difference in IQ levels, with the sister raised in the US 16 points lower than her sibling – ten points greater than the documented average gulf between identical twins raised together. There were also marked differences in non-verbal reasoning scores.
Identical twins have more similar IQ scores than fraternal twins and adopted children have IQ scores that relate more closely to their biological parents than adoptive parents. This provides evidence for a genetic component to intelligence.
Studies show that the correlations of IQ scores for identical twins reared together and for identical twins reared apart are both strong (. 86 and . 76, respectively).
But enough studies have been done to show that identical twins are roughly 85 percent similar for IQ, fraternal twins about 60 percent. Crunching the numbers, behavior geneticists say about half the variation in IQ, whether among twins or non-twins, may be due to genes.
The mean correlation of IQ scores between monozygotic twins was 0.86, between siblings 0.47, between half-siblings 0.31, and between cousins 0.15.
The mean absolute difference between twins is 6.60 (SD = 5.20), the largest difference being 24 IQ points. The frequency of large twin differences is no more than would be expected from the normal probability curve.
In this investigation, researchers found that identical twins raised together and identical twins raised apart exhibit a higher correlation between their IQ scores than siblings or fraternal twins raised together (Bouchard, Lykken, McGue, Segal, & Tellegen, 1990).
The University of Edinburgh study reported that the oldest child tends to have a higher IQ and thinking skills than their younger siblings. This is due to higher mental stimulation the first-born receives, CBS affiliate KUTV reports.
Thus identical twins, though they start with the same genes, likely develop different personalities in the same environment partially based on how they interact with their environment.
Previous studies show that schizophrenia affects both members of identical twins in 41% to 61% of cases, but only 0 to 28% in non-identical twins. A previous pooling of twin studies has suggested that the "heritability" of schizophrenia is 81%.
But genetics can explain the wide range of possible IQs too because so many different genes are involved in developing and running a brain. It is possible, for example, to inherit all the higher IQ genes from each parent and leave the lower IQ ones behind. Now the child will be brighter than the parent.
Although this is a robust and statistically significant finding the IQ difference is small. It means that in six out of ten cases the older sibling will have a higher IQ than the next youngest sibling.
“Twin studies of major depressive disorder have showed that if one twin has the illness, a fraternal twin has an increased likelihood of developing the disorder and an identical twin's likelihood is even higher,” says Dr. Avari.
Like, is Elon Musk a genius? It answered, Elon Musk's IQ is reported to be 155, which is very high compared to the average of 100.
There are several successful entrepreneurs who are known for their high IQ scores, such as: Jeff Bezos: The founder of Amazon, Bezos has an IQ estimated to be around 145.
2 Lady Gaga's IQ Is 166
One thing that many may not know is that gaga actually has an impressively high IQ of 166 which means that she falls into the exceptionally gifted category — just like Ashton Kutcher, Quentin Tarantino, and Matt Damon.
Like most aspects of human behavior and cognition, intelligence is a complex trait that is influenced by both genetic and environmental factors.
They come from the same fertilized egg and share the same genetic blueprint. To a standard DNA test, they are indistinguishable. But any forensics expert will tell you that there is at least one surefire way to tell them apart: identical twins do not have matching fingerprints.
Since identical twins share the same DNA, the children of two pairs of identical twins are legally cousins, but genetically more similar to siblings.
In this investigation, researchers found that identical twins raised together and identical twins raised apart exhibit a higher correlation between their IQ scores than siblings or fraternal twins raised together (Bouchard, Lykken, McGue, Segal, & Tellegen, 1990).
Intelligence Beyond the General Abilities
Intelligence is more than those general abilities, which is why intelligence and IQ aren't the same. Since our immediate environment can include other people, we need to be able to understand them.
Which pair of family members is likely to have the most similar IQ scores? Identical twins.