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Conducted from 1979 to 1999, the Minnesota Study of Twins Reared Apart is a landmark study in behavioral genetics that examined the genetic basis of personality. By studying 350 pairs of identical and fraternal twins who were raised both together and apart, researchers discovered that identical twins exhibit very similar personalities, regardless of their upbringing. This finding provides strong evidence for the heritability of certain personality traits and is central to discussions on genetic influences on personality.

The Minnesota Study of Twins Reared Apart

Research indicates a positive relationship between genetic relatedness and intelligence quotient (IQ) scores, demonstrating that as individuals share a greater proportion of genes, the correlation between their IQ scores increases. For individuals who share no genes, such as adoptive parent-child pairs, adoptive siblings, or unrelated children raised together, the IQ correlation ranges from roughly 21 percent to 32 percent. This correlation rises to approximately 33 percent for half-siblings, who share 25 percent of their genes. For those sharing 50 percent of their genes, including parent-child pairs and fraternal twins raised together, the correlation increases to about 44 percent and 62 percent, respectively. The strongest relationship is observed in identical twins, who share 100 percent of their genes, exhibiting an IQ correlation of nearly 80 percent, even when raised apart.

IQ Correlation and Genetic Relatedness

The Minnesota Study of Twins Reared Apart identified several personality traits with a heritability ratio greater than 0.50, indicating a significant genetic influence. These traits include leadership, obedience to authority, a sense of well-being, alienation, resistance to stress, and fearfulness.

Heritable Personality Traits Identified in Twin Studies

The Minnesota Study of Twins Reared Apart provided evidence for a genetic component to intelligence. The investigation revealed that identical twins, whether raised together or apart, exhibit a higher correlation between their IQ scores than siblings or fraternal twins who are raised together.

Minnesota Study of Twins Reared Apart: Intelligence Findings

A large-scale study tracks pairs of siblings and measures the similarity of their intelligence scores, expressed as a correlation coefficient (where a higher value means more similarity). The results for three distinct groups are summarized below:

| Group | IQ Score Correlation |
| :--- | :--- |
| Identical Twins (reared in separate homes) | 0.76 |
| Fraternal Twins (reared in the same home) | 0.58 |
| Adopted Siblings (reared in the same home) | 0.29 |

Based *only* on the data in this table, 

Group	IQ Score Correlation
Identical Twins (reared in separate homes)	0.76
Fraternal Twins (reared in the same home)	0.58
Adopted Siblings (reared in the same home)	0.29

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