Do Identical Twins Think Alike?

Have you ever wondered what the world would be like if Mary-Kate and Ashley Olsen were actually identical twins? Are identical twins more similar to each other in intelligence than fraternal twins due to their genetic makeup? Before we delve into this further, we should define what are identical and fraternal twins first.

Identical twins, also scientifically referred to as monozygotic twins, occur when 2 offspring are developed from one single egg.

Fraternal twins, also scientifically referred to as dizygotic twins, are 2 offspring that are developed from 2 separate eggs.

Some very useful research techniques developed by psychologists, employed the use of twin studies and adoption studies to a have a better understanding of genes and heritability. With twin studies, psychologists were able to compare intelligence differences between monozygotic twins and dizygotic twins. Their findings revealed that monozygotic twins are more similar in intelligence (correlation of 0.86) than dizygotic twins (correlation of 0.60). Furthermore, by looking at the adoption studies, we see that monozygotic twins remain alike whether they are raised together (correlation of 0.86) or raised apart (correlation of 0.78). With this data, we can make an argument that genetics has a greater influence in the intelligence of identical twins than the environment.