Identical twins begin as a single fertilized egg, which then separates, creating two genetically similar human beings. In contrast, fraternal twins begin as two single fertilized eggs, which means that they share about 50 percent of their genetic make up, with the other 50 percent being unique to each twin. According to a 1981 study of many twins conducted by Thomas Bouchard & Matt Mcgue, it was found that identical twins raised in the same home had a correlation of a .86 IQ. On the other hand, identical twins raised in different homes had a correlation of a .72 IQ. This indicates that identical twins raised in different environments still tend to have similar IQ’s. Furthermore, fraternal twins raised in the same home had a correlation of .60. Even identical twins that don’t share the same environment have more similar IQ's than fraternal twins that do share the same environment together. If identical twins have more similar IQ scores than fraternal twins, it can be said that heredity influences intelligence (Neuroscience of …show more content…
Various factors include education, the Flynn effect, and adoption studies. Education is a very important factor. The act of simply attending school can increase one’s IQ. However, children’s IQ scores decline slightly over the course of the summer months, when children are not attending school. Children who drop out have lower IQ scores than children who remain in school, losing an average of almost 2 IQ points for every year of high school not completed. Also, one correlational adoption study produced results providing an estimate of the extent to which environmental differences influence intelligence. In comparing adopted children’s intelligence to both their adoptive parents and adoptive siblings, it was found that the children had a significantly higher correlation with their adoptive siblings (.39 with their siblings as opposed to .19 with their parents). This similarity can be explained by the similar environment the children are raised in. Furthermore, the Flynn effect describes a phenomenon which indicated that IQ has increased about three points per decade over the last 50 years, with children scoring higher than parents in each generation. This increase has been linked to multiple environmental factors, including better nutrition, increased schooling, less childhood disease, lower birth rates, and more complex environment stimulation