Understanding Twins (original) (raw)

The special relationship between twins allows researchers to examine the differences between genetic and environmental influences over both physical and mental health, as well as traits and behaviors. By studying twins, we can learn a lot about diseases, disorders, and human nature in general. Research on twins helps answer questions about many aspects of being human. About three or four in every 1000 births are identical twins.

There are different types of twins, identical and fraternal being the most common. Identical, or monozygotic, twins develop from the same fertilized egg that splits into two. These twins are of the same sex and share the same genes. Sometimes called paternal twins, identical twins provide evidence of a high degree of genetic influence on human development. For fraternal or dizygotic twins, they develop from two different eggs fertilized by separate sperm; they generally share about half of their genes. Therefore, fraternal twins are essentially like typical brothers and sisters.

For more on identicals and fraternals, visit Identical Twins and Fraternal Twins.