These explanations may sound ludicrous however, as of now these are the only answers we know of because scientists are still in the process of looking for the answer to why monogyzotic twins occur. On the other hand, we do know more about dizygotic twins and their causes. Dizygotic twins may occur for several different reasons for example, ethnic origin, age of mother, levels of Gonadotroghin hormone, diet, heredity, and infertility treatments. Ethnic origin strongly effects the chances of having twins.
Black women have the highest rate of twinning in the United States.
In between the African Americans and the Chinese fall, from greatest probability to least, the American Indians, Japanese, Hawaiians, and the Filipinos. Women who have dizygotic twins have higher levels of gonadotroghin. Gonadotroghin is a hormone produced by the pituitary gland which stimulates the ovaries to mature and release their eggs into the fallopian tube. With race, age, and gonadotroghin, diet and vitamin intake are other elements to take into consideration. Yams are said to contain hormone like substances that have an effect on a mothers fertility.