The biology of sexual orientation has been one of the most vexing — and politically charged — questions in human genetics. For the first time, researchers have found associations between homosexuality and markers attached to DNA that can be influenced by environmental factors.

Researchers looked at epigenetic markers — chemical changes to DNA that affect how genes are expressed, but not the information they contain. These 'epi-marks' can be inherited, but can also be altered by environmental factors such as smoking, and are not always shared by identical twins.

However, several researchers have criticized the study’s methods and some statisticians have said that the study incorrectly presented its results as statistically significant. Study co-author Tuck Ngun has disputed this and other statistical criticisms. He has said he and his collaborators will issue a statement. Read More via Nature