MZ’ indicates identical twins with the same sets of genes and ‘DZ’ indicates fraternal twins where genes are mixed to an extent similar to that of non-twin siblings. In 2000 Bailey, Dunne and Martin studied a larger sample of 4,901 Australian twins but reported less than half the level biology exploring life pdf concordance.
Other researchers support biological causes for both men and women’s sexual orientation. Women showed a statistically non-significant trend to weaker influence of hereditary effects, while men showed no effect of shared environmental effects. Biometric modeling revealed that, in men, genetic effects explained . 39 of the variance , the shared environment .
00, and the individual-specific environment . Corresponding estimates among women were . 19 for genetic factors, . 17 for shared environmental, and . 66 for unique environmental factors. Nonetheless, it is possible to conclude that, given the difference in sexuality in so many sets of identical twins, sexual orientation cannot be attributed solely to genetic factors.