Additional info:

The scientists behind Sex ID asked test takers a series of questions, some of which covered personal or sexual topics. The questions were included to help researchers learn more about brain sex differences. For example, they are interested to know how test takers' finger measurements relate to the number of brothers and sisters they have. There is a theory that the amount of testosterone we are exposed to in our mothers' wombs relates to the ratio of the length of our index fingers to the length of our ring fingers – our digit ratios. Furthermore, it's thought that prenatal testosterone may increase or decrease systematically with each male child a woman has. Dr John Manning is particularly interested to learn if there is a link between testosterone and birth order. That's why we asked test takers to measure their fingers and answer questions about their families.