In the womb, a fetus with XY chromosomes is exposed to testosterone and other androgens that help it develop into a male. Research has shown that people exhibit features that give away how much testosterone we were exposed to before birth. The digit ratio is the ratio between the length of the second and fourth fingers. If both fingers are the same length, the ratio is 1. The lower the digit ratio (ring finger longer than index finger), the more testosterone the fetus was likely exposed to.
It is not clear why testosterone affects the length of your fingers, but there is significant evidence to support the theory. Men with a lower digit ratio tend to be described as more aggressive, dominant and overall “masculine”. Men with a higher digit ratio, closer to 1, are typically described to have more feminine traits such as higher emotional quotient, sensitivity and interestingly, excelling in mathematics and science. The effect is more pronounced in men but also affects women. Women with a low digit ratio are more likely to be assertive. It has also been shown that lesbian women have a lower digit ratio than heterosexual women.
It is often believed that for complex organisms such as animals, sexual reproduction is a must to produce offspring. Asexual reproduction is common in bacteria and (some) plants, but even tiny beings such as insects use sexual reproduction to produce a mass of variable offspring.
However, it has been found that despite having two clear sexes – male and female – there are cases where a certain species is able to reproduce without the need of sexual intercourse. In these cases, the female’s eggs spontaneously divides to form a new offspring without being fertilised by a sperm. Furthermore, sometimes the egg either fuses with another egg or undergo several genetic mixing and mutation to produce some variety in genetic pool, thus avoiding the issue of asexual reproduction (where the entire population can be wiped out by a single disease due to identical genetic makeup). This is known as parthenogenesis, and it has been documented in many insects, fish, reptiles and even birds.
Obviously, as there is no donation of a Y chromosome, every offspring born from parthenogenesis is female. Because of this, some species such as the New Mexico whiptail, a lizard that is capable of both sexual reproduction and parthenogenesis, the population has completely rid itself of males, making it a completely female species. Curiously, they still engage in “mock sex”, giving them the nickname “lesbian lizards”.
Although parthenogenesis has never been documented in mammals in nature, it has been induced artificially in mice, rabbits and monkeys. However, they all developed severe developmental issues due to the numerous mutations in the egg required for parthenogenesis.
But if in the future, human parthenogenesis is perfected, it is possible that humanity too could end up as an all-female society.