Sexual preferences are based on both a genetic disposition and epigenetic imprints (environmental factors that are individual to everyone). The importance of environmental influences in the development of homosexuality is confirmed by twin studies.
The latter are largely early childhood imprints between the ages of 0 and 3 years.
The determination of the genetic or chromosomal sex (XX or XO as well as XXX or XY or XXY as well as XYY) is objective; due to this, a female or male differentiation of the gonads/gonads (ovaries/ovaries or testes/testicles) occurs approximately from the fifth week of pregnancy.
Gender identity (sex identity) in the nucleus is formed even during the first year and a half of life.
At the end of the fourth year of life, the phase of actual gender differentiation begins.
Gender identity: “a person’s subjective sense of experiencing him/herself as male or female/binary (or in-between/non-binary)” is probably primarily formed prepubertally. Little is known about the further development of gender identity in adolescence, although a large social component can probably be assumed.
Disturbances in the metabolism of hormones (pituitary-gonadal axis) and neurotransmitters (dopamine, serotonin) are also considered possible causes.
