When fertilisation occurs, the ovum contributes an X chromosome, the sperm may contribute either X (fetus will become female - XX) or Y (fetus will become male - XY)
At 8 weeks the Y chromosome carries the SRY gene, which develops testes, which produce androgens which cause secondary sex differences
Hormones
Pre-natal effects - development of sex organs, changes to neurological structure
Puberty effects - secondary sex characteristics, gendered behaviour (increased libido in males, menstruation in females)
Testosterone
10 times more in males
Linked to higher levels of aggression
Causes masculinisation of the brain - larger sexually dimorphic nucleus (2.5x larger)
Surge of testosterone during puberty responsible for secondary characteristics
Oestrogen
Female sex hormone - higher concentration in females
Regulation of menstrual cycle and development of secondary sexual characteristics
Higher levels after giving birth - maternal caregiving behaviour and reduction in oestrogen levels implicated in feelings of irritability
Oxytocin
Higher quantity in females, but same amount in both sexes during intercourse
Stimulates lactation in females and reduces effect of stress hormone cortisol
Caring-attachment behaviour in females, pair bonding behaviour in both sexes
Dampens fight or flight and stimulates 'tend and befriend'
