Biological Influences on sex and gender

• Biological influences on gender are the nature side of the nature/nurture debate.
• To sum up, glands involved in sexual reproduction are called sex glands.

  Males have testes whereas females have ovaries .
• Chromosomes are made of tightly-wound DNA and are found in all cells.
• Sex cells (sperm and eggs) each have 23 chromosomes. All other cells in the body have 23 pairs of chromosomes.
• The final pair of chromosomes control our biological sex, meaning whether we are born with male bodies or female bodies.
• Sex chromosomes are...

  • the 23rd pair of chromosomes
  • present in all the cells in our body
  • what controls our biological sex
• People who are biologically female have exactly two X chromosomes.

  People who are biologically male have exactly one X chromosome and one Y chromosome.
• The Y chromosome contains the SRY gene, which causes sex glands to develop into testes. Therefore If a person has XY chromosomes, their sex glands develop into testes. (e.g. males)
• Since females have ovaries, they produce oestrogen.

  Since males have testes, they produce testosterone .
• The testes produce testosterone,  meaning males produce a larger amount of testosterone, causing male genitalia such as the penis to develop.

  The ovaries produce oestrogen, meaning females produce a larger amount of oestrogen, causing female genitalia such as the vagina to develop.
• Testosterone and oestrogen are also released by non-sex glands, such as adrenal glands.
• To sum up, hormones control puberty , during which...

  Testosterone causes males grow taller , have deeper voices, and pubic hair.

  Oestrogen causes females to develop breasts, have periods, and also grow taller.
• What is Oxytocin?

  • Oxytocin is a hormone
  • Oxytocin is produced by the pituitary gland.
  • Females produce more oxytocin than males.
  • Oxytocin helps females give birth by stimulating the muscles around the uterus.
  • Oxytocin stimulates the production of milk from a woman’s breasts.
• Oxytocin is associated with empathetic, sensitive and caring behaviour.

  Females produce more oxytocin than males.

  Females are often seen as more empathetic, sensitive or caring than males.

  So oxytocin may influence behavioural differences, or in other words: oxytocin may influence gender .
• Testosterone may explain gender differences in aggression and competitiveness. Evidence for this comes from studies which have shown positive correlation between testosterone levels and aggression/competitiveness.
• (Sexually dimorphic nucleus) The size of this region of our brain was influenced by the level of testosterone in our bodies when we were babies. So this region the hypothalamus is much larger in males.
• Testosterone may influence brain development in two ways:

  • Firstly, testosterone increases the size of the sexually dimorphic nucleus in the hypothalamus , a brain region that controls sexual behaviour.
  • Secondly, testosterone may increase brain lateralisation , which might cause differences between how males and females behave.
• Support for the Effect of Testosterone on Gender


  Study's that found children exposed to testosterone before they were born tend to display more masculine behavioural characteristics.
• Limitations of Hormone Studies

  Firstly, some of the studies are correlational and can’t therefore establish cause and effect relationships.

  Secondly, many studies are animal studies which may not generalise to humans.
• One limitation of hormone studies which directly investigate cause and effect in humans.

  Expectations about the effects of hormones can act as confounding variables.

  For example, when Eisenegger deceived women by telling them they were taking testosterone , they behaved more competitively and unfairly.
• Limitations of Brain Imaging Studies

  Firstly, these differences are not always replicated by other studies. For example, a meta-analysis undertaken by Janet Hyde found very little difference between the brains of males and females.

  
  

  Secondly, other studies have found bigger differences within the sexes than between them.
• Support for Biological Influences - David Reimer Case Study

  David Reimer was born biologically male but underwent a sex change in which his genitalia were removed. His parents tried to raise him as a girl but failed, which suggests that gender is greatly influenced by biological factors like having XY chromosomes and high testosterone levels before birth.
• An intersex condition is when a person doesn’t develop the genitalia typical for their sex chromosomes.
• An abnormal chromosome pattern is when a person has more or less than 46 chromosomes.
• An atypical sex chromosome pattern is when a person has more or less than 2 sex chromosomes. e.g. XXY or X
• Klinefelter's syndrome


  Affects: Boys

  Chromosome pattern: XXY

  Symptoms (physical): Less muscly, less hairy, taller, infertility, breast tissue development.

  Symptoms (psychological): Language and reading difficulties

  Frequency: 1 in 1000
• Turners syndrome


  Affects: Girls

  Chromosome pattern: X

  Symptoms (physical): Shorter, webbed neck, infertility, underdeveloped ovaries, not getting periods.

  Symptoms (psychological): Above average verbal ability, bellow average maths ability, difficulties making friends.

  Frequency: 1 in 2000