Secondary Sexual Characteristics Sexual Reproduction • Why sex? Increases variation If parents are involved in bringing up offspring, it increases the chances of offspring surviving • This is the point of all animal courtship rituals- to select the best possible male and increase participation in bringing up offspring Sex • Animals take several strategies: External fertilisation (sperm & eggs released into water). There may or may not be parental care of offspring. Internal fertilisation (sperm introduced into female). Usually parental care of offspring. • • We are going to examine human reproduction firstremember that humans are placental mammals. They also invest a lot of parental care, ensuring a high survival rate for offspring. Thus, there are complex rituals which aim at increasing bonding and involvement with offspring. Primary and Secondary Characteristics • Primary sexual characteristics – These are the organs directly involved in reproduction. – Males- penis, testes, prostate gland & other seminal glands – Females- vagina, uterus, ovaries, fallopian tubes • Secondary sexual characteristics – The physical characteristics associated with a person’s sex but not directly involved in reproduction. Differences between males & females fall into three categories: Reproductive Different physical roles Signalling differences • Secondary sexual characteristics are produced by sex hormones. • • In males, the main sex hormone is testosterone (there are other androgens). • • In females, the sex hormones are oestrogens & progesterone. • Note: both males & females produce small amounts of both hormones in the adrenal glands. • Male and Female Secondary Sexual Characteristics • Males – – – – – body size & muscular development Enlargement of the larynx (vocal cords) - deeper voice red blood cell count body & facial hair The skull is more angular- heavier lower jaw, stronger brow ridges to protect eyes – Armpit & pubic hair- these areas have different sweat glands which may produce pheromones. • Females – Breast development- breast tissue is composed of glandular tissue & fat – Widened pelvis- the pelvis becomes wider & more bowl shaped – body fat – Armpit & pubic hair • What controls the hormones producing these effects? • Answer: the brain! • 1. The hypothalamus (area of the brain) releases Gonadotrophin Releasing Hormone (GnRH). • • 2. GnRH stimulates cells in the anterior pituitary gland to release Follicle Stimulating Hormone (FSH) and Lutenising Hormone (LH) into the bloodstream. • 3. FSH & LH stimulate the gonads to produce the appropriate hormones. Questions • 1. What is the function of the increased body fat in women? • 2. Why have males evolved to have a larger body size & musculature? • 3. What are some secondary sexual characteristics in other mammals? Give at least three examples. • 4. What roles do the secondary sexual characteristics play in other mammals? Give at least two examples. • 5. Other mammals do not have breast development except for when lactating (breastfeeding). Why might humans have evolved with breast development?