Sexual Reproduction

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•  William Harvey’s investigation of sexual reproduction in deer

Historical Perspective of Sexual Reproduction

One of the earliest theories as to how animals reproduce sexually was the 'soil and seed' theory proposed by Aristotle

  • According to this theory, the male produces a ‘seed' which forms an ‘egg' when mixed with menstrual blood (the ‘soil’)
  • The ‘egg’ then develops into a fetus inside the mother according to the information contained within the male 'seed’ alone

Debunking the ’Soil and Seed’ Theory 

The ‘soil and seed’ theory was a popular doctrine for hundreds of years before it was eventually debunked by William Harvey

  • William Harvey studied the sexual organs of female deer after mating in an effort to identify the developing embryo
  • He was unable to detect a growing embryo until approximately 6 – 7 weeks after mating had occurred
  • He concluded that Aristotle’s theory was incorrect and that menstrual blood did not contribute to the development of a fetus
  • Harvey was unable to identify the correct mechanism of sexual reproduction and incorrectly asserted that the fetus did not develop from a mixture of male and female ‘seeds’

Contrasting Theories of Sexual Reproduction

soil and seed theory

Modern Theory of Sexual Reproduction

Our current understanding of the mechanism of sexual reproduction is based on evidence discovered using light microscopes

  • Viable microscopes for such investigations were not invented until 17 years after the death of William Harvey

Based on available evidence, it is now known that a fetus forms from a combination of both male and females ‘seeds’ (gametes)

Modern Understanding of Gametogenesis

random fertilisation