Reproduction: Background (DP IB Biology: SL)

• William Harvey (1578 - 1657) was an English physician who contributed greatly to our understanding of anatomy and physiology
• He is mainly remembered for his work on the circulation of the blood, however, he also spent a lot of time studying how life passes from one generation to the next and conducted much research into sexual reproduction
• At the start of the 17th century there was very little understanding of how each sex; males and females, contributed to producing offspring
  • The main hypothesis at the time was that the semen produced by males combined with the menstrual blood of females to form an 'egg', which would then develop into a foetus inside the mother

• William Harvey's work on understanding sexual reproduction involved testing this old hypothesis using animals, mainly deer
• His work included:
  • Dissecting the uteruses, or wombs, of female deer at all stages of pregnancy
    • Harvey found that the uterus was always empty at the time of conception i.e. just after successful mating, disproving the hypothesis that semen and menstrual blood combined in the uterus to form a foetus
    • Harvey expected to find 'eggs' developing in the uterus immediately after mating; instead, he only found something developing there two or more months after mating

  • Dissecting the ovaries of female deer throughout the mating season
    • He found no sign of an 'egg'
    • Note that he did not have access to a microscope during his work

NOS: Developments in scientific research follow improvements in apparatus; William Harvey was hampered in his observational research into reproduction by lack of equipment. The microscope was invented 17 years after his death

• In scientific research, critical developments often follow improvements in scientific apparatus
  • For example, distant objects in Space often remain undiscovered until a telescope, or some other piece of equipment, powerful enough to detect them is developed

• William Harvey was greatly held back in his observational research into reproduction by a lack of suitable equipment
  • The microscope was invented 17 years after his death
  • Harvey failed to solve the mystery of sexual reproduction because effective microscopes were not available when he was working
  • This meant he could not find and observe male and female gametes, so the fusion of gametes and subsequent embryo development remained undiscovered
    • In addition, Harvey's decision to use deer as a study species was unlucky, as deer embryos remain microscopically small i.e. small enough that they can only be viewed using a microscope, for an unusually long period of time

• Although the presence of sperm cells in semen was first reported in 1677, it wasn't until the 19th century that the fertilisation of an egg cell by a sperm cell was finally observed
  • This showed that something contained within the egg and the sperm was being inherited by offspring, which lead to a much greater understanding of sexual reproduction

• The fact that scientific research is often held back by a lack of sufficiently powerful or precise apparatus is a problem that will continue into the future
• In some ways this is very exciting, as it suggests that our scientific knowledge and understanding of the universe will continue to expand as new scientific techniques and technologies are developed