6.2 Applications and skills

6.2.6b The mystery of reproduction: IVF and William Harvey

  • IVF is a form of assisted reproduction that is available to people who are unable to conceive naturally due to infertility.
  • IVF involves using drugs to suspend the normal secretion of hormones, followed by artificial doses of hormones to induce superovulation. Eggs are harvested and fertilised outside of the body, and then implanted in the uterus to establish pregnancy.
  • William Harvey’s study of reproduction in deer is related to many themes in the nature of science.

IVF - in vitro fertilisation

One cycle of IVF takes between four and six weeks. The success rate for women under 35 is about 40%. For women over 35, it is about 20%.

Figure 6.2.6b.a - The IVF processFigure 6.2.6b.a – The IVF process

Hormonal control is essential during all steps:

Ovarian hyperstimulaton
  • The menstrual cycle is suspended with drugs that suppress the release of LH and FSH from the pituitary gland. (This allows follicular development to be better controlled and timed.)
  • Over the next week or two, high-dose intramuscular injections of FSH are administered to stimulate the development of many follicles at the same time.
Egg retrieval
  • When the follicles are large enough, another hormone, called hCG, is administered. hCG stimulates ovulation because it is functionally and chemically similar to LH.
  • Eggs are retrieved before they are released exactly 36 hours after hCG injection. The patient is under general anaesthetic.
  • Fluid from the ovaries is removed directly using a guided needle. Up to 12 eggs may be removed at once.
Fertilisation and culture
  • Not all the eggs are mature, or viable.
  • Viable eggs are fertilised under a dissecting microscope with a small needle.
  • The fertilised eggs are incubated until they reach a blastocyst stage (five or six days).
Transfer and implantation
  • Blastocysts are implanted directly into the uterus. No anaesthetic is needed.
  • Sometimes, the patient may choose to implant more than one embryo to increase the chance of a successful pregnancy.

William Harvey’s investigation of reproduction in deer

  • In the 17th century and 18th centuries, there was an important debate on the study of reproduction. Some scientists believed in preformationism, whereby an embryo developed from particles that were simply smaller versions of the adult animal.
  • On the other side of the debate was a more developmental philosophy called epigenesis, which proposed that an embryo takes on human characteristics as it develops through a process of differentiation. In Ancient Greece, Aristotle proposed this philosophy. He believed sperm when mixed with menstrual blood held all the material for development. The female provided the ‘fertile ground’ for the male ‘seed’.
  • William Harvey was educated in Aristotle’s philosophy, but after studying chicken embryos developing in eggs, carefully documenting differentiation and the stages of embryonic development, he wanted to prove that omne vivum ex ovum, or ‘every living thing comes from an egg’, including mammals and humans.
  • He thought it would be easier to observe eggs in the uterus of large mammals, so he slaughtered deer that had recently mated, and opening the uterus, he searched for eggs or other early signs of embryonic differentiation. He was not able to observe anything in the initial stages.
  • Harvey was not able to identify eggs because he was limited by his equipment – a simple hand lens. Microscopes allowed the observation of the first sperm cell in 1877, and the first mammalian egg nearly 200 years after Harvey, in 1826.

Nature of Science

Developments in scientific research follow improvements in apparatus: William Harvey was not able to visualise sperm or egg cells, as the microscope was invented 17 years after his death.

Figure 6.2.6b.b - Dissecting microscopeFigure 6.2.6b.b – Dissecting microscope
In IVF, dissecting microscopes allow the technician to manipulate the egg and sperm while observing them.

Figure 6.2.6b.c - In vitro fertilisationFigure 6.2.6b.c – In vitro fertilisation

Figure 6.2.6b.d - A blastocystFigure 6.2.6b.d – A blastocyst

Concept help

  • Infertility may be the result of a low sperm count or motility in the male partner, or fibroid polyps or other obstructions in the fallopian tubes of the female partner.
  • Natural fertility in women declines rapidly after the age of 35.
  • Single women or same-sex couples without fertility issues would probably use IVF only after attempting less invasive procedures (such as intrauterine insemination, also known as ‘artificial’ insemination).

Course link

  • Human chorionic gonadotropin, hCG, is naturally produced during pregnancy. HL students will learn more about it in Page 11.1.4.

Language help

  • In vitro is Latin for ‘in glass’. Fertilisation takes place in a petri dish.
  • In vivo is Latin for ‘in the living’. Fertilisation takes place in the fallopian tube.
  • Epigenetics is the (modern) branch of biology concerned with inheritable processes that do not directly involve DNA. Do not confuse this term with epigenesis, which is an (outdated) Aristotelian theory of development.

Figure 6.2.6b.e - PreformationistFigure 6.2.6b.e – Preformationist
Nicholas Hartsoeker (1656–1725) was a preformationist who imagined that sperm were made of tiny ‘men’. He made this drawing in 1695.


The ‘preformation–epigenesis’ debate has a modern face: the ‘nature–nurture’ debate. How far have we come in resolving it?