## 1.1 How do we know what we know?

Scientists once believed that all life commonly and regularly arose spontaneously from non-living matter (‘spontaneous generation’); that is, any life form could be created on-demand from non-living things by following recipes.

J. B. van Helmont gave this recipe:

If a soiled shirt is placed in the opening of a vessel containing grains of wheat, the reaction of the leaven in the shirt with fumes from the wheat will, after approximately twenty-one days, transform the wheat into mice.

— Translation of

We now know that this isn’t true… But how did van Helmont reach this conclusion? Through observation: this is what he saw happen. And why was this idea rejected? Because of the scientific process.

Spontaneous generation was proposed after making observations. van Helmont then proposed a possible explanation (a hypothesis). This hypothesis was then rejected when evidence contradicted the hypothesis. So, a a new hypothesis was proposed and tested, based on further evidence. Briefly, this is the evidence-based, scientific process.

A more recent example of the scientific process in action is declaring cigarette smoking as harmful. As recently as 1978, the verdict on whether smoking is harmful was debated:

…many eminent persons, committees and commissions have unanimously concluded that lung cancer ‘is almost entirely due to cigarette smoking.’ I once shared this view, but having now studied the evidence in more detail and from new angles I feel unable to reach a definitive conclusion…

, p. 456

All scientific knowledge emerges in a similar way: Observations lead to hypotheses, which are tested against the evidence, and the hypotheses are either rejected or temporarily accepted based on this evidence. Notice the approach: hypotheses are rejected when contradictory evidence emerges, but hypotheses are only ever temporarily accepted until contradictory evidence emerges (if ever).

Knowledge in all scientific disciplines is based on a similar process:

• How do we know the gestation length for Gilbert’s Potoroo ?
• How do we know that paracetamol eases pain ?
• How do we know that exercise is good for us ?
• How do we know if permeable pavement technology is effective in reducing runoff ?

### References

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Curfman GD. Is exercise beneficial—or hazardous—to your heart? NEJM. 1993;329:1730–1.
Latour B. Pasteur et Pouchet: Hétérogenèse de l’historie des sciences [Pasteur and Pouchet: Heterogenesis of the history of science]. In: Serres M, editor. Eléments d’histoire des sciences [elements of history of science]. Paris: Bordas; 1989. p. 423–45.
Mullaney J, Lucke T. Practical review of pervious pavement designs. CLEAN–Soil, Air, Water. Wiley Online Library; 2014;42(2):111–24.
Stead-Richardson E, Bradshaw D, Friend T, Fletcher T. Monitoring reproduction in the critically endangered marsupial, Gilbert’s potoroo (Potorous gilbertii): Preliminary analysis of faecal oestradiol-17$$\beta$$, cortisol and progestagens. General and comparative endocrinology. Elsevier; 2010;165(1):155–62.
van Helmont J-B. On the necessity of leavens in transformations. In: Conte J. L., editor. Les oevres de Jean-Baptiste van Helmont. Lyon; 1671.
Weil K, Hooper L, Afzal Z, Esposito M, Worthington HV, Wijk A van, et al. Paracetamol for pain relief after surgical removal of lower wisdom teeth. Cochrane Database of Systematic Reviews. John Wiley & Sons, Ltd; 2007;(3).