Section 1.1 Introduction: how we know what we know
Scientists once believed that all life regularly and commonly arose spontaneously from non-living matter. Recipes even existed; for example, [28] gave this recipe for making a mouse [68]:
Illustration of a mouse.
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.
This was called ‘spontaneous generation’ (or ‘abiogenesis’). This theory is clearly incorrect, so how did the idea emerge? How was it disproven? Through observation and research.
Spontaneous generation was consistent with observations: following the above recipe did produce mice. However, the hypothesis (‘possible explanation’) of spontaneous generation was rejected when later evidence, in better-designed research studies, contradicted the hypothesis. A new hypothesis was proposed to explain the appearance of the mice, which was tested against the evidence, and so on. Briefly, this is the evidence-based, scientific process.
As a more recent example, the dangers of smoking were still being debated into the 1990s:
… a causal role for smoking [has] not been proved beyond reasonable doubt.―[40], p. 429
All scientific knowledge emerges in a similar way: observations lead to questions and hypotheses, which are tested against evidence. If the evidence contradicts the hypothesis, the hypothesis is rejected. If the evidence is consistent with the hypothesis, the hypothesis is temporarily accepted (until any contradictory evidence emerges, if ever).
Hypotheses not contradicted by large amounts of evidence, over a long time, are sometimes called laws or theories (such as the ‘Law of conservation of energy’). Theories and laws can be disproven if contradictory evidence emerges. Knowledge in all scientific disciplines is accumulated using a similar evidence-based process.
