An example of an analogy used by a scierntist,
"The overwhelming majority of living organisms, from the lowest bacteria to trees and men, are all built of a relatively small number (about thirty in all) of types of chemical molecules containing between four and forty atoms in each. Every chemical molecule has its origin in some previous combination, as certainly as every atom of every element. More complex forms, particularly in this or that organism, can be derived from those simple types, and the few cases which have been studied have been shown to be so derived.
From this it follows that there is only one predominating life, derived from one common chemical basis. This is exactly the same logic that shows, for example, that all so called Indo-European languages have a common set of root words, however much they have deviated afterwards."
J. D. Bernal (1951) The Physical Basis of Life, Routledge and Kegan Paul
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Many examples of science analogies are listed in 'Creative comparisons: Making science familiar through language. An illustrative catalogue of figurative comparisons and analogies for science concepts'. Free Download.