Most commonly, evolution is discussed in terms of speciation, where a common ancestor's progeny adapt to different environments across generations, and start diverging in traits - thus, the same Prunus will give rise to the cherry and the apricot. But in some cases, evolutionary pressure can take different organisms to evolve similar, or, in this case, identical traits. Coffee and tea, for example, do not have the identical enzymes, but they have evolved to produce the same effect on the raw material xanthosine, in an identical chain of events that produces chemically identical caffeine. Which probably first evolved as chemical protection against insects.
---Steve
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