"Isolating mechanisms are biological properties of individuals that prevent the interbreeding of populations that are actually or potentially sympatric."

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Never give children a chance of imagining that anything exists in isolation. Make it plain from the very beginning that all living is relationship. Show them relationships in the woods, in the fields, in the ponds and streams, in the village and in the country around it. Rub it in.

— Aldous Huxley