conditional sentence without if

For the past four billion years or so the only way for life on Earth to produce a sequence of dna—a gene—was by copying a sequence it already had to hand. Sometimes the gene would be damaged or scrambled, the copying imperfect or undertaken repeatedly.

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to me, it sounds like "IF the copying (is) imperfect or undertaken repeatedly, sometimes the gene would be damaged or scrambled." It is conditional, why there is no "if" in the sentence. Is it a grammar rule?

I read it as three ways in which the data sequence of the 'copy' might be wrong: (1) original gene wrong (2) bad copying (3) copied too many times. But I think the text you are quoting isn't clear: "Sometimes the gene would be damaged or scrambled" might be referring to the new gene, or (as I think) to the original gene, in which case no "if" is required..