Even crystals have random inclusions. Catalysis and replication without error is harder to achieve than catalysis or replication itself. On a DNA/RNA level, va

Even crystals have random inclusions. Catalysis and replication without error is harder to achieve than catalysis or replication itself. On a DNA/RNA level, various nucleotides have affinity not only for their normal partner, but less so for other partners. This becomes especially important as environmental damage (from the energetic systems we all live in) cause alterations in the chemical structure of the nucleotides. That's just one method of mutation.