# Hard Fork > **Machine-Evolution Nexus:** [[articles/Digital Darwinism and the Invisible World of Machine Evolution|Digital Darwinism and the Invisible World of Machine Evolution]] places this node within the history and governance of substrate-independent evolution. **Domain:** Blockchain / Lineage **Doc Type:** Canonical Wiki Node **Maturity:** Developed ## Definition A hard fork is a protocol change incompatible with prior rules, potentially causing a blockchain lineage to divide if participants continue both rule sets. ## Nexus Context The DAO fork and the Bitcoin–Bitcoin Cash split are deliberate cases of branching descent followed by economic and infrastructural selection. ## Evidence Boundary A fork copies prior state and creates descendants, but is not necessarily Darwinian evolution. The source of variation, reproduction pattern and selection mechanism remain human and technical. ## Relationships [[wiki/Branching Descent|Branching Descent]], [[wiki/Ethereum Classic|Ethereum Classic]], [[wiki/Bitcoin Cash|Bitcoin Cash]], [[wiki/Forked Continuity|Forked Continuity]] ## Sources / Provenance - Ethereum.org fork timeline; Bitcoin protocol history.