Most existing LLM safety evaluation and defense methods are static: jailbreak vulnerabilities are assessed with fixed attacks, and guardrails are trained on fixed malicious-prompt datasets. In practice, adversaries continually evolve and expand the attack space. We propose DARWIN, an evolutionary attack-defense framework that models jailbreaking as a continual process and updates guardrails through an attack-defense loop. DARWIN-Attack evolves its capabilities through strategy discovery, mutation, selection, and feedback-guided composition. It mines strategies from broad external sources, generates variants through self-reflection and genetic evolution, filters them by performance against aligned LLMs, and adaptively selects and composes strategies during attacks. Through continuous evolution, DARWIN-Attack achieves state-of-the-art attack success rates against frontier LLMs and guardrails, reaching nearly 100\% on DeepSeek-V4-Pro, over 90\% on GPT-5.5, and nearly 100\% on YuFeng-XGuard, outperforming recent evolving frameworks such as LSA and MAGIC. Its continued evolution exposes new vulnerabilities, motivating timely defense updates. Accordingly, DARWIN-Guard performs online adversarial training on emerging samples generated by DARWIN-Attack and jointly learns from malicious and benign disguised queries to recognize underlying intent rather than superficial attack patterns. DARWIN-Guard achieves 95.0\% average unsafe recall across multiple safety benchmarks, outperforming recent advanced guardrails such as YuFeng and Nemotron, while maintaining nearly 100\% average benign pass rate on standard benign benchmarks and the best performance on over-refusal benchmarks. Our code and model are available at https://github.com/ZJU-LLM-Safety/DARWIN.

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