The bacterial immune system: identifying evolved defense adaptations.

A four-part framework is proposed to identify bacterial defense mechanisms as evolved adaptations, addressing the lack of consensus in the expanding 'bacterial immune system'.

• Why it matters: Understanding whether bacterial defenses are true evolutionary adaptations matters for clarifying their roles in microbial survival and informing microbiological research.
• What they did: The authors review debates in evolutionary biology and develop a four-part criteria-based framework to evaluate defense mechanisms as evolved adaptations, applicable beyond bacterial immunity.
• The result: This framework offers a research roadmap to resolve functional controversies and advance understanding of bacterial defense mechanisms as evolutionary adaptations.