Striving for clarity about the “Lamarckian” nature of CRISPR-Cas systems

Koonin argues that CRISPR-Cas systems present the best-known case in point for Lamarckian evolution because they satisfy his proposed criteria for the specific inheritance of acquired adaptive characteristics (IAC). We see two interrelated issues with Koonin’s characterization of CRISPR-Cas systems as Lamarckian. First, at times he appears to confuse an account of the CRISPR-Cas system with an account of the mechanism it employs. We argue there is no evidence for the CRISPR-Cas system being “Lamarckian” in any sense. Second, it is unclear whether the mechanism is more “Lamarckian” than many other forms of genetic change already well-characterized in Darwinian terms. We present three conceptually distinct senses in which the mechanism of IAC may be considered Lamarckian and argue that only the strongest sense of goal-directed IAC would be difficult to accommodate in a Darwinian account. As the CRISPR-Cas mechanism does not qualify as “Lamarckian” in this strong sense, we argue there is no conceptual value in calling it “Lamarckian”. Finally, we suggest that CRISPR-Cas systems do hold the potential for genuinely non-Darwinian, directed evolution in a way that Koonin did not discuss, involving their potential (mis)use as a human gene-editing tool.