 Examination of adaptive immunity in prokaryotes provides a major breakthrough in this controversy. Many bacteria and most Archaea undergo non-random changes directed at devising protection from invasive bacteriophages and mobile genetic elements (Horvath and Barrangou 2010). These microbes use specialized methods of defense, CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats)-Cas (CRISPR-associated protein) systems to incorporate foreign DNA fragments into their genomes (Koonin 2019). These become templates for the formation of RNA molecules, which when associated with endonuclease enzymes, mediate destruction of the complementary, foreign DNA fragments. These acquired adaptive changes are a direct consequence of the organism’s interactions with the environment, and, because these modifications can be passed on to succeeding generations, the CRISPR-Cas system has been suggested to operate on Lamarckian principles, an interpretation that has been contested (Koonin 2012: 265; Koonin 2019; Pradeu 2019). Although not conforming to the neo-Darwinian model, this system lacks the teleological character postulated by Lamarck, and thus should be considered, at most, a model of directed mutagenesis (Wideman et al. 2019; Woolley et al. 2019; Weiss 2015). Others counter that a continuum of Lamarckian-Darwinian mechanisms exists in nature and that CRISPR-Cas represents a genuine case of Lamarckinism (Jablonka 2019; Koonin and Wolf 2016). Advocates of this latter interpretation place CRISPR-Cas systems among other apparently Lamarckian mechanisms like those mediating epigenetic inheritance (Gissis and Jablonka 2011).