I wasn&#x27;t familiar with the term &quot;Ring Species&quot; (I&#x27;ve only gotten interested in evolutionary biology in the past few years), although I had considered that a &quot;pool&quot; might have a relatively fluctuating degrees of mutuality and incompatibility among candidate members.<p>Also, I hadn&#x27;t considered to qualify &quot;sexual reproduction&quot;, as asexual reproduction might be better thought of as strains (perhaps), the classification systems for simpler organisms tends to be more structural than fecund.  In my defense, I tend to refer to organisms as assemblages of organs of which simpler biota can loosely be said to possess, though I always thought of the &quot;organs&quot; of single-cellular creatures as organelles as they are not made up of &quot;tissue&quot; as they are in multi-cellular organisms.