&gt; a species is basically the pool of organisms available at a period of time that can generate progeny that themselves can generate progeny<p>That&#x27;s what we learned in high-school too, but as you mentioned, it doesn&#x27;t make sense for donkeys, nor does it work for ring species[1], or organisms that reproduce asexually[2].  Mules can occasionally become mothers[3].<p>1. <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Ring_species" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Ring_species</a><p>2. <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Asexual_reproduction" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Asexual_reproduction</a><p>3. <a href="http:&#x2F;&#x2F;www.npr.org&#x2F;templates&#x2F;story&#x2F;story.php?storyId=12260255" rel="nofollow">http:&#x2F;&#x2F;www.npr.org&#x2F;templates&#x2F;story&#x2F;story.php?storyId=1226025...</a>