&gt; What makes you say that? Is there some underlying principle I&#x27;ve failed to consider?<p>Low fertility rates is a statistical rule.  It&#x27;s not absolute.  There will always be people with high fertility, at the very least because they will be at the edge of the bell curve.  Also again, look at religious communities, like the Amish.  Those people do exist.  Among seven billion human beings, you certainly can find a few millions that are very much willing to make babies.  It only takes a small minority to ensure that the numbers will not go to zero.<p>&gt; The natural universe has no favorites. It does not preclude this sort of extinction.<p>The lineage of people who don&#x27;t have children will simply disappear, leaving room for the lineage of people who do.  It&#x27;s as simple as that.<p>&gt; Why would they rise?<p>The fertility rate will rise because people with low fertility rate will die with no children.  What will remain will be the children of people with high fertility rate, and presumably those children will have a similar reproductive behavior than their parents.  Low fertility reproductive behavior will be &quot;naturally&quot; filtered out.<p>&gt;  Those few who buck this trend will be starved for adequate mates at some point, and will raise their own children in a culture that ostracizes fertility...<p>Fertility declines, but it&#x27;s quite a stretch to talk about ostracization of fertility.  And ostracization is not prohibition.