The Sewall Wright effect 
The Sewall Wright effect often occurs when this law does not hold.  One of its namesakes disliked applied mathematics and would later work with Littlewood on Diophantine analysis and tutor Ramanujan. He developed this rule concurrently with a German physician.  The disagreement between this law and reality provided support for natural selection, because it holds in the absence of migration, mutation, selective mating.  FTP, name this doubly-eponymous law of population genetics employing the equation p plus q equals one.      ---|---          |
The Sewall Wright effect often occurs when this law does not hold.  
{Hardy-Weinberg} Law or Equilibrium or Rule or Equation, accept equivalents