I was proofing a professor’s  journal article about statistical analysis of the evolution of populations.  The article stated that populations and their genes can experience bottleneck events in which the population gets knocked way back. There are at least two subtypes of bottleneck event. The hourglass is when they rebound right away.  If, however, something keeps the population constricted for a time – it’s a longneck event!  What a metaphor.