Originating as a popular form of entertainment in 19th-century Europe and later as a sideshow exhibition in North American traveling carnivals and vaudeville halls, professional wrestling grew into a standalone genre of entertainment with many diverse variations in cultures around the globe, and is now considered a multimillion-dollar entertainment industry. While it has greatly declined in Europe, in North America it has experienced several different periods of prominent cultural popularity during its century and a half of existence. The advent of television gave professional wrestling a new outlet, and wrestling (along with boxing) was instrumental in making pay-per-view a viable method of content delivery.
Where was wrestling later showcased in North America?
later as a sideshow exhibition in North American traveling carnivals and vaudeville halls

This effectively means that populations of organisms must have reached a certain measurable level of difference to be recognised as subspecies. Dean Amadon proposed in 1949 that subspecies would be defined according to the seventy-five percent rule which means that 75% of a population must lie outside 99% of the range of other populations for a given defining morphological character or a set of characters. The seventy-five percent rule still has defenders but other scholars argue that it should be replaced with ninety or ninety-five percent rule.
What must organisms have a measurable level of to be seen as a subspecies?
difference

Mutations or deletions of clock gene in mice have demonstrated the importance of body clocks to ensure the proper timing of cellular/metabolic events; clock-mutant mice are hyperphagic and obese, and have altered glucose metabolism. In mice, deletion of the Rev-ErbA alpha clock gene facilitates diet-induced obesity and changes the balance between glucose and lipid utilization predisposing to diabetes. However, it is not clear whether there is a strong association between clock gene polymorphisms in humans and the susceptibility to develop the metabolic syndrome.
What do mice without the clock gene become?
hyperphagic and obese