extinct by the 10th generation

The strength of sexual selection ranged from intense competition — where 90 males competed for only 10 females — through to the complete absence of sexual selection, with monogamous pairings in which females had no choice and males no competition.
After seven years of reproduction, representing about 50 generations, the scientists found that populations where there had been strong sexual selection were fitter and more resilient to extinction in the face of inbreeding.
But populations with weak or non-existent sexual selection showed more rapid declines in health under inbreeding, and all went extinct by the 10th generation.
end quote from:
http://www.abc.net.au/news/2015-05-19/why-do-men-exist-scientific-study-offers-an-explanation/6480198

So, the reason for the necessity in all species with both males and females including humans to have intense competition among the males to mate with females is to protect against inbreeding when it occurs so whole lines of people and animals don't go extinct by the 10th generation.

This might be important among dog breeders so they don't just breed their species of Dog or Cat out of existence in the 10th generation too.

This also could be a problem maybe in Beekeeping too worldwide and in all species of animals and birds and insects that people breed for profit or as a hobby.