"A familial generation is defined as the average time between a mother's first offspring and her daughter's first offspring. The generation length is 25.2 years in the United States as of 2007..." That's for humans but a familial generation for animals is usually much shorter. All that is necessary to destroy a species or breed is to disrupt a single familial generation or, to be safe, keep it disrupted for 2 generations. 5 years would do it for all our beloved pets and most of the agricultural livestock.
“We have no ethical obligation to preserve the different breeds
of livestock produced through selective breeding ...One generation and
out. We have no problems with the extinction of domestic animals. They
are creations of human selective breeding.” Wayne Pacelle of HSUS.
— Animal
People News, May 1993
My family has homes in Texas and Missouri and I can't help but notice what is going on back at "the farm" and feel that both my homes are just plain under siege. One generation and out applies to pets just as it does to livestock. I have Shibas and Labradors. They are both dogs but they are special and different BECAUSE of their breeding. They certainly aren't the best bred of dogs but, even with that, what is special about each breed SHINES through.
http://www.youtube.com/watch?v=ettJtlmr4wM&feature=player_embedded
More at HumaneWatch.org
If you ask me, we women might should be a little more selective about who we breed with to prevent more Wayne Pacelle and Ingrid Newkirk style genes from being passed along. Ladies, nurture can only overcome SOME of nature and even then it's hard work. Save yourself, choose better to start with.