When a female comes into heat and she is not confined she will find a fully male dog to mate with. If all of the fully male dogs are fertile and she is fertile the odds are she will become pregnant. If most male dogs get vasectomies instead of neutered then there is a good chance the male dogs she is mating with are going to infertile and she will not become pregnant. Neutring only takes the male out of the gene pool but males don't have babies so unless you get all of them the population is not affected. A few decades ago they released hundreds of millions of flies that had been chemically sterilized near San Antonio. Many of those flies bred with intact flies and two weeks later there were a lot less flies since every sterilized fly that mated with an intact effectively took that other fly out of the gene pool.


Most shelters require you to neuter a male dog or cat if you adopt one from there and the argument is that it is to control population. It seems pretty obvious that a better method is available if population control was the true goal. I object to them placing the moral weight of population control behind their insistence when it really has very little to do with population control. Why even insist on it to begin with if is only for behavior modification? If behavior is the goal why not require training? The cynical side of me suspects it is simply because it would offend the gender equality mindset that so many people hold. Now it has become a matter of faith and it doesn't matter if it actaully works.