Some information that circulates about dogs just isn’t true. Here are some examples:
Mutts (mixed breeds) are healthier
Actually, any dog can have health problems but pure bred dogs commonly have more genetic disorders. Mixed breeds, according to many vets, have hybrid vigor. This term refers to superior qualities that appear when genetically different animals are crossbred. The technical term for hybrid vigor is heterosis.
Licking helps to heal a wound
This is not necessarily the case. Some dogs obsessively lick a wound and this does more damage than good. You should consult your veterinarian if your dog is worrying a sore or wound.
Puppies and dogs don’t need house training because they naturally know where to go (wolfs, from where dogs descended, won’t soil their den)
Nice try but most dogs and puppies need to be trained to do their business outside. Some dogs (like children) are easier to train.
If a dog wags its tail, its friendly and happy
This isn’t always the case. A wagging tail can mean a dog is excited or agitated. Unless you know a dog, the best precaution is to ask its owner before you pet it.
Only male dogs ‘hump’ or raise their leg to pee
Female dogs will also do this, particularly if they are dominant. Spaying does not affect this behavior.
DoggyMom.com 
Great information and so true there are many fallacies out there. Another one is that all dogs are good swimmers. Again not true. It does not come naturally to many breeds -especially pug-nosed ones and ones with short legs. Like people they need to learn to swim to keep them safe near and in the water. Thanks again for the great blog as it makes people aware of the truths about their pets.