Because some animals have diffrent instincts, perhaps like dogs, any type of dog is a relative of the wolf. Some wolves in some areas of the world have actually tolerated the presence of humans, just...
some animals develop wings. others get it from traits. such as genetic traits.others well i dont know about that
Because some don't have the ability. That's true for individuals, As a species, all multi-celluar animals must mate or else become extinct.
Well the Dog,Cat,Snake even though it may be a reptile I have on to pet,and also a Horse,Cow,Chicken,Bird and many many more :)
Worms, fleas, ticks and other parasites