There are many breeds of poultry and many different genetic makeups of birds. There are around 300 breeds of chickens that have been developed over the time man has domesticated them.
Most all poultry kept that are not species have been selectively bred by people. Barred Rocks, Delawares, and Runner ducks are all examples of this.
Species breeds are the naturally occurring breeds like the Gray Jungle Fowl or Mandarin Ducks in their naturally occurring forms.
With so many different chicken and other poultry breeds available one should do some research into the breed before adding it to the collection. Especially for those other than chickens. Ducks, pheasants, and quail can have many different requirements from each other than breeds of chickens may have.