A species is a group of organisms that can breed together to form fertile
offspring.Therefore these organisms are usually very similar.
For example two dogs can breed together because they are from the same
species however a dog and a cat cannot.
Organisms of the same species can be selectively bred with each other to
produce favorable characteristics.
For example different varieties of dogs can be bred together or can also be
done in cows.
In cows, different varieties are chosen because of the amount of milk that they
Therefore the process involves choosing two cows that produce a lot of milk,
and allowing these cows to breed. Once the offspring have been produced,
let them breed until you have a breed that has the characteristics that you