ืno two livings things are born exactly the same even identical twins have some differences. often the differences are not important.but sometimes they can be important. but sometimes they can be important. this difference may improve the animals spring.after many generations.only individuals of that species with the useful variation are left. for example giraffes with the longest necks will be able to reach and food is in short supply giraffes with longer necks will be able to get more to eat than other giraffes and may be the only ones to survival of the fittest which is part of natural selection first suggested by naturalist charles drawin. he noted that birds beaks are different shapes so that they can ea t different kinds of food. these changes occurred over a very long period of time by small adaptations.