Natural selections leads to adaptations in a population that are physically or behaviorally suited to survive and reproduce in a particular environment. The organisms with the advantageous gene or trait leads to an increase in future generations of more organisms with that trait and decrease in those without that specific advantageous trait needed for survival.
Principle 2: Overproduction and the Struggle to Survive
The giraffes with a long neck are able to reach higher trees and do not have to compete as much for food with other herbivores as those giraffes with short necks. Their altitude also allows them to spot predators from a distance.
Principle 3: Survival and Reproduction of the Fittest
The giraffes show genetic variation of neck length. Due to a mutation in their DNA, some of the giraffes in the population have shorter necks than the typical long necks.
Principle 4: Changes in the Gene Pool
Overpopulation occurs and more giraffes are produced than the environment can handle. There is limited food and space and those giraffes that can obtain food survive while the others struggle to do so.
The giraffes with a long neck are able to obtain food from the tops of trees making it easier for them to compete against other herbivores for food as well. With this advantage, they are also able to spot predators from that altitude. They will survive and reproduce offspring with that gene.
The long neck gene will become more common in the giraffe population as they reproduce. The short neck gene has a very small chance of being passed on in a mainly long-necked giraffe population that was able to survive.