However, Darwin's theory faced many problems related to Lamarck's laws. Lamarck and Darwin fully understood the importance of variation, and it is their understanding of variation that fundamentally separates these two evolutionary theorists. However, Darwin had relatively little to say about the sources of variation, which was a constant source of frustration for him. Lacking a model of variation, he mainly focused on selection mechanisms, which influence the traits found within a population (Gilady, Hoffmann., 2013). Darwin's natural selection suggests that biological information is passed on to subsequent generations simply through a DNA sequence and leaves no room for hereditary phenotypic variations acquired over the course of an organism's life, which contrasts with Lamarck’s visions on evolutionary change (THORÉ., 2015). The example of the giraffe's neck given by Lamarck can easily be used to prove that Darwin's theory is correct. Although Lamarck's model was incorrect, the question of how giraffes developed such long necks has remained an important question in the topic of evolution; however, this can be explained using the study of DNA and Darwin's theory of evolution. According to this theory, giraffes with longer necks are able to eat more leaves, making them healthier and more likely to produce offspring. The genes, or DNA, that code for this long neck are inherited by their offspring, causing their offspring to also have longer necks. Over the years, the number of descendants carrying “long neck” genes exceeds that of descendants carrying “normal neck” genes. Eventually, the "normal neck" genes are wiped out because they are unable to reach larger trees and feed adequately, making it difficult for them to survive and survive..