Final answer:
Giraffes with longer necks had an advantage in reaching leaves, leading to the passing on of the long-neck trait to their offspring through natural selection.
Step-by-step explanation:
Giraffes with longer necks had an advantage as they could reach leaves other giraffes could not. This gave them a greater chance of survival and reproduction, leading to the passing on of the long-neck trait to their offspring. Over time, the population of giraffes consisted mostly of long-necked individuals.
This survival advantage is an example of natural selection, a key concept in biology. Natural selection favors traits that help organisms adapt to their environment and increase their chances of survival and reproduction. So, the giraffe with the long neck would be the one left to pass on its genes.