Giraffes use their extremely long necks to reach the leaves high up on acacia trees, which other animals cannot reach, giving them a food source for which they have few competitors. what can you conclude about natural selection from this observation giraffe necks get longer over a lifetime of stretching, and their offspring inherit the longer necks of their parents. all giraffes are born with short necks and, eating acacia leaves causes them to stretch over a lifetime. other animals will mimic the giraffe and grow longer necks. the giraffes with the longest necks survive and produce offspring