All mammals, including giraffes, have 7 cervical (neck) vertebrae. Giraffes have a longer neck than other mammals because during their development, the cervical vertebrae grow for longer than in other mammals and thus become larger. The difference in neck length between giraffes and other mammals is thus attributed to Question 13 options: heterochrony analogy allopatric speciation convergent evolution exaptation heterochrony analogy allopatric speciation convergent evolution exaptation.