Thousands of years ago, giraffes with short necks were common within giraffe populations. Nearly all giraffe populations today have long necks. Which of the following most likely caused the giraffe's neck to lengthen?
a
the artificial selection of an advantageous trait
b
the natural selection of a disadvantageous trait
c
a genetic mutation in the reproductive cells of giraffes
d
a genetic mutation in the skin cells of giraffes
a
the artificial selection of an advantageous trait