Select the option that gives the correct description of the process of Natural Selection with respect to the length of the neck of giraffe.

The correct options are:
1. "Directional selection as giraffes with longer neck lengths are selected."
2. "Stabilising selection as giraffes with medium neck lengths are selected."

1. Understanding the Graph:
The provided image shows a bell-shaped normal distribution curve. The horizontal axis (x-axis) represents the trait "Neck length in giraffe", and the vertical axis (y-axis) represents the "Number of giraffes". This curve shows that within the giraffe population, there is natural variation in neck lengths, with most individuals clustered around the average or medium length.

2. Why Directional Selection is Correct:
Historically, giraffe ancestors had much shorter necks. When competition for food on lower tree branches increased, individuals with slightly longer necks had a selective advantage because they could reach foliage on taller branches. Over generations, this environmental pressure favored the extreme phenotype of longer necks, shifting the entire population distribution toward the longer-neck trait. This progressive shift in one direction is known as directional selection.

3. Why Stabilising Selection is Correct:
Once an optimal neck length is reached and the environment remains stable, extreme variations are selected against. Giraffes with necks that are too short cannot feed efficiently, while those with excessively long necks may face physiological challenges (such as pumping blood to the brain or structural instability). Therefore, natural selection favors the intermediate or medium neck length, narrowing the distribution around the mean. This process of maintaining the status quo by selecting for the average phenotype is known as stabilising selection.