Ponies on the Shetland Islands in Scotland have short stature, thick hair, strength, and hardiness so they can thrive in their harsh environment. How do you think the DNA of their population has changed over time?

To adapt to the environment for optimal survival

Explanation:

The nature of the environment in Scotland puts selective pressure on the population of Shetland Island donkeys. Interestingly, these donkeys are not intermingled with any other species. It is said that these animals have inhabited the island for over 2000 years but may have existed there since the Bronze Age.

These animals arrived to the island by way of the Celtic people who created the species by crossing a original mountain pony with an Asian type horse. Speciation occurred when the ponies adapted to their environment without other interfering genetic pool.

Generally speaking, the population DNA hasn't undergone a multitude of change; but adaptation remains key for survival.