Giant Galapagos Tortoises are one of the oldest living animals on earth.
Believed to be capable of living more than 200 years, individuals as large as this one might have been on the earth when Charles Darwin made his famous journey in 1835 upon the HMS Beagle.
That historic journey brought Darwin to a world where the animals had been isolated from other populations of the same species.
Darwin observed that there were unique differences in the physical characteristics of the animals that differentiated them from the same animals on other continents.
It was these differences, or adaptations, that told Darwin that animals changed slightly from one generation to the next.
Darwin concluded that the physical changes were brought about by the differences in the environment and that required adaptation to increase survival.
Since the individuals that adapted were more likely to survive and more likely to pass on their genes through breeding, this created populations that possessed the same characteristics.
Simply put, this was the theory of evolution.
The finches and iguanas on these islands all have significant adaptations that help them survive in a harsh climate, as do most of the animals here.
These tortoises are no exception.
The tortoises are descended from the giant tortoises that roam Africa, but their shells are shaped differently.
During dry seasons, vegetation becomes sparse and the tortoises need to reach higher into the shrubs to access leaves and shoots.
Their reach of their long necks was limited by the shell behind their heads.
Those with grooves or indentations in the shell were able to reach higher.
Their increased survival meant that there would be more offspring produced by tortoises with this characteristic.
Incremental changes occurred over many generations to produce tortoises with the curved carapaces that we see today.
This tortoise has been spotted walking leisurely along the bike path on Santa Cruz Island in the Galalpagos.
A nature guide has stopped to capture video and to let his children see the tortoise as he passes on his knowledge about the fascinating animals.
Weighing as much as 220kg (485lbs), these enormous tortoises have little to fear when they are full grown.
Residents of the islands have great respect for the wildlife here and they understand the delicate balance that keeps their ecosystems running smoothly.
Tortoises are protected and interfering with them is avoided whenever possible.
A trip to the Galapagos Islands isn't complete without a close look at these ancient beasts.