Darwin's Theory of Evolution

Charles Darwin's book titled "On the Origin of Species" introduced the theory that populations evolve over the course of generations through a process of natural selection. Darwin's book was the culmination of evidence he had accumulated on the voyage of the Beagle in the late 1830s and expanded through continuing investigations and experiments after his return.

Essentially the concept of natural selection means that individuals best adapted to their environments are more likely to survive and reproduce. As long as there is some variation between them, there will be an inevitable selection of individuals with the most advantageous variations. If the variations are inherited, then differential reproductive success will lead to a progressive evolution of particular populations of a species, and populations that evolve to be sufficiently different might eventually become different species.

One of the locations visited by Darwin during his voyage on the Beagle was to the Galapagos Islands. On the Galapagos Islands he noticed the slight variations that made tortoises from different islands recognizably distinct. He also observed a whole array of unique finches that exhibited slight differences from island to island. In addition, they all appeared to resemble, but differ from, the common finch on the mainland of Ecuador, 600 miles to the east. Galapagos finches are the famous example from Darwin's voyage. Each island of the Galapagos that Darwin visited had its own kind of finch (14 in all), found nowhere else in the world. Some had beaks adapted for eating large seeds, others for small seeds, some had parrot-like beaks for feeding on buds and fruits, and some had slender beaks for feeding on small insects. One used a thorn to probe for insect larvae in wood, like some woodpeckers do. (Six were ground-dwellers, and eight were tree finches.) (This diversification into different ecological roles, or niches, is thought to be necessary to permit the coexistence of multiple species.) To Darwin, it appeared that each was slightly modified from an original colonist, probably the finch on the mainland of South America, some 600 miles to the east. It is probable that adaptive radiation led to the formation of so many species because other birds were few or absent, leaving empty niches to fill; and because the numerous islands of the Galapagos provided ample opportunity for geographic isolation. Similar conclusions were drawn from observing the Galapagos tortoises.

During our Environmental Studies class we observed many different turtles and tortoises. There is a clear indication that through natural selection, the different species I examined have over time, developed adaptations specific to their habitats that have allowed them to survive.
For example the snake-necked turtle has a unusually long neck. This unique characteristic gave the snake-necked turtle the ability to survive over other species because of their extended reach making it easier to capture prey.
Another turtle we observed was the soft shell turtle. The adaptation developed by this turtle is a smooth streamlined shell allowing it to swim at faster speeds than other turtles, decreasing its chances of being captured by predators.
The adaptations found on the different species around the world were developed over long periods of time through the process of natural selection, making each specie special and unique.


Sources
Evolution and Natural Selection
http://www.globalchange.umich.edu/globalchange1/current/lectures/selection/selection.html
Wikipedia.org