Everyone has their own theory of evolution, yet some are more complex and can explain more about the current creatures on Earth. All of the evolutionary theories say partially the same thing, that life changes over time, but there are also many explanations as to how that happens. For instance, the theory of Charles Darwin and the theory of John Babtiste Lemarck differ in many ways. .
Studying in the Galapagos Islands, Darwin came up with his theory. His theory was completely about survival of the fittest. Darwin believed in natural selection, a species being chosen for or against. Those creatures chosen for had a greater chance of surviving. They were considered to be the "fittest". However, those chosen against had a much smaller chance of existing because they were not fit and capable to live in their surrounding environment. .
Jean Baptiste Lemarck had a complete different theory on the other hand. He believed in a desire to change. For example if a creature needed something to survive it would grow it, and if it wasn't needed it would disappear. Also, after gaining or losing a body part, the creature would pass this trait on to their offspring. .
Based on Lemarck's theory, creatures would adapt to their environment. A giraffe for example, would acquire a trait if needed. To reach the tall leaves on the top of the tree, the giraffe slowly evolved, neck growing all the time until their necks were as long as the giraffes as we know them.
Based on Darwin's theory giraffes must have been a fit species in order to survive. The long neck would have given an extra advantage to it, being able to reach the food on the top of the trees, and the other short-necked animals would slowly begin to die off for lack of adequate body parts. .
Obviously, these two theories are completely different, yet I find it highly un-likely for Lemarck's theory to be real. I honestly can't believe that body parts would just grow or disappear.