As many of you know, I've taken quite the interest in science, especially biology. It's been well over 150 years since Charles Darwin gave the world the first scientific evidence and explanations for evolution. Yet there is considerable number of Americans who deny it or just don't understand it. While I don't consider myself a evolutionary expert, I'd like to explain the process in my own way.
To understand evolution, I think it's easier to start on why it happens than to guess the earliest common ancestor to all life. All of the life on Earth from animals, plants, bacteria, etc. all have DNA. When a living thing is born, it is no accident that it grows to be what is eventually becomes. DNA determines almost everything about you. In most living things, there are two parents that pass their genes on to the next generation, but what happens when there is a trait that neither parents (nor their ancestors) possess appears?
This is called a mutation, and it should not be confused with its exaggerated use portrayed in comic books. Mutations are typically very small changes though they can be important enough to severely change an organism for better or for worse. What causes an mutation? Naturally it can happen in error when DNA fails to perfectly replicate itself among others. Outside forces such as chemicals, radiation, and ultraviolet light can cause mutations as well.
Dogs for example were descended from wolves (something that has been genetically proven) thousands of years ago. Random mutations in fur color, facial features, temperament, etc. had gotten humans to separate dogs with new traits and over time created a new breed of dog. Countless years of this has led to the countless types of dogs we know and love. This is called artificial selection in evolution.
But in many evolutionary studies, sometimes stuff is an educated guess. Scientists had believed that penguins evolved around Antarctica or New Zealand, but later found fossils of a giant Penguin species. It had lived in present-day South America, and had led scientists to rethink the evolutionary history of penguins. While there are many gaps in the history of life and evolution doesn't mean it's not real. A scientific theory should not be confused with a hypothesis as gravity and relativity are both "theories" as well.