The basic theory of evolution is surprisingly simple. It has three essential parts:
- It is possible for the DNA of an organism to occasionally change, or mutate. A mutation changes the DNA of an organism in a way that affects its offspring, either immediately or several generations down the line.
- The change brought about by a mutation is either beneficial, harmful or neutral. If the change is harmful, then it is unlikely that the offspring will survive to reproduce, so the mutation dies out and goes nowhere. If the change is beneficial, then it is likely that the offspring will do better than other offspring and so will reproduce more. Through reproduction, the beneficial mutation spreads. The process of culling bad mutations and spreading good mutations is called natural selection.
- As mutations occur and spread over long periods of time, they cause new species to form. Over the course of many millions of years, the processes of mutation and natural selection have created every species of life that we see in the world today, from the simplest bacteria to humans and everything in between.
Billions of years ago, according to the theory of evolution, chemicals randomly organized themselves into a self-replicating molecule. This spark of life was the seed of every living thing we see today (as well as those we no longer see, like dinosaurs). That simplest life form, through the processes of mutation and natural selection, has been shaped into every living species on the planet.
Can such a simple theory explain all of life as we know it today? Let's start by understanding how life works and then look at some examples.