Question: How & why do creatures evolve?

Lyndsey Fox answered on 15 Jun 2011:

Yay! I love discussing evolution!

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.

And that’s it! Well not really, it can get massively complicated if you start looking at it closely. I’m happy to go into as much detail as you want. This is party what I research for a living!