I thought I’d throw out a quick definition of evolution, since there are lots of misconceptions about it.
It’s really not hard. Evolution is simply biological change over time. That’s it.
There are two big misconceptions regarding what evolution actually is.
First, there is all too often a conflation between evolution and natural selection. Natural selection is a mechanism of evolution. It’s just one of the ways in which evolution occurs. Natural selection occurs because certain adaptations, such as a stronger beak or better vision, give an animal the advantage when it comes to surviving until it is able to reproduce. Natural selection leads to evolution—biological change—because adaptation is, ultimately, change. Very slow change.
Second, there is the incorrect idea that evolution includes within it inherent progress, that evolution is a rising action, always leading to more order. Even really brilliant people, like Ray Kurzweil, the inventor and futurist, betray a lack of understanding in this regard. In this view, evolution is “guided” towards greater and greater complexity. In a chart form, it looks like this, moving from simple to complex:
However, this is not how evolution works. Let’s take natural selection as our example. If a specific adaptation gives an organism a survival advantage, it does so within a specific environment. Since the environment in which a species lives will go through changes, so will the features that provide the greatest advantage. For example, in an environment that is cold, thicker feathers will give a bird an advantage, since the bird can better ward off the chill weather. But, if that environment begins to warm up over time, thicker feathers can become a hindrance, not allowing the bird to cool down properly in the warmer environment. In this case, thinner feathers become the advantageous type of feather. Now, this is an extremely simple example and doesn’t go into trade-offs, but the point is clear. Natural selection does not lead to ever greater order—it simply leads to greater adaptation to the particular environment at that moment in time. In reality then, evolution is not an upward trend over time, always pointing toward progress. Instead, it looks like this:
So, just to recap, evolution is just biological change over time. It does not have any inherent upward trend. It’s a pretty easy concept.
Here’s a great resource if you want to build a good foundation for understanding evolutionary theory: How Humans Evolved – Boyd & Silk. This is the book I used in my biological anthropology class during my undergraduate work. Great stuff.