Traits that enable organisms to make copies of themselves (i.e. reproduce), or that don't hinder the process, get passed on. Traits that harm an organism's ability to reproduce disappear. That's it. Add to this millions of random mutations and billions of years, and you get a profound diversity of life.
I think a lot of people have trouble grasping the scope of evolution, how you get from a one-celled organism to the complexity of the human body, but the problem lies in our ability to see the entire big picture. It's like trying to conceptualize the distance between the stars. We can throw out numbers with lots of zeros in them, but the human brain can't really relate to it. (For example, do you know it would take over 30 years to count to a billion, if you said one number per second 24 hours a day, every day?) So people have a hard time conceptualizing how a series of accidents can get from something incredibly simple to something amazingly complex.
My point is, we're talking about a LOT OF TIME. So much time that you can't even imagine it with your puny human brain. It's not like a fish gave birth to a dinosaur who gave birth to a monkey who gave birth to your grandparents. There are millions of steps between those things. (And yes, I know we aren't descended from dinosaurs. We aren't descended from monkeys, either, but rather we both came from the same ancestors.)
Another big mistake that people make when trying to understand (or discredit) evolution is that they assume that every part of an organism must have some biological purpose. Nature must have designed it that way. Remember, evolution is all about passing on your genes. Genes that don't hinder that process will still get passed on. Some traits don't necessarily encourage an organism's reproduction, but don't stand in the way of it, either. (I guess they're like Quaker genes.) So they get passed on.
The most fervent argument creationists have against evolution is that so much of the human body appears to be designed by an intelligent being. The watch implies a watchmaker, yadda yadda yadda. But the evidence absolutely does NOT bear this out. There are tons of features in our bodies that appear to have been designed by a crazy person. An intelligent designer would not have given us an appendix, or made our photoreceptors point backwards (causing a blind spot in the human eye), or given us jaws too small for our teeth (leading to wisdom teeth problems), or created a human spine in that location that is under so much weight. These imperfections are much easier explained by accidents of nature than by intelligent design. And that's just one animal. Countless other examples exist throughout the animal kingdom.
Anyway, I dig evolution. I've recently discovered two books that have only intensified my love affair with this biological process.
The first is Michael Pollan's The Botany of Desire. Pollan tells the story of four crops (apples, tulips, marijuana, and potatos) that each represent a different human desire (sweetness, beauty, intoxication, control.) His thesis is that, instead of thinking of agriculture as a way that humans have conquered nature, think of it as a way that plants have used humans to survive. For example, we have cut down forests to plant grains. So the grains have used us to conquer the trees. In the four cases above, the plant took advantage of something that appealed to our human desires to propagate itself. What a fascinating idea!
The latest book is one that I just started reading, Kluge: The Haphazard Construction of the Human Mind by Gary Marcus. He introduces the concept of "kluge" (rhymes with "splooge"), which is an inelegant, inefficient, but effective solution to an engineering problem. Think of Rube Goldberg contests.
Marcus posits that evolution is very klugey, with lots of inefficient forms that work well enough, but don't really look great. (ie. human appendices, eyes, jaws, spines.)
Okay, so I didn't intend to go off on a evolution-inspired rant. (But it felt good nevertheless.) My original intention was to quote a line from Kluge.* First, a little context.
Anyone who knows me knows that I'm not the most kid-friendly uncle around. I've been very ambivalent on the issue of raising youngins. As I get older, I get more interested in my cats than in kids. But lately I've found that a lot of the old hobbies I used to enjoy, like watching TV or playing computer games, just isn't as thrilling as it used to be. I wonder if I'm growing up, ready for a new phase of my life, a new challenge.
Maybe I'm ready to have kids. To finally fulfill my biological purpose: make copies of my genes. Of course, this is a moot point right now, since I would only do this once I found a partner to do it with. But I'm opening myself up to the idea.
So, as I've been ruminating on that thought, I read the following passage in Marcus' book:
Why... do we spend so many hours watching television when it does our genes so little good?
Indeed, I can testify that in my case, TV has done my genes no good whatsoever. I'm not sure how Marcus explains this specifically, since I'm still in the early part of the book, but it is funny to me that he brought up an example that seems to fit so well with my life.
This is my kind of book.
*Not to be confused with Klute, the movie where Jane Fonda plays a prostitute.