Monday, January 27, 2014

So What is Evolution?



Probably the biggest reason many dismiss evolution is because most people have no idea what evolution actually is. Evolution is defined as a change in a population over time. 

That's it.

I know. It's that simple. Which is why it is definitely happening. We witness evolution occurring all the time. Any time the genetic makeup of a population varies, evolution is occurring. The question, then, is what is causing evolution to occur.

Typically, there are three main mechanisms that cause evolution. The first is genetic drift. This occurs when a random event changes the population (imagine the difference in a forest after a fire). The second is gene flow - immigration or emigration. Let's say that forest fire caused the rabbits in the area to flee to a new area. That new area just underwent evolution, too. 


The third way evolution can occur is the biggest way. It's called "natural selection." (Image Credit: University of California Museum of Paleontology's Understanding) Natural selection occurs when nature "selects" the next generation by allowing the fit individuals to reproduce in greater numbers than less fit individuals. It's based on a few basic observations (facts, if you will. For more about facts, check out this post). 

1.  Individuals vary within a population. They have different heights, sizes, personalities, skin/coat color, eye colors. Diversity is both wonderful and important.

2. Variation is often heritable. Children tend to look like their parents who look like their parents, and that's because much of who we are and how we look is determined and passed down through DNA. 

3. Competition exists. Not everyone who is born will survive the same amount of time and have the exact same reproductive success. The earth has limited resources, and we all compete for those resources.

4. Some variations lead to greater reproductive success. A particularly fast deer will be able to outrun a predator faster than one who is slower. That individual will likely live longer and thus have more time to produce offspring.

What happens when you put these four facts together? The most successful individuals have the most offspring, and because those successful traits are usually heritable, the next population will have a greater proportion of "successful" traits.

That is natural selection. The population has changed. 

Evolution is often split into two types - "microevolution" and "macroevolution" - and many people will more readily accept microevolution while rejecting macroevolution. Microevolution occurs when there are slight genetic changes occurring in a population over time. If you wait a little longer, to the point when those changes add up to where some individuals can no longer reproduce with other individuals, it becomes macroevolution. Because microevolution and macroevolution are essentially the same thing with a different time frame, this distinction is rather arbitrary and thus accepting one while rejecting the other is fallacious.

People often reject macroevolution because they claim that, because we weren't there to witness it, there's no way to tell what has happened in the past. Apparently, these people also do not believe in forensics and have also never watched CSI, Bones, or Law and Order because we absolutely can test what has happened in the past. We look for clues. We make predictions. We test hypotheses. As a species, we are rather intelligent, rational beings. We can draw conclusions from evidence.

Evolution is based on two big ideas. One is that natural processes that we observe around us today have happened in the past and will continue happening. In other words, the laws of nature are not about to stop (that's sort of what makes them laws). Scientific laws describe behavior, and we've used these laws to harness electricity, to launch satellites, to create atom bombs, to create new drugs.... the list goes on. It is completely logical to assume that laws have always been acting on earth and will continue to act.

The second big idea is that what we find today was caused by something in the past. In other words, effects have causes. If you step outside in the morning and the ground is muddy, you can logically assume that it rained overnight. If you find a whale skeleton on top of a mountain, then at one point, that land was covered by water. 

By putting these two premises together, we can look at what is currently going on and determine what has gone on in the past, and we can draw conclusions about what has caused things that we discover. We look for consistency between cause and effect today and then extend it to cause and effect in the past, and we do the same thing when we study natural phenomena. 

Once we accept these premises, we can begin to make predictions about specific events. We ask ourselves, "If evolution were true, what would we expect to find?" All the evidence for evolution comes from asking ourselves this question and then searching for answers, and each time, the evidence confirms what we would expect to find in a world that evolved. 

Evolution does not mean, "There is no God," nor does it mean, "God didn't create the world." All it says is, "Populations change over time, and given enough time, these changes add up to new species." You can absolutely accept that God created the world and evolution because they are answering different questions: "Who created the world" and "How was that world created." Studying the process by which the Sistine Chapel was painted by no means removes Michelangelo from his creation. It's just looking at it from another perspective.

[1] Eugenie Scott, Evolution vs. Creatoinism, second edition, University of California Press, Berkeley and Los Angeles, xi