Friday, August 31, 2012

30 Second Science: Significant Figures

With some increased traffic to my blog, I'd like to do another "30 Second Science" - a quick post to explain some important or interesting aspect of science. Today we're gonna talk about significant figures.

Now, this is usually a topic that would be covered in a boring chemistry lecture - but it is very important. Significant figures are what determine to what point we can trust a measured value.

An example, grab your calculator. Ok, now: 

\frac{1}{{10}} = 0.1

This is not at all an unexpected result. So if we have one pie and ten people, each person will get one-tenth of the pie. But what if three people were to share four pies?

\frac{4}{3} = 1.33333333333333...
How are those pies to be divided? If we give each person one pie, there will be a whole pie left over. If we give each person 1.3 pies, there will be one-tenth left over. If every person gets 1.33, there will be one one-hundreth left over. If every person gets 1.333, we need a very accurate cutting device and we will still have one one-thousandths of a pie left over!

The answer is obvious, everyone gets about 1.3 pies, and someone gets a little more. This describes significant figures. When we make a scientific measurement, we need to know how many figures (numbers) are important.

A story to drive the point home
I heard this story from a member of my PhD committee. He once attended a lecture of a famous paleontologist. The speaker had brought with him a dinosaur bone. At one point he asked "How old do you think this bone is?"
A woman from the crowd responded "230 million and 5 years old"
"Excuse me," said the speaker, "You are correct, but why 'and 5 years'?"
"Well," the voice called back "I heard you speak five years ago and you said it was 230 million years old. That was five years ago."

I hope you can appreciate the humor in that remark. When the speaker had said it was 230 million years old, he had not meant.
230,000,000 years
but instead simply 230 million years - That is, only 3 significant figures.

Thursday, August 30, 2012

Arguments Against Evolution: What does the science say?

In the next few blog posts I am going to be talking about evolution. I had planned this as one post, but in the end it started getting long - longer than I think any of you would read. So instead I've broken it into two ideas: Responding to arguments against evolution and showing some strong evidence for evolution. Today I'm talking about the first. A later post will address the second.

What is evolution (and what it isn't)
One problem that comes from the evolution debate is a poor understanding of the definition of evolution. A common definition from a dictionary says that:
"A gradual process in which something changes into a different and usually more complex or better form." 
There are a number of errors in that definition. First, an evolutionary change need not be gradual (and what does gradual even mean, scientifically?). Second, evolutionary changes are not required to be more complex. Third, the term "better form" is misleading. Evolution does not happen in a linear fashion with a desired, better end in mind.

A more scientific definition would be:
"Evolution is a process that results in heritable changes in a population spread over many generations."
Many people, I think, don't believe in evolution because they don't understand evolution. They see evolution as an attempt to replace God.1 Their understanding of evolution is that man's ancestors are chimpanzees or some other modern ape.2 That is not what evolution teaches. Evolution also doesn't seek to describe how life originated3. Evolution instead only describes how living things change over time.

I have put together a few of the most common arguments against evolution as well as my answers to those questions.

1. Microevolution vs. Macroevolution
This is probably the number one complaint against evolution that I hear. Often I hear someone say:
"I believe in microevolution, I just don't believe in macroevolution."
To me that sounds like:
"I believe in inches, I just don't believe in miles"
The important difference between microevolution and macroevolution is time - lots and lots of time. The same basic principles govern both processes - mutation, migration, genetic drift, and natural selection. These events over many, many generations result in genetic changes.

Mutation - Mutation is one of the processes responsible for evolution.  Mutations are caused by radiation, viruses, mutagens (chemicals that cause mutations), as well as errors from cell replication. Mutations have been characterized and are known to happen. Imperfections in DNA encoding cannot be denied. 

Migration - Migration is the movement of genes from one population to another. This is an important concept in evolution because gene frequency determines which genes will be passes on.

Genetic Drift - Genetic drift is the change in gene frequency based on random sampling. Genetic drift is more important in smaller populations.

Natural Selection - For some reason, this is the part of evolution that catches some people. If I told you there were two animals - One with a neck 4 feet long and one with a neck 4 feet 6 inches long. Both of these animals must eat from a tree that is 5 feet tall. Which animal will have a better chance of surviving? Of course it is the one with a longer neck. It is just as obvious, then, that if the surviving animal has children it will pass on the genes for height. It's offspring may even have a longer neck making it even easier to survive and pass on even taller genes. 

2. Evolution is "Just at theory"
A word to the wise: If you want to enrage a biology major, the "just a theory" line is a sure way to do it. Here's why - the scientific definition of theory and the colloquial definition are very different. The colloquial definition is an idea that someone has. It can even be a fleeting thought. "I have a theory that..." is a commonly used phrase. The scientific definition is much more rigorous. A theory is not just some idea, it's defined as "a well-substantiated explanation of some aspect of the natural world that can incorporate facts, laws, inferences, and tested hypotheses."
A theory, then, is an explanation of some observation. This explanation must be tested to be correct, provide testable predictions, and is well understood. A theory does not become a fact, no matter how much evidence is given. So when scientists define something as a theory, it means it is well understood, has been tested, and provides testable predictions. Evolution is not "just a theory".

3. Evolution violates the 2nd law of thermodynamics
The second law of thermodynamics, as stated by Lord Kelvin, is that: 
"No process is possible in which the sole result is the absorption of heat from a reservoir and its complete conversion into work."
Now, you may wonder what in the world that statement has to do with evolution. Another, less rigorous definition of the second law is:
"The entropy of a closed system can never decrease"  
I suppose that statement may be as foreign as the first, so let me explain. Entropy, in short, a measurement that describes how energy in a system is arranged. A system where energy is evenly dispersed has higher entropy than a system where energy is unevenly dispersed. Imagine a box with 10 particles. These 10 particles can be arranged in a number of ways.

The box on the left places all the particles at the bottom right, while the box on the right places the particles more evenly throughout. In terms of entropy, the box on the right has a much higher entropy than the box on the left. 

Another, even less rigorous definition of entropy is the amount of disorder of a system. In the boxes example above, the particles on the left are very ordered, while the particles on the right are disordered. The second law of theromdynamics, then, roughly states that a system will always move from the left box to the right - from order to disorder.

And this is what evolution deniers grasp hold on. They claim that since evolution can lead to a more ordered, complex system, that it breaks the second law of thermodynamics. This, of course, is not true. I'll give two reasons: 

1. The second law of thermodynamics states that the entropy of a closed system cannot decrease. Even if we define the system we are looking at as the entire earth, the earth is not a closed system (after all, the sun shines on the earth).  
2. Order and disorder is, in the end,  a poor definition of entropy. It works in many cases to help describe entropy, and it is often correct. However, if you look at the actual definition of the second law it has nothing to do with order or disorder.

There are, of course, other arguments against evolution. I couldn't describe them all in one post. There are also many other misconceptions. In the next blog post I plan on presenting some of the most striking evidence I know for evolution. I'd love to hear your comments about this post until then.


[1] - This is not a topic I plan on addressing in this blog. If you know me and would like to discuss in person I would be more than willing to do that - I look forward to it, in fact.
[2] - This is a common misunderstanding. Evolution does not say man evolved from any modern ape, instead man and modern apes share a common ancestor, which is now extinct. Saying man descended from a chimpanzee, or any other modern ape, is like saying you descended from your cousin.
[3] - This is one reason why I don't understand how creation is seen as the opposite of evolution. Evolutionary biologists aren't interested in how life originated. That is an entirely different field of science.

Check out part 2 here. Also, don't forget to like us on Facebook and follow on Twitter.