February 12th, 2009 was Charles Darwin’s 200th birthday. That weekend, I had dinner with some friends, most of whom are scientists. I mentioned Darwin’s birthday and, being scientists, we raised our glasses and toasted Darwin. However, one of the ladies at the table, who is not a scientist, objected and said that evolution is just a theory and she doesn’t believe it. She was the only person at the table to hold this opinion, and much of the night was spent trying to convince her otherwise. Her primary stumbling block was her belief that evolution is an entirely random process, and she did not believe that ever-increasing complexity could arise by chance. There are a variety of things wrong with her idea of evolution, and what I quickly realized is that she simply did not understand evolution. Worse yet, I quickly learned that a table full of scientists could not do a sufficient job of explaining it to her! This led me to ask myself a couple of questions. First of all, how many people out there accept evolution without fully understanding it? Secondly, how many people do not believe in evolution because they simply do not understand it? Therefore, I decided to write this blog post as a simple introduction to evolution. Universities offer entire courses focused on explaining evolution. This post is not meant to substitute for a 4-month college class. Instead, I simply aim to address the basics of evolution and some of the common misconceptions.
In 1859, 150 years ago, Charles Darwin published On the Origin of Species, one of the most important and influential books ever written. In it, Darwin introduced his theory of evolution, which itself evolved over the course of Darwin’s 5 year journey around the world on the HMS Beagle, and in the subsequent years studying his notes from the journey. At its core, Darwin’s theory established a scientific explanation for diversity in nature. A minimal working definition of evolution is “a process that results in heritable changes in a population spread over many generations.”
Webster’s dictionary defines evolution as, “the development of a species, organism, or organ from its original or primitive state to its present or specialized state; phylogeny or ontogeny.” Definitions such as this one are inaccurate for a number of reasons. First, they imply that modern species/organisms/organs arose in their present form from original or primitive species/organisms/organs. This leads to anti-evolutionists saying things like, “I didn’t evolve from a monkey!” They are absolutely right! They did not evolve from a monkey. The primary problem with such definitions is that they ignore the most important parts of evolution, thus leading to a great deal of confusion. It is absolutely necessary to underscore the point that evolution is a gradual process, “spread over many generations.” It is absolutely necessary to point out that evolution “results in heritable changes,” meaning that the changes are genetic and can be passed from one generation to the next. Finally, it is imperative to point out that evolution applies to entire populations, not individuals.
Such inaccurate, but widely touted, definitions have given rise to many misconceptions of evolution. Many of these misconceptions have been dealt with elsewhere, and I encourage the reader to continue learning about this process by exploring the links and Related Articles section below. While I may be accused of oversimplification, I will now attempt to address a few of the most common misconceptions of evolution.
First of all, I will address my friend’s belief that evolution is entirely random. In fact, evolution may be considered a two-step process. It is true that there is some degree of randomness. The first step of evolution is the introduction of genetic mutations, which occur by chance or randomness. However, mutations constantly arise and the vast majority of mutations are lost. For a mutation to take hold and be passed on to subsequent generations, it must provide some advantage. This is part of the process of natural selection, or the second step of evolution. Natural selection is tightly regulated by the environment, and is anything but random.
That being said, natural selection is only a piece of the puzzle. If we ignore chance events, we are ignoring a large part of the process of evolution. As I said, mutations are constantly occurring, due to a multitude of factors. In fact, every human embryo contains at least 100 new mutations. Some of these mutations may be harmful and may be lost during natural selection, often resulting in death of the embryo. However, most mutations are neutral, meaning they provide no positive or negative influence. When a mutation is beneficial and passed along, or is harmful and lost, that is natural selection. If a mutation is neutral and is passed along, as will happen simply because there are so many neutral mutations, that is an example of random genetic drift. A specific example of genetic drift in a population is eye color. Humans, and other diploid organisms, have two copies (alleles) for each gene. In the case of eye color, if a person has brown eyes, they may have a brown allele and a blue allele, but brown is dominant and will be expressed while blue is recessive and not expressed. However, either the brown or blue allele can be passed on to offspring, creating the possibility that two brown-eyed parents can have blue-eyed offspring. In effect, genes of offspring are a random sampling of parental genes.
Another misconception voiced by my friend is that evolution leads to ever-increasing complexity. It is certainly true that evolution has produced a multitude of complex organisms, including humans, and this complexity is due in part to natural selection. However, recent research has led to a competing hypothesis, suggesting that increased complexity actually results when selection is weak or absent. In essence, this hypothesis suggests that weak selection may allow for things such as duplicate copies of genes, which may arise due to genetic drift and be weeded out when selection is strong. For instance, there is a great deal of evidence that some modern, “simple” species have actually evolved from more complex ancestors. Examples include many species of cavefish and other organisms that live in the murky depths of the ocean, which have lost their eyes due to natural selection. Living constantly in darkness, these organisms no longer needed their eyes. As other traits gradually evolved to aid survival in darkness, unnecessary features such as eyes gradually disappeared, illustrating that evolution giveth, and evolution taketh away.
Counter to the above misconception, many people also believe that evolution is unlikely to produce complexity. This view is often the result of the failure to understand the time necessary to produce complex organisms, and is another example of the confusion that can arise from inadequate definitions of evolution. It is true that a single mutation, or even a series of mutations, is unlikely to produce more complex organisms. But more complex organisms do not typically arise in a single generation. The evolution of complex organisms requires multiple generations. Life on earth, as we know it, has evolved over billions of years. The process has involved countless mutations, many of which have been positively selected, and many more of which have been eliminated. It is important to remember that natural selection is not intrinsically progressive, meaning it does not tend toward more complex organisms. Populations are selected for either increased or decreased complexity in response to local environmental conditions.
Another misconception is that natural selection always promotes the survival of species. In fact, natural selection applies not only to populations of organisms, but also to genes. While it may be difficult to comprehend, positive selection of genes can actually be detrimental to the whole organism. Examples include transposons, which are positively selected DNA elements that can cause genetic diseases such as hemophilia. Multiple other examples exist and are given a more thorough treatment here. It is important to note that evolution is not always a constructive process. While we are surrounded by examples of successful species, countless others have failed, resulting in extinction of species.
The last thing I would like to address is the teaching of evolution in this country. Much of the rest of the developed world accepts evolution more than the United States. To some degree, this is likely the result of religious influence. It is no surprise that the more devout a person, the less likely they are to believe in evolution. These beliefs have a tremendous influence on our politics and, thus, our education system. Therefore, the treatment of evolution in our schools is often meager, at best, and many states continue to push the teaching of intelligent design/creationism as a realistic alternative. The map below is from a 2002 Scientific American article and illustrates how and where evolution is taught in the US.
As you can see, as recently as 2002 only a handful of states received “Very good/excellent” ratings. For the record, I received a pretty good science education in a North Carolina public school, including the teaching of evolution. I distinctly remember that one of my favorite biology teachers, while teaching evolution, was asked by another student if she believed in God. The teacher said she did, but chose to believe evolution was God’s plan. That teacher was an example of someone who found a balance between her religious views and her scientific views. She did not let her religious beliefs mar her scientific views, and she did a good job of teaching evolution. Many other students are not so lucky.
There are those who argue that evolution is just a theory and has not, or even cannot be, proved, so should not be taught. In fact, evolution is supported by overwhelming evidence that has accumulated over billions of years. As a virologist, I see evolution on practically a daily basis. In fact, you can watch the process of evolution almost daily in any microbiology laboratory in the world. Viruses and bacteria, as examples, are constantly evolving. The process of natural selection leads to drug-resistant bacteria and the new strains of influenza virus we see every year, which make us create a new flu vaccine every year.
There are also those who say that it doesn’t matter whether or not we accept evolution. Believe it or not, evolution impacts our lives. People who do not understand, or choose to deny, the mountains of scientific evidence supporting evolution are all too often the people making decisions that affect the rest of us. A rejection of evolution is a rejection of basic science principles. These principles have shaped not only our country, but the entire world. To reject these principles is to deny our history, and to impede our future.
While this post is intended to be a simplified overview of evolution, I want it to be as accurate as possible. There are far too many inaccurate accounts out there, and this should not be yet another one. Therefore, if you believe that I have left out something particularly important, or that I have not given a proper treatment to any of the topics, please let me know in the comments. Similarly, if you would like additional clarification on anything I have written here, please do not hesitate to ask questions in the comments. This blog is, above all, a place for education.
- Evolution: 24 Myths and Misconceptions
- Understanding Evolution
- What is the evidence for evolution?
- July 1, 1858: Darwin and Wallace Shift the Paradigm
- New Findings Confirm Darwin’s Theory: Evolution Not Random
- New Insights into the Evolution of the Human Genome
- Fossils Challenge Old Evolution Theory
- Out Of Africa — Bacteria, As Well: Homo Sapiens And H. Pylori Jointly Spread Across The Globe
- Study Detects Recent Instance of Human Evolution
- 12 Elegant Examples of Evolution
- Darwin still making waves 200 years later
- Darwin 200 years: Things you didn’t know about Charles Darwin
- At 200, Darwin Evolves Beyond Evolution
- The Human Pedigree: A Timeline of Hominid Evolution
- The Future of Man–How Will Evolution Change Humans?
- Putting Evolution to Use in the Everyday World