Evolution: Project De-mythification

One of the major differences between the theory of evolution and other major scientific theories is that almost everybody thinks they understand it. However, dissemination of public discussion and personal opinion about any scientific theory can result in widespread misconceptions, inevitably arising due to a lack of proper knowledge about a given theory.  The theory of evolution has been particularly vulnerable to uniformed public debate. Although the average person would most likely not discuss quantum or relativity theories with families and friends, evolution is a topic considered somehow more approachable.
In this column, I will discuss the theory of evolution by pointing to and dispelling different myths and/or misconceptions surrounding it.
To begin, I would like to discuss the mechanisms of evolution. For you, the reader, the term “natural selection” may immediately come to your mind. Yet, natural selection is only one mechanism of evolution. Let us go a bit slower and take a closer look at what exactly natural selection is.
First, imagine a population with its individuals bearing inheritable traits. Second, imagine that some of these traits might increase the chance of the individuals exhibiting it to produce more offspring. Third, imagine that there is a limitation of one or more resources that does not allow all of the individuals of the population to produce offspring to the maximum of their capacity – so, the population is either growing slower than its maximum capacity or staying more or less at the same number in the subsequent generations. Therefore, logically we expect the individuals that have the traits that give them higher chances of producing offspring to have more offspring in the next generation. As a result, in the following generation, the frequency of these traits in the population will increase. In other words, these traits are favored, or selected by the nature.
The change in the frequency of the inheritable traits from one generation to the other is called evolution. This is the very core definition of evolution. In the example above, evolution was caused by natural selection. But other forces can also alter frequency of inheritable traits in the population and thus cause the population to evolve. Consider in the same example above, what if none of the traits give their owners a higher chance in having more offspring? Are the frequencies of the traits going to stay the same as this generation? If all of the individuals have equal (or more realistic close to equal) chances of having offspring, then the frequency of the traits in the next generation is dependent on the current generation’s frequencies and luck! In other words, frequencies can vary from generation to generation (i.e. population can evolve) randomly or by a process called genetic drift.
In real populations, genetic drift and natural selection are two of the main mechanisms of evolution. They can be strong or weak, depending on many factors. One of the important factors in determining the power of these forces is the size of the population. For example, in a population of 10,000 rabbits, the ones that have longer ears (that might make them more alert to the predator), with a frequency of as low as 1%, still comprise 100 rabbits. Because these rabbits have lower chances of being eaten by their predators, they can produce more offspring. So little by little and generation by generation, the frequency of long-ear rabbits increases. On the other hand, in the population of the foxes that hunt on these rabbits, which might be about 100 individuals, a trait that enables them see a little better in the dark with the same frequency (1%) could comprise of only one or two foxes and they might not even get the chance to mate and produce offspring. In this scenario, the trait might even be lost in the next generation. To put it in a nutshell, genetic drift is a more powerful evolutionary force in smaller populations. This means that in those smaller populations, the frequencies tend to vary more randomly. In contrast, natural selection is a more powerful mechanism in the evolution of larger populations.
In the next issue, I will provide more examples about the effect of natural selection in opposition to genetic drift and will also introduce yet another mechanism of evolution named migration.

Copyright Iris