The Genetic Potluck: Why a Diverse Gene Pool is a Good Thing

Figure 1: Example of a gene pool among butterflies

If you have taken a biology or physical/biological anthropology course chances are you have heard the term gene pool (Figure 1).  The idea of a gene pool is a fundamental part of understanding how genes drive or affect evolution and natural selection.  Today’s blog post will delve more deeply into the topic of the gene pool and why having a diverse gene pool is better for a population than having a limited one.

The term gene pool refers to all of the genes available to any given population.  Genes are the building blocks of what we are.  They code for the various features and characteristics of any given organism, thereby determining if someone is color blind or can see in the full spectrum of color, has hitchhikers thumb or not, and can or cannot roll one’s tongue.  While each individual is made up of a series and finite number of genes, a population (a reproductive unit or a group of individuals that can successfully breed with one another) can have a varying number of genes, which is dependent on the number of individuals and the genes they have available in the population. 

What exactly does this mean?  This means that the gene pool of any group is based on the genetic diversity of the individuals within it.  Why does this matter?  It matters because more genetic diversity can be better for the group’s survival.  As noted in the previous post on natural selection there are a series of factors that can affect a group’s ability to survive, but these are all based on the traits present in the individuals who have certain, better (i.e. beneficial for survival) traits or genes.  For example, prior to the Industrial Revolution white moths were better able to survive than black moths because the white moths blended in with their environment better, but black moths were better able to survive during the Industrial Revolution as the soot from the burned coal stained the trees black (Figure 1).  Therefore, the greater the genetic diversity present within the gene pool the greater likelihood that a species will survive regardless of what changes occur through natural selection.  

Figure 2: An example of a potluck meal

Another way to think about this is to consider the gene pool like a potluck meal (Figure 2).  Potluck meals are situations where each individual is expected to bring a different dish in order to provide an assortment of food options.  This allows individuals who have contrasting food preferences (be it out of tastes, allergies, religious beliefs, etc.) the ability to have food available to eat.  The most successful potlucks are those that have at least one dish to meet the diverse needs of everyone at the event, whereas the least successful potlucks will have very few options available.  This would mean that potentially some individuals would go without eating. 

This same idea is applicable to natural selection because the more diversity you have within a gene pool the greater likelihood there is that some members of the group will survive and continue the species on for further generations.  The number of gene choices need to be diverse, containing traits that are seen a preferred as well as those seen as less preferred or potentially harmful because you never know what genes may be beneficial at some point.  This has already been demonstrated in human populations with the genetic mutation of the sickle cell anemia trait.  Sickle cell anemia is a genetic condition that causes the red blood cells, which are typically round, to be sickle shaped.  Round red blood cells can and do successfully transport oxygen throughout the body; sickle cell red blood cells cannot and do not, thereby exhausting the individuals and leading to premature death if the condition is not properly treated.  Why then does the sickle cell anemia trait exist within populations, particularly those whose ancestors come from around the tropical areas (such as around the Mediterranean)?  Because carriers (those who carry one sickle cell anemia gene) are naturally immune to malaria.  Malaria is a parasitic infection transmitted to humans through mosquito bites, and it is a debilitating condition that can and often does kill the infected hosts.  This infection was killing off mass numbers of humans in the past (as well as continues to do so today), so the sickle cell anemia gene was a genetic mutation that allowed for carrier humans to continue to survive and keep the population surviving.  

Ultimately, it is less about individuals and more about the population as a whole surviving.  This is based on the individuals with the strongest/best suited genes at that moment continuing on to keep the population alive.  It does no good, however, if those survivors have a limited number of other genes available in them.  The greater the diversity in their other genes the increased likelihood that if and when another extinction level event or phenomenon occurs the population will continue to survive, and idea that is played out in the fictional example in the recent Netflix film, The Bird Box.  (NOTE: if you have not seen this film and want to stop reading now.)   

The premise of this film is that unseen creatures are wiping out humans.  Humans who manage to see these unseen creatures immediately commit suicide.  Those who are unable to see these creatures are able to survive freely.  Who exactly could that be?  The blind.  The sighted manage to survive by becoming blind, which is done by covering their eyes, but these individuals are disadvantaged because they still rely on their sight so much and have not honed their other senses as well as the blind who can navigate the world successfully without their sight.  This is an excellent example as to how a gene (blindness) that is not preferred can become preferred as the environmental circumstances change (e.g. unseen monsters driving sighted people to kill themselves).