Colonizing Mars is hard—and genetics is one reason why

Photo credit: NASA

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Imagine for a moment that 20 people were sent from earth to establish a human colony on Mars. From these people, a new society would have to be formed. But what kind of society would it be? What language would the people speak, and what would they look like? From this short thought experiment, you can see that isolating a small batch of people from a larger population can have a dramatic effect on their society—some cultural and physical traits will be overrepresented, while others may even disappear. While this thought experiment may seem to be nothing more than science fiction, it actually demonstrates a concept that has molded populations throughout history. This concept is known as the founder effect.

The founder effect is when a small population of organisms are separated from the larger population, causing some traits to be disproportionately represented relative to the larger population. To understand concepts like this, visualizations can be helpful, so check out the figure below. In this example, you can see how the separation of one group leads to a population that is quite different from the original population that they came from. This concept is important because it helps describe how some populations of humans have developed unique traits—and why some groups have increased rates of certain diseases relative to others.

Iceland is a good example of how the founder effect can change a population. Approximately 1,100 years ago, people emigrated from Scandinavia, Scotland, and Ireland to colonize the island of Iceland [1,2]. Since that initial wave, there has been very little immigration to the island, which means their population of nearly 320,000 people are mostly descended from a small group of ancestors [3]. It is theorized that some people among these early ancestors carried a variant in the BRCA2 gene (for you geneticists, it’s c.771_775del5) [3] that has been passed on and become relatively more common in Iceland than many other populations, which means a higher percentage of Icelanders may be at an increased risk of developing breast and ovarian cancer. In this case, about 1 out of 250 Icelanders is a carrier of this BRCA2 variant, whereas this variant is less common around the world [3,4].

Founder effect vs. bottleneck

The founder effect is very similar to a population bottleneck. In both cases, a group of people from a larger population becomes isolated, but the difference lies in the reason for this isolation.

A bottleneck occurs when there is some catastrophe leading to a large die-off within a population (or at least a large drop in the reproductive pool), such as what happens to the non-resistant bacteria in this video about antibiotic resistance(the survivors make it through the bottleneck).

The founder effect is defined by a group of people becoming isolated, geographically or culturally, and remaining isolated for a period of time.

Increases in rare diseases following the isolation of a group of people have been well studied. A notable example is that of the Fugate family, more commonly known as the “Blue People of Kentucky.” In the early 1800s, a young man moved to an isolated village in Kentucky. This man, Martin Fugate, carried one copy of a rare autosomal recessive variant (meaning the full effects of this variant are not seen unless you have two copies of it, one from each parent) in the CYP5R3 gene [5]. This variant causes a person to have abnormally high levels of methemoglobin, a protein similar to hemoglobin but that is unable to carry oxygen. Too much of this protein can result in low levels of blood and tissue oxygenation, which leads to a bluish hue in the skin—hence the common term for the condition, “blue skin disease.”

Martin Fugate was a carrier of the CYP5R3 variant, and coincidentally, so was his wife Elizabeth Smith [3]. Their community remained isolated for multiple generations. This caused many people in the Fugate family to inherit this variant in the CYP5R3 gene, resulting in high levels of methemoglobin and bluish skin. Once the family dispersed from their isolated community, the rate of blue skin disease decreased significantly [5]. Here the founder effect is apparent: Martin Fugate and his wife were founders. Because they both carried a rare disease variant, and because the family remained isolated, the disease became far more prevalent in their community than it is in the general population [5].

There are many examples of the founder effect, most of which focus on how it has lead to increased disease rates in certain populations. This is because there is a significant medical benefit to society from understanding how diseases are inherited and what genes are involved. However, the founder effect does not only affect disease rates. In the same way that a rare disease can be overrepresented in an isolated population, so too can rare traits such as hair color or skin color. For example, in the Solomon Islands, there is a unique genetic variant affecting hair color that leads to blonde hair in much greater proportions than elsewhere [6].

Isolation of communities can have a profound effect on their culture by limiting their diversity. In terms of genetics, increased genetic diversity helps to prevent rare diseases from becoming common ones. Human history is rich with isolation events, though, which means the founder effect has helped shape the development of some modern cultures.

So what does this mean for establishing a colony on Mars? There will be many hurdles to overcome when voyaging off our planet—radiation exposure, growing food in a sustainable way, the list goes on. And in the long term, these explorers will need to contend with the founder effect, too, which means they’ll need to be resourceful, resilient, and diverse. Is humankind up for the challenge? We think so!

References

1. Helgason, Agnar et al. “Sequences From First Settlers Reveal Rapid Evolution in Icelandic mtDNA Pool.” Ed. Gil McVean. PLoS Genetics 5.1 (2009): e1000343. PMC. Web. 12 Jan. 2018.

2. “Letters from Iceland.” Nature Genetics, 2015, doi:10.1038/ng.3277.

3. Price, Alkes L. et al. “The Impact of Divergence Time on the Nature of Population Structure: An Example from Iceland.” Ed. Gil McVean. PLoS Genetics 5.6 (2009): e1000505. PMC. Web. 12 Jan. 2018.

4. Janavičius, Ramūnas. “Founder BRCA1/2 Mutations in the Europe: Implications for Hereditary Breast-Ovarian Cancer Prevention and Control.” The EPMA Journal 1.3 (2010): 397–412. PMC. Web. 12 Jan. 2018.

5. “Finding The Famous Painting of the Blue People of Kentucky.” DNA Science Blog, PLoS, 22 Sept. 2016, blogs.plos.org/dnascience/2016/09/22/finding-the-famous-painting-of-the-blue-people-of-kentucky/.

6. Sturm, Richard A, and David L Duffy. “Human Pigmentation Genes under Environmental Selection.” Genome Biology 13.9 (2012): 248. PMC. Web. 12 Jan. 2018.