I’m sure you’ve heard before that no two individuals have identical DNA (even identical twins), however, individuals from the same area have more similar genomes than those geographically separated. This makes sense as mating becomes less random and more common between individuals closest to one another (a bird wouldn’t fly miles away to mate if a viable mate was near by). This means that genes reflect geography, social practices, and even customs, and all of these factors cause the categories we know as race, ethnicity, and customs (kind of a chicken or the egg scenario). In fact, many studies have examined this very idea of physical/social/temporal restrictions causing categories within the human population. This infographic comes from a paper where the researchers took DNA samples from many individuals around Europe and found that genetic similarities and differences correlated with geographic position. As you can see the green dots (mostly representing Eastern Europe) and much further away from the dots representing Southern Europe (Italy, Spain, etc.).
This was one of the first studies to examine this trend in humans, however, we’ve been witnessing this idea of population stratification in nature for hundreds of years, it’s usually called ‘speciation’. There are two main flavors of speciation: allopatric (when a population is split into two by geographic separation and evolves separately to become two separate species) and sympatric (when a population is not split geographically, but two species are still produced due to behavioral or social differences). There are also peripatric and parapatric speciation, but those two are just so fun we should save them for a different post.
Okay, so… trees are pretty cool… But you know what’s cooler? Dystopian films. One of the most popular series right now is the Divergent Trilogy which is the story of a run down (well, more run down) city of Chicago 200 years in the future. The city is now divided up into five factions all based on personality traits: Dauntless (the brave), Amity (the peaceful), Erudite (the intelligent), Abnegation (the selfless), and Candor (the honest). You may want to stop now if you’re sensitive to spoilers…
It is revealed that the city of Chicago was isolated from the rest of the United States as a genetic experiment (if you want to read more details on this look here: https://en.wikipedia.org/wiki/Allegiant_(novel)) to attempt to increase the numbers of divergent individuals.
This makes the Divergent universe a great way to explain speciation (and makes it WAY different than the Hunger Games universe, you haters). For example, the people of Chicago and the people outside of Chicago have had 200 years to undergo (slight) allopatric speciation as they are geographically separated and all mating between them has stopped. Perhaps the people outside Chicago will have different allele frequencies of blue eyes, or increased disease tolerance than those people inside, they will most likely still be able to produce viable offspring, so they will not be different species, but if Tris Prior had been born 1,000 years later who knows what could have happened.
Additionally, inside Chicago there are the five factions which represent five unique groups that have distinct behavioral and social customs which restrict random mating between the different factions. Though some individuals change factions, become factionless, or are divergent, this is rare which makes the gene flow between these five communities limited. For example: someone who is dauntless is more likely to mate with another dauntless who has similar attributes (bravery, toughness, in prime physical condition) than someone from Erudite who values intelligence and can barely run. This suggests that the factions themselves are on the path of becoming separate species from one another if only there was more time.