Contagious Diffusion

Distinguishing the different types of cultural diffusion can be tricky and confusing. We can all easily understand what contagious diffusion is, however: think COVID-19. Though that's not a cultural example, viruses serve as a metaphor for the ideas that, like infections, can spread like wildfire from person to person.

Contagious Diffusion Contagious Diffusion

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Table of contents

    Contagious Diffusion Definition

    Cultural mentifacts don't need influencers, the elite, or, indeed, anybody in charge to diffuse.

    Contagious Diffusion is the transfer of culture via mentifacts such as ideas and words that spread laterally (horizontally), like viruses, through human populations, regardless of any hierarchies.

    Contagious Diffusion Diagram

    The easiest way to visualize contagious diffusion is via a dot diagram in which a central dot is the source, and all surrounding dots become "infected" as the mentifact travels away from the source.

    Contagious Diffusion vs Hierarchical Diffusion

    In contagious diffusion, your rank, power, social position, blue check status on Twitter, or any other marker of your cultural standing as an influencer do not matter. You are the same as Elon Musk or Joe Biden—a vector (carrier and transmitter) of a cultural mentifact.

    In hierarchical diffusion, the opposite is true. The people "at the top," by virtue of the way media magnify their voices, become the sources or the intermediate nodes in cultural diffusion. The more cultural influence you have, the more people you can pass the mentifact to. Those at the bottom, in hierarchical diffusion, are simply receivers.

    Consider fashion trends. A famous musician or athlete is paid by a corporation to wear their brand. This idol's millions of young fans purchase the same clothes, an example of hierarchical diffusion. But let's say, instead, that some kids in some high school somewhere invent a new fashion trend. They post what they're wearing to their circle of friends on social media, who post to their circles of friends, and so forth. That's diffusion via contagion.

    Contagious Diffusion vs Contagious Expansion

    There is a lot of confusion regarding the different types of diffusion, so let's get one thing straight: contagious diffusion IS contagious expansion. Let's back up a little, though, to get a better handle on this.

    There are two essential types of cultural diffusion: expansion diffusion and relocation diffusion.

    In reality, most diffusion is a third type, mixed diffusion, which isn't talked about as much in AP Human Geography. What this means is that cultural phenomena diffuse via both relocation AND expansion, in different proportions.

    Relocation diffusion is easy to understand: people relocate and bring their culture with them, "infecting" a new place with their ideas and customs. Meanwhile, their culture might later die out in the old place they relocated from.

    A classic example of relocation diffusion is the Amish and other Anabaptist communities that sprang up in Europe centuries ago. The Amish relocated to the US colonies and beyond, where they have vibrant cultures today. Meanwhile, their culture essentially disappeared in Europe.

    Meanwhile, with expansion diffusion, the cultural traits that diffused remained at their origin as well.

    An example of expansion diffusion is Islam, which spread from the Arabian Peninsula over much of the Old World in the centuries after the Prophet Muhammad's death.

    Three Types of Expansion

    There are three commonly recognized types of expansion diffusion in cultural geography:

    • hierarchical expansion (also known as hierarchical diffusion and hierarchical expansion diffusion)
    • stimulus expansion (also known as stimulus diffusion and stimulus expansion diffusion)
    • contagious expansion (also known as, you guessed it, contagious diffusion and contagious expansion diffusion).

    The differences between contagious and hierarchical diffusion were described above: one is through a "flat" network and one is through a "vertical" hierarchy or network where some people have more power and influence than others.

    Stimulus expansion/diffusion is probably the most confusing, in that it involves changes in the mentifact as it diffuses from place to place and population to population.

    In stimulus expansion, people alter culture to make it palatable for them, like a fast food hamburger from a US chain that changes from beef to soy in a country like India where eating beef is frowned upon or forbidden.

    There is a lot of "diffusion confusion" in AP Human Geography. Useful study aids are the dot diagrams that show the differences between the types of diffusion. Sometimes, an exam question may have a map showing diffusion as well, and ask what type of diffusion is shown, and why it is that type.

    Contagious Diffusion Example

    It's time to recall the difference between mentifact, artifact, and sociofact. These are the three components of culture. All three can diffuse, often together. The mentifact, being the idea or symbol, is at the root of the other two. How does this work?

    Through culture, humans preserve and propagate over space and time certain "cultural identities" with belief systems, values, rules, a vocabulary, and so forth. Culture gives human society meaning and continuity. At the very core of culture are the ideas that guide it, expressed as words, visual images, patterns, and instructions: mentifacts. The mentifacts are incorporated into tangible, material items: artifacts. Meanwhile, sociofacts are institutions such as the family: organizations that provide structure and ways for mentifacts to be preserved and artifacts to be created.

    Let's say you find a piece of ancient red pottery with the image of a crescent moon painted on it using a bluish dye. You have found the artifact of a culture, bearing a mentifact which is the moon image and probably also the color of the pot and dye: all these were significant to the culture that created them. The sociofact, in this case, was likely a social organization such as a religion, a potter's guild, a family workshop, or maybe all three.

    Now let's turn this into a concrete example of contagious diffusion using the Columbian Exchange. And we'll look at maize (corn), the world's most important grain crop.

    The Origins of Corn

    We know that corn is an artifact because it was created through genetic manipulation over thousands of years.

    More than 8,000 years ago, in the Balsas River drainage system of western Mexico in what is now Guerrero state, hunter-gatherers started to tamper with a wild grain we call teosinte (Zea mays ssp. parviglumis) beginning, unbeknownst to them, the creation of modern maize (Zea mays ssp. mays).

    Teosinte (pronounced tay-oh-SINT-ay) is a type of grass you can use for animal forage. It has a small ear and it's not very tasty.

    Contagious diffusion Teosinte StudySmarterFig. 2 - Size difference between the ear of corn's ancestor, teosinte, and a modern ear of corn

    For reasons unknown (given the fact that local people had hundreds of other, more attractive foods to choose from), people in the Balsas began to transplant teosinte and manipulate it by selecting seeds from ears that had the characteristics they wanted.

    They somehow found mutations along the way that transformed the teosinte ear into a tiny maize ear, and over millennia, people selected for larger and larger ears (and many other traits ranging from nutritional value and color to hardiness in different types of weather).

    Maize on the Move

    Long before an ear the size of modern corn had been created, maize spread via contagious diffusion across the Americas. How, and why?

    Maize the artifact had some serious sacred and religious significance, becoming the "flesh" of people in Maya cosmology, and the centrally most important plant in the pre-Columbian Americas. Gods took the shape of maize plants; mythical cultural heroes were said to have been the inventors of maize. Maize imagery is everywhere you look in ancient pottery, stone carvings, and in burials of regular people as well as the elite.

    Maize didn't diffuse at first as an important food crop, though, so why did people carry it with them wherever they went in their migrations and trade routes through the Americas, along with the words for it and the knowledge about how to grow it?

    There are many theories, including:

    • uses by shamans (an ergot fungus that grows on maize is hallucinogenic and may have been used in religious rituals);

    • for the sugar content of its stalks (it was fermented and made into alcohol, something that still occurs);

    • as a relatively minor food item along with many other domesticates, not least among them various types of beans, squashes, tomatoes, and chili peppers.

    For all these reasons and more, maize, beliefs about it, and ways to grow it diffused to the far corners of the Americas, or at least wherever it could be grown.

    Mixed in with contagious diffusion of corn was some hierarchical diffusion and some stimulus diffusion. Once hierarchical societies evolved, you guessed it, they started promoting maize, which took on certain meanings for their elites. Maize gods changed as new nations and states arose, and new uses for maize made it acceptable in places where people might have been resistant to growing it. But maize's diffusion had only just begun!

    Maize Goes Worldwide

    Come 1492, maize was able to take another major jump, this time via relocation diffusion, before it diffused contagiously again.

    Maize popped up in the Old World so quickly in the early 1500s that some scholars have argued that maize existed there before the Columbian voyages (due to maize-like imagery on stone carvings in India, and other evidence). Sticking to classic diffusionism, though, we see that maize, along with chili peppers, potatoes, and other crops, tended to catch on quickly in some regions, was not accepted in others, or didn't become important for a long time.

    Maize was not a sacred crop in the Old World, so it wasn't promoted by rulers and did not spread via hierarchical diffusion. Once in the Old World, it spread via good ol' fashioned contagious diffusion, from market sellers to curious buyers, farmer to farmer, village to village.

    Contagious diffusion Inner mongolia maize StudySmarterFig. 3 - Maize is harvested near Wuhai, Inner Mongolia (China), over 8,000 miles from where it was domesticated

    Why did maize spread to the far corners of the planet? The answer, which is also a major reason it is the number one crop in the world today, is because of how incredibly high its yield is compared to the other grains (wheat, rye, oats, barley, etc.). The number and types of mutations that led from teosinte to corn have never been seen in another domesticated crop, which is why we don't see ears of wheat or ears of rice the size of corncobs!

    The mentifacts involved in the contagious diffusion of corn, once it hit the Old World, weren't that people were the children of maize or the maize gods favored your crop, but rather that maize was this amazing, bountiful plant from which you could produce many different foods (and alcohol!). It was easy to store in a time before refrigeration; it was incredibly nutritious and filling.

    All this and more practical knowledge convinced people that maize was what they wanted to eat and grow. Across Asia, Africa, Europe, and the Pacific, they told or showed their friends and neighbors, and you know the story from there.

    If you are thinking that contagious diffusion in culture involves the best and most useful artifacts that don't NEED influencers or higher-ups to promote them, you'd probably be right!

    Contagious Diffusion - Key takeaways

    • Contagious diffusion is a type of expansion diffusion in which person-to-person contact is the means whereby mentifacts along with the associated artifacts and sociofacts spread across a region.
    • Contagious diffusion involves ideas and knowledge that "catch on" easily because they involve inventions or innovations that people want to adopt, finding them useful and productive.
    • Maize is an example of a cultural artifact that diffused via mentifacts from its place of origin in western Mexico over 9,000 years ago, spreading across the Americas before 1492 and then worldwide.
    • In contagious diffusion, hierarchies are irrelevant.


    1. Fig. 3 Maize in Inner Mongolia ( by Department of Foreign Affairs and Trade ( licensed by CC BY 2.0 (
    Frequently Asked Questions about Contagious Diffusion

    What is contagious diffusion?

    Contagious diffusion is the spread of culture (specifically, mentifacts) from person to person regardless of hierarchy.

    Is social media an example of contagious diffusion?

    Social media incorporates contagious diffusion as well as hierarchical diffusion, as it is a mix between person-to-person spread of ideas and spread by influencers.

    How does contagious diffusion spread?

    Contagious diffusion is the process of spreading from person to person through a space. This happens through conversations, text messages, people making signs and other people reading them, and any other means of direct and indirect communication both in the real world and online.

    What is the difference between relocation diffusion and contagious diffusion?

    Relocation diffusion involves people diffusion culture because they move somewhere, typically meaning that the cultural traits die out in the place they left. In contagious diffusion, people don't move--mentifacts (ideas, memes, etc.) move.

    Is contagious diffusion a type of expansion diffusion?

    Yes, contagious expansion is one of the three types of expansion diffusion.

    Test your knowledge with multiple choice flashcards

    Contagious Diffusion is the same as Stimulus Expansion.

    I migrate from my home in Mali to a small village in Illinois and kids start to copy my hairstyle. This is an example of _______ diffusion followed by _______ diffusion.

    Ideas and words are examples of


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