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Explain xkcd: It's 'cause you're dumb.
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Magic Tree
Since people rarely try to cut down cell phone towers, after millions of years, as cell phone towers have gotten more treelike, trees have started growing fake cell phone tower attachments and shiny gray bark to protect themselves. This is a standard textbook example of convergent evolution.
Title text: Since people rarely try to cut down cell phone towers, after millions of years, as cell phone towers have gotten more treelike, trees have started growing fake cell phone tower attachments and shiny gray bark to protect themselves. This is a standard textbook example of convergent evolution.


Examples of camouflaged cell towers
PalmCellTower.jpg AnotherCellTower.jpg

This comic features a running theme in the xkcd comics, Beret Guy's naive and/or odd ways of thinking. In the beginning of the comic, Beret Guy shows Megan what he believes to be a tree, and explains that it grew there because he placed magic beans in that spot yesterday. This is a reference to the fable "Jack and the Beanstalk", where the protagonist plants several magical beans he acquired, resulting in a beanstalk growing which ascends into the atmosphere. Megan, however, tells Beret Guy that the "tree" is actually a cell phone tower. Beret Guy disagrees, pointing out that it has branches, to which Megan tries to explain that this was in an attempt to make the towers look like trees. She gives up, however, as Beret Guy has already begun climbing the tower.

Later, Megan complains that her cell reception has disappeared. Beret Guy responds by saying that he had to cut down his "tree" because there were "scary giants with yellow helmets" in it. This mirrors, again, the "Jack and the Beanstalk" fable, where the protagonist has to cut down his beanstalk to prevent the giant, whose lands the beanstalk connects to, from climbing down and chasing him. In reality, the "giants" were probably utility workers.

The title text suggests that, over time, trees will evolve to start looking more like cell phone towers in a form of mimicry in order to avoid people cutting them down. Mimicry is where a creature copies the appearance or behavior of another in order to confuse predators. In this scenario, the more defenseless trees attempt to mimic cell phone towers, which have the defense of people not wanting to cut them down or they would lose cell service (and likely a significant amount of money through fines) and because of society's general respect for the the property of others. This is similar to the counting pine, a tree in Terry Pratchett's Discworld series that evolved to display its age with numbers on the outside (in the bark) in the hope that humans would not cut it down and count its rings. Of course now humans hunted it down trying to find a tree with numbers that would fit their house number instead, thus quickly rendering the trees almost completely extinct. (See the tribute to Terry in 1498: Terry Pratchett).

Convergent evolution deals with multiple species acquiring similar characteristics to fulfill their role (such as dolphins and sharks both having a streamlined shape to swim fast) due to the species' common need to adapt to similar environments or tasks. Randall uses the term to describe the convergence in the appearances of cell towers whose design has "evolved" to include tree-like branches and trees which he predicts will evolve to resemble cell phone towers. Each of these "evolutions" would be for the purposes of camouflage, although the cell towers "evolve" by human design for purely aesthetic reasons and the trees would evolve naturally for self-preservation. This would therefore not be a true example of convergent evolution.


[Beret Guy and Megan stand next to a large pole with a note on it. Beret Guy points at the pole.]
Beret Guy: Check it out! I threw my magic beans on the ground here yesterday, and this big tree appeared!
[Zoom out, the pole is revealed to have branches. Around the pole are trees about 1/9th of the height of the pole.]
Megan: That's a cell tower.
Beret Guy: No way - it has branches!
Beret Guy: See?
Beret Guy: I'm gonna climb it!
[Same as frame as the first. Beret Guy starts climbing the pole.]
Megan: No, they just put those there to make it look-
Megan: ...Never mind.
[There is a caption in a small frame inlaid at the top of the last frame:]
[Megan looks at her phone while Beret Guy walks towards her holding an axe.]
Megan: Why do I have no signal?
Beret Guy: There were scary giants with yellow helmets in that tree! Luckily I cut it down before they ate me.

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