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So I came across something terribly amazing today, that is, a video showing this species of peacock-spider, that literally, transforms into a human face waving his arms about.

What could have possibly given rise to this?

I can understand the arms waving around, but why the uncanny human-face template, complete with eyes, nose, mouth, etc.

I do not believe this to be a case of anthropomorphism on my part, (seeing what I am familiar with), because I cannot imagine any other natural case where such symmetry in a pattern would closely resemble a human face.

Would appreciate any explanation. Thanks!

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I agree with @Alan Boyd, the deaths head hawk moth is another good example. –  relf20 Apr 4 '13 at 21:15
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3 Answers

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I think this really is just a case of what you refer to in your question as anthropomorphism. We are very, very good at seeing faces. Here are some more examples.

Addendum

This site has pictures of quite a few peacock spiders, and as far as I can tell these are all the same species (The only peacock spider mentioned on Wikipedia is Maratus volans).

The remarkable thing about these images is that individual spiders seem to have very different patterns on thorax and abdomen, and many of these are much less like human faces. This seems to me to weaken the case for some sort of mimicry.

Interesting fact: seeing faces and other forms where they do not exist is a psychological phenomenon called pareidolia.

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Im not so sure... I mean, yes, anthropomorphism is a relevant scenario, but some of those faces (like the samurai crab) did evolve due to Japanese fishermen throwing back what they thought looked like crabs with samurai faces, and the solution converged. I am wondering if this face on this spider evolved out of similar feedback with humans and/or other mammals? –  Mohammad Apr 4 '13 at 21:36
    
@Mohammad, I really doubt that the kind of selection that fishermen can provide would be stable enough or even exist over enough time to drive the evolution of such a trait. Even if it were, I find it far more likely that fishermen would chose the crabs that most looked like human faces rather than discard them. –  terdon Apr 5 '13 at 2:39
    
@terdon What about the example with the moths in London who changed their wing color to a darker shade when the industrial revolution covered the city in ashes? I think human activity can provide stable selection in many cases. –  Drosophila Apr 5 '13 at 14:28
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@terdon Absolutely, we do see faces everywhere. But we use a colon and parenthesis because they look like a face. My whole argument is that indeed there's antroporphism, but animals take advantage of that all the time. As for that spider, it is not trying to imitate a human face in particular. Rather, having a back that looks like a scary face may help with larger animals. –  Drosophila Apr 5 '13 at 17:55
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And to note: this is all rather hypothetical, of course. It's hard to get a direct answer to any evolutionary/ecological question, hence there's so much debate. –  Drosophila Apr 5 '13 at 17:57
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In part, the way the spider resembles a human face is due to bilateral symmetry in the body shape and coloring of the spider. Bilateral symmetry evolved early in the animal kingdom to facilitate streamlining of the body (which makes it move faster in any fluid, including air and water), formation of a central nervous system and a head. Human faces (and bodies) are also bilaterally symmetric, hence the resemblance.

Another reason, as you note, is antropomorphism - the ability of humans to see a human face in many natural shapes and colorings. Other animals, including predators probably also have this ability to see faces in nature. This allowed the spider to evolve to imitate a scary face. This is called mimicry and it helps the spider ward off predators.

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Thanks drosophilia. Do you think that in this particular case, this 'face' is used to ward off bigger, (ostensibly animals) who would recognize this as a 'face' of some sort? Or do you think it is just a relic of bilateral symmetry? –  Mohammad Apr 4 '13 at 21:37
    
Not sure. Could be both, I think, since bigger predators may inadvertently crush the spider or use it at play. The scary face could stop them from doing that. –  Drosophila Apr 4 '13 at 21:42
    
The subtitle of the video you linked to says it is a courtship ritual. –  Stockfisch Apr 5 '13 at 10:38
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Peacock spiders certainly aren't mimicking human faces, and I strongly doubt they're mimicking anything at all. As others have noted, it's the combination of a fluke, and some anthropomorphising on your part (easy to do!).

The stunning colours and 'dancing' are actually part of a courtship display, and are most likely under strong sexual selection, rather than selection for any anti-predator function. The male-limited colours are only on display during courtship, and are otherwise flattened along the abdomen. It's also worth remembering that these spiders are tiny (< 5 mm), so the only other animals that are likely to be able to resolve those patterns in any detail are similarly sized organisms with decent eyesight (i.e. female peacock spiders).

Madeline Girard is in the latter-stages of her PhD on these guys, I'd recommend shooting her an e-mail if you're really interested.

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