[TeMPOraL]

Not that strong. For printer, the shape of a W is an external input. This spider outputs something resembling its own shape. So the question is here, why this and not something else (like randomly shaped clump), and how did it acquire this particular decoy blueprint.

[seiji]

Let me channel dawkins (and/or sagan) for a moment:

Imagine there's a cluster of spiders and a cluster of predators of those spiders. The predators can directly grab the spider, but if it fails and gets caught in the web, the spider wins. The predator is pattern matching on "what looks like a spider."

Maybe a few spider brains create reliable glitches in their webs. Maybe the glitches look enough like not-web where some predators get caught in the web when trying to catch the non-spider. The uneaten spiders-with-web-glitches reproduce and create further glitch making spiders. The predators not caught in the web (i.e. not fooled by the web glitch) also reproduce (n.b. the predators are reproducing glitch-avoiding pattern matching, so we have a glitch-vs-anti-glitch brain race), and some new spiders have more glitchy mutations making bigger anomalies. The anomalies looking more spider like will attract predators, and those spiders won't be eaten as easily. The uneaten spiders can reproduce more glitch-making spiders. The uneaten prey can reproduce more glitch-avoiding prey. The steady state of this model ends up with spiders reproducing themselves so the predator needs more and more advanced web glitch detection. Let this cycle go on for unbelievably long time scales (thousands? tens of thousands? hundreds of thousands? millions of years?), and you have a predator-prey derived "art."

The spider doesn't "know" it's intentionally making decoy spiders. It's just evaluating it's internal tiny spider brain state machine with evolutionarily derived glitches over the past ginormous number of years.

[mkeener]

Yes, Exactly! Another similar example would be the process that produced the heikegani crab.

TL;DR - Over years fishermen threw crabs with face-like patterns on their carapaces back into the ocean. Over time this produced crabs with extremely detailed faces, increasing the chances they wouldn't be eaten and could reproduce.

http://en.wikipedia.org/wiki/Heikegani

[btilly]

If you read your link, you'd find that Carl Sagan's theory is doubtful.

[bonobo]

We often hear about how long mammals' or birds' characteristics took to evolve, I'd like to have a grasp of the scale of time we're dealing with when talking about tiny creatures like these.

I have absolutely no idea of the time that is necessary for such characteristic to evolve, but I think it's not that much time when talking about insects or arachnids. Evolution is not iterated over time, it happens over generations. And when talking about insects or arachnids, we have a lot of them in a short span of time.

[hfsktr]

You raise an interesting topic I've never really given much thought to (time vs generations). Makes me think of other questions about genetics that I just don't know the answers to but that someone must have thought of.

Things like: How do they account for recessive traits? Can something that is recessive become dominant? Can something dominant just disappear (I imagine that it could with mutations happening so much)? Is there a specific animal they use to test these things? Do different traits take longer to evolve towards?

I imagine they use something that reproduces rapidly (fruit flies? fleas?).

On the topic of this spider and how does it know what it looks like...I don't know how much brainpower the spiders have but I know that we have a part of the brain that tracks where our body is (at least in relation to other body parts). Is it possible the spiders have something similar? Can this even be used to make a rough representation of oneself?

I am going to have to google some of these later as I'm now curious.

[glhaynes]

How about a printer with a picture of itself built-in as a test page pattern? :)

I'd guess that its sculptures started as fairly undefined clumps that served the purpose somewhat well (presumably that's what's built by other "sculpting spiders" that the article mentions?). And then evolution has refined that clump, like it does so well.

[ceejayoz]

Natural selection, over millions of years. Slightly more spider-like decoys get selected for.

[popopje]

because one with legs is a more effective decoy? (or whatever other implications a larger spider has)