Monday, June 21, 2010

The Siphon Bearers

A few weeks ago I re-read Stephen Jay Gould's The Flamingo's Smile, essays collected from the mid-1980s, and I was immediately intoxicated by his illumination in one piece on the siphonophores, colonial cnidarians most famously represented by the Portuguese man-o-war. Siphonophores are fascinating in being complex, highly organized colonies that basically function like individuals. Each colony begins as one zooid, with all later zooids budding off asexually and taking specialized forms: floats, swimming bells, feeding siphons (hence "siphonophores," siphon bearers), stinging tentacles, reproductive members. Like other cnidarians, the siphonophore's zooids take the form of either a medusa (like a jellyfish) or a polyp (like a coral individual). These are the two body plans modified to make up the parts of a siphonophore. (Cnidarians in general often have life cycles that involve both medusae and polyps, and both sexual and asexual reproduction. So you can get some sense of the "tool kit" they had that allowed them to evolve this way.)

There's an intriguing question here of whether you call a siphonophore an individual or a group of individuals, and the answer is that it's just ambiguous. Gould develops the specific case in his essay, as always, into a general point: if you perceive a natural paradox, you need to think in terms of a spectrum instead of a set of categories. He lines up by way of example, in order of increasingly ambiguous individuality: ants, aphids, bamboo stands, and then the siphonophores.

Brown University researcher Casey Dunn maintains what appears to be the go-to online introduction to the siphonophores; all of the pages from that left-hand menu are good reading. He states well another fascinating angle to the siphonophores, that they "have become extremely complicated organisms, just as we have, but in an entirely different way. Whereas we are made up of specialized cells that are arranged into tissues and organs, siphonophores are made up of specialized zooids precisely organized at the level of the colony."

Here's a two-minute video from Dunn's lab on the topic, here:

And, from the same source, bioluminescent siphonophore footage with voiceover:

A couple of spookier deep-sea siphonophores can be viewed via YouTube, here and here. And the picture above can be found here. Gould devotes some deserving appreciation to the early-twentieth-century siphonophore illustrations of Ernst Haeckel, some of which can be found at the bottom of the Wikipedia entry.

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Elsewhere in The Flamingo's Smile, Gould writes very eloquently about the prospect of humankind wiping itself out and what kind of a loss that means, even when retaining a modest sense of our being only one aspect of life on Earth. I like this passage a lot, so I'll just quote it at length. . . . If we destroy ourselves
. . . then we have canceled forever the most peculiar and different, unplanned experiment ever generated among the billions of branches [of the tree of life's history] -- the origin, via consciousness, of a twig that could discover its own history and appreciate its continuity.

Some people, who have never extricated themselves from the chain of being, and who view life's history as a tale of linear progress leading predictably to the evolution of consciousness, might be less troubled (in some abstract sense) by our potential self-removal. After all, evolution moves toward complexity and consciousness. If not us, then some other surviving branch will enter the stream and eventually give intelligence a second chance. And if not here, then elsewhere in a populated universe, for nature's laws do not vary from place to place.

As a student of life's history, and as a man who has tried hard to separate cultural prejudice and psychological hope from the story that fossils are trying to tell us, I have reached quite a different conclusion, shared, I think, by most professional colleagues: consciousness is a quirky evolutionary accident, a product of one peculiar lineage that developed most components of intelligence for other evolutionary purposes. If we lose its twig by human extinction, consciousness may not evolve again in any other lineage during the 5 billion years or so left to our earth before the sun explodes. Through no fault of our own, and by dint of no cosmic plan or conscious purpose, we have become, by the power of a glorious evolutionary accident called intelligence, the stewards of life's continuity on earth.
Gould's speaking of nuclear winter here, but you can sense the general application. I've always taken a stance along the lines of "Well, we couldn't eradicate all life even if we tried to, so it wouldn't be the end of the world," but it's true, the stakes are higher than that, like it or not. And I'm always glad to come across well-formed pieces of a non-nihilistic, atheist value system rooted in the appreciation of consciousness and the natural world.


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