It's a Weird Life After All
[My story in the Outlook section, with the usual annotations, linky bits, journalistic detritus and verbal excrescences.]
If we encountered alien life, would we recognize it? I don't mean large, ambulatory, tentacle-snapping organisms with eyeballs on the ends of stalks. Those are always obvious. I'm talking about the low-key, chilled-out microscopic life-forms that might be lurking below the surface of Mars, or beneath the crust of one of Jupiter's jumbo moons, or in some such exotic, slightly scuzzy planetary environment where you'd definitely never find a Starbucks.
What are we looking for, exactly, when we search for alien life? What is life?
[And the corollaries: How much of it is there in our universe? How many habitable worlds are there? How many of them are habitable long enough to allow complex life to evolve? Are there intelligent creatures on other worlds? And if so, where are they? Why don't they respond to our E-vites???]
That's the cosmic question pondered in a new report from the National Research Council, "The Limits of Organic Life in Planetary Systems." For more than five years, a committee of scientists tried to imagine what life-as-we-don't-know-it might be like. The conclusion: Life may exist in forms completely unlike anything we see on Earth. We need to keep our minds open to the possible existence of Weird Life.
You're thinking: Yes, and he works down the street at the video store. But even if this seems a bit silly, it's a big question, and a practical one. Our space program spends billions of dollars trying to figure out where life might be hiding in the solar system. Where do we look? The new report says that, in addition to exploring Mars, we may want to take a closer look at Titan, the huge moon of Saturn where pools of liquid hydrocarbons might contain Weird Life; and Saturn's moon Enceladus, which has geysers of water ice and water vapor shooting through its crust.
Even more provocative is the hypothesis advanced by scientist and author Paul Davies, that there may have been a "second origin" of life on Earth -- or many origins. Weird Life, in fact, may exist right now, on Earth, in what Davies calls a "shadow biosphere." We just haven't figured out how to look for it.
"It could be under our noses, or even in our noses," Davies told me. "The world is teeming with microbes -- squillions and squillions of them. The vast majority of which haven't been characterized, much less had their genome sequenced. We don't know what they are. And some of those might be shadow life."
[More from Davies: "A cubic centimeter of soil typically has billions of organisms. We're swimming in a sea of microorganisms. "We've just begun to probe this vast microscopic biosphere."]
Michael Meyer, lead scientist for NASA's Mars program, agrees: "Our capabilities of looking in the microbial world are still pretty crude. We have marvelously sensitive techniques for finding what we've found before."
Time to take another look under the sofa cushions.
All life as we know it has emerged through Darwinian natural selection. Evolution isn't simply something that happens to life after life gets rolling. NASA's official definition of life is that it's a "self-sustained chemical system capable of undergoing Darwinian evolution." But in the future it may be possible, the new report says, to manipulate human life so that it evolves via Lamarckian, as opposed to Darwinian, processes.
Jean-Baptiste Lamarck was an 18th-century French naturalist and early proponent of the notion of evolution. He proposed the idea, now discredited, of the "inheritance of acquired characteristics," in which attributes and talents gained during one's life could be passed on to one's heirs. Maybe he was just ahead of his time: "Humankind will be able to perceive and solve problems in human biology," the new report reads, "without needing to select among random events, thus sparing the species the need to remove unavoidable genetic defects through the death of individuals."
[In the boodle (see Comments), our resident paleontologist Dooley writes:
'Lamarck deserves a lot more credit than he receives. There are three basic conditions that have to be met in order for evolution to occur:
1) Individuals in a population must vary
2) Variation must be heritable
3) Variation must lead to differential reproductive success
Lamarck actually recognized all of these conditions. His only major mistake was in his understanding of how No. 2 actually worked. He believed, incorrectly, that an organism could pass on to its offspring traits acquired essentially by practice (inheritance of acquired characters). By this idea, condition 2 would be the "active" part of evolution; conditions 1 and 3 would just be a side-effect.
As it turns out, Lamarck was wrong on that point (that's why bodybuilders don't have babies that are born ripped.) Darwin's major contribution was to elevate the importance of No. 3 (natural selection) as the driving force behind the change in a population. That made evolution something that occurs across a population, rather than at the individual level as Lamarck believed....']
[In reporting this piece I had a fascinating interview with evolutionary biologist Sean B. Carroll, author "Endless Forms Most Beautiful." I asked him about the determinism vs. contingency issue: You recall, surely, that Stephen Jay Gould believed that life on Earth was very much a contingent process, a kind of lottery, and that if we were to rewind the tape of life and start anew, we'd be very unlikely to wind up with animals that look like the ones we see today -- including humans. But the counter-argument is that there are reasons why we see the shapes and forms we see. For example, creatures that migrate from land to sea, such as the mammal ancestor of the whale, evolve into more streamlined animals that can move more swiftly through the water. Similarly, the reason that humans have four limbs is that our ancestor was a fish.
"The pectoral and pelvic fins of fish are the forerunners of our forelimbs and hind limbs," Carroll told me. "You don't realize it, but you are four legged. You're a tetrapod. We tetrapods - which include us and salamanders and zebras and turtles - all came from a fish ancestor that had pectoral and pelvic fins."
And my pectoral fins are getting tired from all this typing.]
[For a much better discussion of all this, see my Slate story, "What Do You Say to a Naked Alien?": ["A good argument could be made that a physicist should pose the first batch of questions to an alien, asking whether it's possible to go faster than the speed of light and whether there are other universes outside our own. The physicist and the alien would no doubt get embroiled in a discussion of string theory, and soon they'd be jotting down incomprehensible equations about 10-dimensional vibrating loops. Maybe at the end of the encounter we'd figure out how to yank free energy out of the quantum vacuum. We'd have a new trick for cooking a hot dog."]
Every biologist would love to find even a scrap of extraterrestrial (or weird) life, because right now we have only a single example of biochemistry. We don't know the "rules" of organic chemistry, says John Baross, a University of Washington biologist and the lead author of the report.
[Let's be clear that "weird life" doesn't mean thermophiles found in the geysers at Yellowstone, or the crazy critters found around deep sea vents. Every form of life ever studied on Earth has DNA. Viruses in some cases are just scraps of RNA, but viruses aren't technically alive until they invade a host. There's some thought, I believe, that viruses may be remnants of the "RNA world."]
[Because we don't know how life originated, we don't know if it sparks up rather quickly and routinely or requires a tremendous amount of luck, even given felicitous initial conditions. Christian de Duve is one who argues that life is a "cosmic imperative," that the cosmos is ideally suited for the rise of living things. Davies says of our own planet, "Life did seem to get going rather quickly. Which is a little bit of an indictaor in favor of the cosmic imperative." But even that's not beyond contentious debate. The consensus is that there are microfossils dating back 3.5 billion years, but their biological status has been challenged by one scientist in recent years. For a full knock-down, drag-out account of the Origin of Life (OOL) debate, see the Bob Hazen book "Genesis."]
That said, it's very hard to imagine an organism that wouldn't take advantage of the unusual properties of carbon and water. Carbon is great for making complicated three-dimensional structures -- a protein, say, or a DNA molecule. When we study the universe through telescopes, we see the tell-tale spectroscopic signatures of carbon molecules everywhere. Our cosmos has a hankering to do carbon chemistry. All life on Earth is carbon-based.
Water, meanwhile, is almost a miracle unto itself -- the perfect solvent, with all kinds of quirky properties that help make life possible. In fact, the report turns that statement on its head: Life on Earth uses molecular structures with properties "specifically suited to the demands imposed by water." Water is in charge. And wherever we go on Earth where there's energy and liquid water -- even miles beneath the surface, or around boiling volcanic vents at the bottom of the sea -- we find life.
More important, perhaps, life as we know it has a rather ordinary streak. All living things use mundane elements, the common stuff found all over the place: carbon, hydrogen, nitrogen, oxygen, phosphorous and sulfur. Life is small-d democratic. Maybe a life form could employ exotic elements such as platinum or uranium, but it doesn't seem necessary. Life doesn't have a taste for couture; it buys everything off the rack.
"It is chemical in essence," the report says of life, a statement that is both bland and mind-boggling. Life, you'd think, would be more than just chemicals interacting. Surely it would require some kind of special juice, energy, force. But no: Vitalism is a theory that died out a long time ago. It's just organic chemistry. It's just reactions involving polymers, covalent bonds, catalysts, solvents, nucleophiles, electrophiles.
The report by Baross and his fellow scientists is ultimately optimistic. It's almost a refutation of the "rare earth" hypothesis -- the argument that habitable planets, blessed with the right mix of elements for life and a long time for that life to evolve, are few and far between.
[See the Brownlee/Ward book "Rare Earth," or my own tragically ignored, worst-selling but prepossessingly zesty book Captured By Aliens, which has a chapter entitled "The Mystery Constraint" that limits the abundance of intelligent civilizations:
"Perhaps the Mystery Constraint is a kind of Darwinian law that says that the civilizations that survive and prosper
are the ones that don't call attention to themselves. Maybe there is a cosmic natural selection that favors these circumspect species. If you do blast signals into deep space, you run the risk that you'll be visited by ravenous space predators with mandibles the size of Volkswagens."
There's also a chapter called "The Rules of Life":
"The secret of everything is geometry. The structures have properties. A protein molecule performs its functions not because of any intent or 'power,' but because of how it is folded in three dimensions, and how, in that shape, it fits into various receptors in the body, like a key in a lock. If enough of these properties are in place, and are dynamic in certain ways, we can venture that we're dealing with something that meets our definition of being alive. Life, the exobiologist David Des Marais told me, is 'an emergent characteristic that is fundamentally structural in nature.' By 'emergent' he means that life has no singular cause, like a life force, but is, rather, an overall trait of the system. A good analogy is that, when you get a bunch of water molecules together, you have something that has the property of being wet. No single molecule is even damp...."]
Baross says, "We believe that astrobiology is a science of optimism. We have no idea if life exists elsewhere. We are dedicating our lives to searching for this. Why are we being driven to do this? I think it's such a fundamental question."
Paul Davies reports, "We are still completely in the dark as to whether life is a stupendous chemical fluke that happened once, or whether there is a sort of life principle (or cosmic imperative to use the words of Nobel prizewinner Christian de Duve) at work in the universe. The best (cheapest, easiest) way to settle the debate is to see whether life has started many times over on Earth."
Perhaps the search for life, and Weird Life, offers a good lesson for everyone. We all have a bad habit of tending to see only the things we expect to see. We are innately biased in favor of the familiar. "The human mind finds it difficult to create ideas truly different from what it already knows," the report states.
So look around: Do you see the world as it really is, or as you think it's supposed to be? Can you see -- with your big eyes and big brain -- what's really happening all around you?
Maybe we've found the Weird Life, and it is us.
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