Cryptobiology for grownups
There are people who spend their lives searching for Bigfoot, Nessie, or other similarly fictional nonsense. Such people are convinced already that imaginary animals are out there, lurking just out of sight. When asked why they insist on the existence of such strange creatures, for which not a shred of verifiable evidence is ever offered, their responses are typically along the lines of 1) the skeptics are close-minded, and will refuse to accept any form of evidence that contradicts their accepted worldviews, 2) scientists are blind to the real world, caught up as they are in reductionist details, and 3) no one has yet proved that there aren’t any Bigfoots, Nessies, oxygenic photosynethesizers in the late Hadean, etc.
Errors 1) and 2) are a form of psychological projection, apparently, while 3) rests on special pleading and on demands to prove a negative.
On the other hand, there are people who are actually more interested in reality than in promoting a fixed, ideological belief. Using the methods of rational enquiry, acceptance of verifiable evidence, and rejection of failed hypotheses marks the practice of a real scientist. A real scientist comes up with a testable hypothesis, while a poser scientist comes up with a hypothesis impervious to all testing. Hypothetical impenetrability is a sure, dead giveaway of bad science. Good science, on the other hand, offers tests that can be used to disprove even the most cherished hypotheses… rigorous challenges of fact and observation that demonstrate one way or the other if some idea is sound. Bad science never offers such tests, or rejects the failure of a favored hypothesis because to do so would be embarrassing (especially after one has already clung, desperately and loudly, to an overturned idea for decades). Good science accepts when a hypothesis is cast down, and then moves on to the next problem.
A wonderful case in point: the possible existence of a shadow biosphere on Earth. A hypothesis paper just came out in the peer-reviewed journal Astrobiology, in which the authors (Paul Davies at Arizona State University, and co-workers) present not a closed case, but a provocative hypothesis that a “shadow” biosphere composed of unconventional life forms may or may not exist on Earth. Their ideas are provocative, and testable. In fact the paper makes several suggestions about how their proposed ideas could be tested.
What is a shadow biosphere? The idea is basically that multiple independent origins of life could occur on a planet, leading to separate “trees of life” that are structurally divergent and do not share a common ancestor. The concept isn’t as weird as one might think. Earth may or may not have seen the emergence of life multiple times, early in its history, in different regions of the ocean. Life may have arisen in our planet’s primordial seas, only to be obliterated by a world-sterilizing impact. Such impacts were once common, back in the Hadean Eon that brackets our planet’s accretion and chemical differentiation. Many oceans may have rained out to fill the crust’s basins, then were vaporized, then condensed again. For all we know, each time that happened a new and different flavor of life might have started up, only to be annihilated by the next major impact.
Alternately, different incompatible forms of replicator may have arisen in the same stable ocean, but one type was simply more efficient than the others and took over, ultimately pushing their competitors to extinction. But what if the primal competitors didn’t go extinct? What if some of them survived, in geologic settings that are lethal to conventional life? What if bizarre life breeds, even now, in the shadows?
This is an intriguing question, but how could it be tested? Here is the difference between delusion and intellectual honesty: the Davies paper doesn’t assert that a shadow biosphere exists, it asks whether one might exist and how we would test for its presence.
Weird life on Earth might use slightly different compounds, such as a different suite of amino acids. It might use arsenic instead of phosphorus. It might do a lot of things, but whatever it does (or doesn’t do) the results are testable. One example might be unconventional life living deep in hydrothermal vents, at temperatures above 130° C where normal biomolecules all fall apart. It’s possible that a form of life might have evolved early in Earth’s history that uses slightly different kinds of amino compounds from normal life, allowing efficient survival at 130°+ C and high pressure. If so, it’s there and we can detect it by dedicated sampling efforts. We’d be able to isolate bits of such life in the laboratory, tease apart its molecular components, and figure out exactly how it worked. We’d also be able to monitor gases and compounds emitted from high temperature vents, and look for signs of weird biogenic compounds that shouldn’t otherwise be there. We’d be able to design tests that could be failed, in other words.
Davies and co-workers have asked these questions to make people think. They’ve asked whether there might be a shadow biosphere because if there were it would address some very basic questions about the potential for life elsewhere in the universe, and it would allow us to finally figure out whether or not life can only come in one form – ours. Davies and company offer a question, but they don’t assume the answer. That’s science. Davies and company have offered a number of different options for weird life whose existence would be consistent with all other observations about the planet – not just the observations that support their ideas. Davies and company have proposed a bunch of tests that could be carried out, not to prove a negative but to disprove a positive.
One day, when and if all the tests are run and all come out negative, the smart money might no longer support their hypothesis. I’m familiar with the authors’ work, so I expect that even if all the hypotheses presented in their paper are one day shown to be wrong, the authors won’t mind. I suspect they’ll shrug, then move on to the next problem. That’s what separates the grownups from the posers.