Are aliens little green men of unpredictable motives? Horrible insect-like face-hugging, chest-exploding monsters? Are they super-smart, super-slimy, super-fishy, body-cavity-probing, disc-flying creatures, searching for planets to colonize and people to destroy as Stephen Hawking warned, or are they something much more mundane? Could there be alien life already on earth, too microscopic, too different to notice? Could life on earth have been seeded from an alien land, with secret messages encoded in our DNA? We’ve been scanning the sky for extraterrestrial radio signals for years, should we have been scanning the earth for chemical traces of alien life instead? As Stephen Hawking said, “the numbers alone make thinking about aliens perfectly rational,” so let’s think a little about aliens and the search for alien organisms on earth.
A recent New York Times article asks if there are aliens already living on earth and we just haven’t been looking hard enough to find it. In this case, alien doesn’t necessarily mean this other life is from another planet, but the existence of a different form of life on earth would point to a higher possibility of a different kind of life starting up somewhere else. All life found on earth uses DNA and other common metabolic currencies, rooting the tree of life to a single common ancestor. If life arose multiple times, only our DNA-life won–unless there is a second biosphere that we just haven’t found yet:
The denizens of the hidden “alien” biosphere — let’s call them Life 2.0 — might employ radically different biochemical processes than the life we know and love. Microbiologists could easily have overlooked their existence, because their methods are focused on the biochemistry of standard life. Obviously, if you go looking for A, you will find A and not B.
There is a small group of scientists called astrobiologists now searching extreme environments on earth for clues about alien life. They search hot springs, undersea volcanic vents, and other inhospitable (except to some extreme but otherwise “normal” organisms) environments in search of organisms with different metabolisms, microbes that use arsenic instead of phosphorous or microbes that use mirror-image versions of common metabolites. If different kinds of life can coexist on one planet, each adapted to their own extreme niche or even sharing a single ecosystem, the prospects for life on other planets becomes magnified.
Others have suggested that not only could there be other alien forms of life on earth, but that all life on earth was seeded by an alien race, our nearest common ancestor landing on earth on a meteorite or dropped off by a spaceship. This concept, called panspermia, is not a new idea, but has been more recently advocated by the renowned biologist Francis Crick, who wrote a paper in 1973 hypothesizing about the kind of spaceship that would have brought life to earth, piloted by an alien race seeking out planets to terraform and replace their own dying planetary ecosystem (PDF).
Later that same decade, as molecular biology and sequencing technology improved, others investigated whether DNA sequences of earth organisms held encoded messages from aliens (ok, you would think that Francis Crick writing about spaceships would be the craziest part of this post but this is where the “rational” part of “thinking about aliens” really breaks down). Nick pointed me to an interesting article written in 1979 asking “Is bacteriophage φX174 DNA a message from an extraterrestrial intelligence?” The authors hypothesized that super-smart aliens could have sent messages to us in the form of a virus that infects one of the bacterial species common in our gut (E. coli). They noticed that one of the few proteins encoded by the phage genome had 121 amino acids, and as this is the square of 11–a prime number–they tried to decode the protein sequence into a binary color system looking for recognizable shapes in the 2D grid (the figure on the right shows a few attempts).
As they conclude in the article: “Unfortunately, no significant pattern was observed on the arrays so far examined. However further speculation is irresistible.” Could our DNA really be a message from space? Could we someday encode messages to aliens in DNA that we leave behind somewhere else? Perhaps the most interesting and prescient aspect of this wacky study is the idea that sometime soon after it was written it would be possible for humans to synthesize large swaths of DNA and encode whatever messages we want in it. Already scientists have synthesized the genomes of viruses and bacteria, with the synthesizers’ “signature” encoded as part of the sequence. Others are taking this idea even further–experimental poet Christian Bök (who first tweeted the link to the alien phage article) is working on a poem encoded into a synthetic strand of DNA. Perhaps someday in the future super-smart aliens will find these sequences and learn a little bit about us.