The rationale for genomic SETI is that terrestrial organisms might have been genetically modified or created from scratch by ancient extraterrestrials, and that evidence of this, even deliberate messages, might be found in their genomes.
Hawks notes the similarity to the intelligent design movement, and it reminds me of the UFO religion Raëlism, which claims that all life on Earth was created as an extraterrestrial experiment (there should be a “teach the controversy” t-shirt about that!).
Despite these associations, the idea merits serious consideration. After all, we know that many species already have been modified by human beings, either through selective breeding in the past, or genetic engineering today. These processes leave evidence – genetic and morphological. If aliens exist, they could have done the same.
Davies mentions that a number of unsuccessful searches have been made for signs of an alien message encoded in junk DNA, as far back as 1979. Hawks warns of ‘”Bible Code”-like delusion, but also considers the logistical problems of ensuring that a message could be successfully transmitted:
Consider the difficulty of transmitting a message through DNA over 10 million years. If your DNA “message” is neutral to the organism’s fitness, then the chance it will eventually be fixed in that population is its initial frequency. So, if you want a 50% chance of survival in that population, you’ve got to find and tag 50% of the individuals. Then, you’ve got to pick which populations will survive. Possibly more abundant populations will be more likely to persist, but you’ll have to tag many more individuals in those cases.
I have a copy of Davies’ book, so I can report that the theoretical method of transmitting the message doesn’t require alien visitors to round up entire populations of animals. They don’t even have to leave their home system.
Instead, an extraterrestrial civilization might consider modifying a naturally-occurring nanomachine to convey their message: viruses. Davies writes:
‘A typical virus contains thousands of bits of information encoded in either RNA or DNA – enough for a decent message. So why not engineer trillions of viruses, package them in pea-sized microprobes, and spew them around the galaxy?’
When the viruses encounter a DNA-based cell, they would be programmed to infect them, inserting their message into the germ cells of an organism. ‘Whole chunks of human DNA’, Davies reminds us, ‘are the genomic detritus of ancient viruses that infected our ancestors.’
There are a host of other logistical problems, Davies admits, such as how the aliens would know that life on Earth used DNA to encode biological information. None of the problems are insurmountable, but it got to the point where I wondered if genomic SETI advocates wouldn’t find it easier to simply assume that life on Earth originated through directed panspermia, perhaps with messages included from the beginning.
And in fact Davies does suggest directed panspermia, but for the creation of an artificial ‘shadow biosphere’ of hardy, innocuous and slow-mutating microbes that, as Hawks suggests, ‘differed in some radical way from the rest of life on Earth — different genetic code, lack of common cell machinery like ribosomal RNA, etc.’
Such a population, if discovered, would be a prime place to conduct genetic archaeology.