On Tuesday I began discussing the questions Kieran Healy posed about the ability of a future intelligent species detecting our involvement in producing the mosaic genomes of geneticall modified organisms that might survive after we and any evidence of our existence is gone. He asked whether internal evidence derived from the sequences would allow this future species to infer our existence.
Using the example of the genetic mosaicism within our own cells – the distant evolutionary relationship pf mitochondrial and nuclear genomes and the transfer of many mitochondrial genes to the nuclear genome – I concluded that these future scientists (a) would certainly be able to recognize the mosaic origin of of any GMOs that survived, (b) would certainly argue a lot about the mechanisms that could produce such mosaics, and (c) would certainly not take the gene shuffling they found as evidence that we existed.
Why not? Click through for my explanation.
Think about how science works. The explanations scientist provide for phenomena are based on empirical generalizations. We explain the sun's “rise” every morning as part of a larger theory about the structure of the solar system and the motion of planets. A key aspect of such generalizations in science is that they apply to a wide range of phenomena. Our understanding of the solar system's structure allows us not only to eplain why the sun “rises” every morning, but why we have solar and lunar eclipses. Combined our understanding of gravity, our understanding of the solar system allows us to predict tides with great accuracy.
Now think about the situation we've postulated. By hypothesis all other evidence of our civilization has been erased. The only set of phenomena that postulating our existence would allow these future scientists to explain is the weird relationships of genes in a few organisms. Were they to postulate our existence as the explanation for these phenomena – their empirical generalization – they'd be right, but their generalization wouldn't allow them to predict any new phenomena and it wouldn't provide a logical connection to other phenomena that were unexplained. It would be like postulating that objects fall to earth when released not only because of earth's gravitational attraction, but because their are little homunculi embedded within every object that just happen to guide the motion of those objects in accordance with the generalizations of physics. In both cases, postulating the existence of some agency that acts in accordance with established empirical principles is consistent with the data, but the postulates are not scientific postulates. By hypothesis, there is no way to test their validity.
So future scientists could describe the pattern of evolutionary relationships among genes in GMOs and recognize that horizontal gene transfer was involved in their ancestry. They could argue about a variety of plausible mechanisms that might have caused the transfer. As empirical scientists, however, they could not postulate the existence of an “intelligent designer” – us – in the absence of other evidence of our existence. Other theories they put forward to explain the horizontal gene transfer would be wrong, but they would also be the only empirically testable alternatives, the only scientific hypotheses available.
In short, scientific knowledge is limited in two important senses:
Scientific generalizations are always subject to revision. No matter how well supported, no matter how extensively tested, no matter how extensively applied, new observations can always lead to the revision of currently accepted ideas. Scientific knowledge is limited in the sense that we can never be certain that scientific generalizations are true.
Scientific generalizations are incomplete. Scientific generalizations describe observable phenomena1 in terms of processes that can be observed. This means that scientific generalizations may be wrong (as they would be in our example above), but to discover that they are wrong we would have to have access to non-empirical knowledge, knowledge outside the realm of science. Scientific knowledge is limited in the sense that it is limited to observable phenomena and processes.
1Note to philosophers: I'm using “observable phenomenon” very broadly here to mean any phenomenon that can be empirically verified, even if that verification involves a very long chain of inference. I regard quarks as observable, for example.
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