Whatever the rigor of the Fermi paradox, there have been many solutions proposed for it. The challenge to most of these solutions is the large-number assertion: while this or that explanation might explain the failure of some, even most, civilizations to colonize the galaxy, the timescale for colonization is putatively so short that unless the total number of civilizations in galactic history were quite small, the galaxy would indeed have been colonized. These colonization scenarios have posited exponential reproduction and paid little attention to ecological factors, such as the evolution of predation or other behavior that could have the effect of reducing the rate of expansion of a space-faring population. What parameters does one choose in predator-prey modeling to depict accurately the expansion timescales of competing technical civilizations? It is hard to make such parameter choices with a feeling of confidence. And it is close to impossible to know whether such simple analogies from life on Earth are or are not applicable.
Various practical arguments against galactic spaceflight being commonplace have been countered by invoking either genetic engineering or artificial intelligence in the form of self-replicating and evolving machines. We should not exaggerate the ease or casualness with which substantial genetic manipulation of human beings will be done, but as Robert Carlson has shown, basic measures of human bioengineering power, such as the time or cost required to sequence or synthesize short sequences of DNA, show that biotechnology is exponentially advancing at a rate even faster than that of Moore’s law in computing. It is hard to know what comes after this exponential lift-off. It may prove generally true that there is only a brief interval during which a species is technically intelligent yet still retains its biologically evolved form. If so, we should expect that any civilization with which we make contact through SETI or otherwise is unlikely to resemble its biological predecessor species. If the question is “what will they look like?” the answer may be “whatever they want to.”
But well before biotechnology permits the reengineering of the human species, it will put great power for extremely dangerous manipulations of microorganisms into the hands of small groups of the technically competent. Indeed, it is doing so already. (The National Academies has already convened two committees to examine this issue.) We do not have adequate models from Cold War arms control or nuclear nonproliferation for how to manage this new world, gaining the benefits of biotechnology for public health and food security while preventing disaster. The same technological expertise that makes possible our increasingly sophisticated searches for life brings with it powerful new opportunities, if mishandled, for destruction. Astrobiology is defined as “the study of the living universe.” If so, then the discipline must also speak to the future of human civilization, a thing uniquely precious regardless of whether it is entirely alone or one of many in the galaxy.