6. Are Intelligent Aliens a Threat to Humanity? Diseases (Viruses, Bacteria) From Space. Chandra Wickramasinghe, Ph.D., Centre for Astrobiology, Cardiff University, UK

On the panspermia hypothesis the genetic components that led to life on Earth are omnipresent in the galaxy, so the same or similar genes that arrived here would also arrive at the surfaces of other planets (Hoyle and Wickramasinghe, 1982; Joseph, 2009; Joseph and Schild 2010). Every niche in every habitable planet in the galaxy would then be colonized with unity probability thus leading to the widespread occurrence of microbial life. The fraction that eventually evolves into higher life is debatable, but with identical genetic structures delivered to a multitude of similar environments and planetary niches self-similar patterns of evolution and a convergence of evolution could be expected. In terrestrial life for instance, the evolution of the eye is achieved independently at least thrice. Intelligence of the kind humans process may be argued to have some measure of survival advantage in that a greater capacity to understand our environment would lead to greater skills at manipulating it to our advantage. On this basis high levels of intelligence could be understood as a cosmic evolutionary imperative. It is also unwise to regard ourselves – homo sapiens sapiens – as the culmination of this evolutionary process. With just a million years or so of human evolution towards it would seem that the experiment of intelligence has scarcely begun on Earth. Thus creatures endowed with higher levels of intelligence could well be commonplace in the Universe.

Let us next estimate the number of habitable planets in our Galaxy. With about 500 exoplanets discovered thus far mostly within ~ 30 pc of us, it would be reasonable to conjecture that about 25% of main sequence stars are endowed with planets. Most of the planets that have been observed, however, are of Jupiter mass, and a large fraction orbit stars in a binary pair. It is difficult to estimate the number of planets that are in non-binary systems and therefore in stable orbits. It is only in such cases that one could expect evolution that leads to higher life and eventually intelligence. At a reasonable guess one might expect to find billion such planets corresponding to – 1% of main sequence stars.

The number of planets N carrying intelligent life in the Galaxy could now be derived from a simplified form of Drake’s equation:

Here n is the total number of habitable planets in the galaxy, L is the average lifetime in years of an intelligent civilization, and t is the main sequence age of a star. With t ≈ 5 x 10⁹ yr and n ≈ 10⁹ we then have

The prospects for visitations from ETI, benign or otherwise, depends on the value of L we choose for the lifetime of intelligent or superintelligent life on a planet. An upper limit would of course be defined by a main sequence lifetime, ~ 10⁹ yr, but more realistically it will be shorter. Our human experience on Earth over the past century does not give much confidence in choosing much higher values of L than say 500 yr. In this case we have N = 100 as the steady-state grand total of advanced intelligent civilizations throughout the galaxy. Such pessimism is based on the simple fact that today’s nuclear arsenals of the world have enough fire power to extinguish all life on the planet, and it is difficult to imagine that this would not be an eventual outcome of unbridled human greed for power and control. However, if the next stage in the evolution of intelligence is to adopt a strategy of non-violent co-existence, then it could be that L will be much higher. For argument’s sake, taking L to have an optimistically high value of ~10⁸ years, the number of planets endowed with intelligent life becomes 2x10⁷ and their mean separation in the galactic disc ~ 10pc. If we are thinking of space-faring intelligent aliens being optimistically able to travel at a tenth of the speed of light, the average crossing time between adjacent civilizations will be ~ 300yr.

If one now considers the expansion of a single power-hungry civilization, colonization might proceed in an expanding wavefront across the set of habitable planets as shown in Fig. 1. If to the crossing time (at one tenth the speed of light) of 300 years we add a recuperation time of say ~ 700 years, each step in the expanding wavefront would take ~ 1000 years, and to cross the entire galaxy would take a few million years. (This is a variant of the argument used earlier by Enrico Fermi to argue that if intelligent life exists elsewhere we should have been colonized already.) This argument, however, is based on the assumption that the behavior of superintelligent space colonizers could be modeled on predator-prey relationships found in lower life on the Earth, as well as on the history of our own colonization and conquest of more primitive tribes.

Even with the most favourable set of assumptions the model is suspect however. With the numerical values chosen in this example, our space colonisers would need to have biological generation time (mean life-span) considerably in excess of ours. Otherwise, we have to posit that the potential predator embarks on a space voyage that benefits not its own generation but several generations into the future. No example exists on Earth where this model applies, either naturally in the living world, or in a sociological context. Indeed our modern politicians find it difficult to plan for the well-being of society beyond even a few electoral terms of office!

Colonisation of a galaxy via the process of directed panspermia (Crick and Orgel, 1973) offers a much better prospect. An advanced technological civilization facing the prospect of imminent extinction may well decide to package its genetic heritage within microbes, including viruses, and launch them out into space. They might even consider targeting comets of their own planetary system as a first staging post, where gene packages might become amplified in vast numbers. The spread across the galaxy would then be greatly facilitated. No expensive rocket system is needed. The genetic packages are of the right sizes for their propulsion by the radiation pressure of starlight to be guaranteed (Wickramasinghe and Wickramasinghe, 2003; Wickramasinghe, Wickramasinghe & Napier, 2010). Although a large fraction of such space travelling genes will perish in transit, the reassembly of surviving genes on habitable planets would lead indirectly to galactic colonization.

The real risk to humanity of alien life may be in the form of viral and bacterial genomes arriving at the Earth which are sometimes pathogenic (Joseph and Wickramasinghe 2010). Fred Hoyle and the present author have argued the thesis of “Diseases from Space” over several decades (Hoyle and Wickramasinghe, 1979, 1982, 1990; Hoyle et al, 1985; Wickramasinghe et al, 2003). Despite criticisms that have often been made against this concept the basic arguments remain cogent to the present day (Joseph and Wickramasinghe 2010). With increasing evidence to support the view that life could not have arisen indigenously on the Earth, the idea that the evolution of life is modulated by genes arriving from comets has acquired a new significance. Darwinian evolution operates in an open system where new genes continue to be added from a cosmic source. Pandemics of viral and bacterial disease become an inevitable part of this thesis. One could argue that if not for such genetic additions from outside, evolution would have come to a standstill a long time ago (Hoyle and Wickramasinghe, 1982; Joseph and Wickramasinghe 2010). In this context it should be noted that the human genome has recently been found to contain more than 50 percent of its content in the form of well defined inert viral genes. It is possible to understand this data if our ancestral line of descent over a few million years had suffered a succession of near-culling events following outbreaks of viral pandemics (Joseph and Wickramasinghe 2010). On each such occasion only a small breeding group survived the members of which had assimilated the virus into their reproductive line.

Expanding wavefront of galactic colonisation.

Hoyle and the present author have cited numerous instances from the history of medicine where outbreaks of pandemic disease could be elegantly explained in terms of space incident viruses. Even the modern scourge of influenza is likely to be driven by periodic injections of genetic components from space. Aspects of the epidemiology of influenza otherwise remains difficult to explain (Hoyle and Wickramasinghe, 1979, 1991).

In conclusion, we note that the aliens we have to fear are not superintelligent creatures arriving in space ships and intending to conquer and subdue us, but sub-micron sized viral invaders that may threaten the very existence of our species.

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