But even though Ancient Aliens won't win any logic prizes, there is actually a strong theoretical basis for thinking that aliens may have intervened in earthly evolution. The rationale is not based on direct evidence of such an intervention. It is based instead on probability considerations we can make after analyzing a variety of scenarios relating to the likelihood of intelligent life evolving on a small planet in the habitable zone of a star.
Your basic alien panspermia event
Let's crunch some numbers to throw some light on the issue. Before doing that, I will declare a general intellectual principle worth following: what I may call the principle of improbability minimization. This is the principle that given two explanations, one of which requires us to believe in something with a particular likelihood, and the other requiring a belief in something much more improbable, we should generally prefer the explanation that requires us to believe in the less unlikely occurrence (the event that is not such a huge “long shot”). For example, given the choice between an explanation that requires us to believe in no long shot more unlikely than a 1 in 100 long shot and some other explanation that requires us to believe in a 1 in 1,000,000 long shot, we should minimize the improbability by preferring the explanation that only requires belief in a 1 in 100 long shot.
For example, you notice your lottery playing friend has some additional cash, and you can explain it either by assuming that he won the 3-digit “Daily Numbers” lottery that he regularly plays (with a chance of 1 in 999 of winning), or you can explain it by assuming that he won the Megabucks lottery he also often plays (with a 1 in 1,000,000 chance of winning). Following the principle of improbability minimization, you prefer the first of these two explanations.
Now let's look at different scenarios relating to the likelihood of intelligent life evolving on a small planet like ours, in the habitable zone of a star (the "Goldilocks zone" that is neither too hot nor too cold). The most optimistic possibility is what we can call the “sure thing” hypothesis, which is the assumption that intelligent life will almost always appear on any small planet in a star's habitable zone. If this assumption is correct, then we have absolutely no need to assume that extraterrestrials interfered with evolution on our planet, because such an intervention would have been unnecessary.
But we are far from understanding how the amazing DNA molecule and the language-like genetic code appeared billions of years ago. We also don't understand how natural selection could have produced all the higher human faculties such as inner lives and self-consciousness, as I discuss in this blog post. So it is entirely possible that the probability of intelligent life evolving on a small planet in a habitable zone of a star is very low – perhaps 1 in 1000 or 1 in 100,000 or perhaps as low as 1 in 1,000,000,000,000.
It is under cases like these that the hypothesis of extraterrestrial intervention in earthly evolution becomes very useful. It helps very much in the intellectually desirable goal of improbability minimization. Under some cases, rather than having to believe in a very unlikely event with a probability such as 1 in a 1,000,000, we can believe in a much more probable event with a likelihood such as 1 in 10,000.
Let me give a specific example of what I mean. Let us gloomily suppose that the probability of intelligent life independently evolving on a small planet in the habitable zone is 1 in 1,000,000,000. The number of small planets in the habitable zones of stars in our galaxy is perhaps 10,000,000,000. Under this scenario we would expect that intelligent life would independently evolve on 10 planets in the galaxy. If we don't believe that extraterrestrials interfered in earthly evolution, we have to believe (under this scenario) that our planet lucked out with an event that had a likelihood of only 1 in 1,000,000,000. But imagine we suppose that civilizations on these 10 planets with intelligent life were able to achieve interstellar travel, and that such civilizations (or other civilizations that they helped to make possible) were able to intervene in the evolution of an average of 100 planets, helping intelligent life to evolve on such planets. Then we have a much higher total of planets on which intelligent life appears. In that case the long odds become 100 times shorter. Instead of having to believe in an extremely unlikely 1 in 1,000,000,000 long shot that blessed our planet, we only have to believe in a much less unlikely 1 in 10,000,000 long shot. We have thereby achieved our goal of improbability minimization, and we have made our end assumption much more credible.
The table below shows a range of scenarios concerning the evolution of intelligent life in the galaxy, with each row making a different assumption about how likely it is for intelligent life to independently appear.
Click to Expand
Most rows make the assumption that if intelligent life appears on a planet, that life will travel to other planets and assist in the evolution of intelligent life on other planets (the assumption is that an average of 100 planets will be assisted in such a way). To see the effect of improbability minimization, we can compare columns D and E. In almost all cases the odds in column E are about 100 times greater than the odds in column D. I have adjusted the numbers in cells E10, E11, and E12 to avoid having a probability greater than 1.
This table illustrates the general idea that under many different assumptions about the likelihood of intelligent life evolving on small planets, by assuming the possibility of extraterrestrial intervention in our evolution, we can end up with a less farfetched scenario that requires less of a long shot for it to occur. So contrary to the first impression you may have from watching cheesy shows like Ancient Aliens, the idea of extraterrestrial intervention in earthly evolution would actually seem to be quite respectable from the standpoint of mathematical plausibility (which does not necessarily mean it is likely that such an intervention occurred).
It is interesting to compare the principle of improbability minimization I have evoked here with another worthy intellectual principle: the principle of Occam's Razor, the old and honored principle that “entities should not be multiplied beyond necessity,” or that the simplest explanation is best. Both are good principles, and in many cases both principles lead us to the same conclusion. For example, if I see an ordinary light in the sky, then the principle of improbability minimization leads me to prefer an explanation that the light is an ordinary airplane rather than an alien spacecraft; and the principle of Occam's razor leads me to the same conclusion. But there are some cases in which the two principles may lead us to different conclusions. I may note the very interesting fact that the simplest explanation sometimes has a much lower probability than a more complicated explanation.
For example, suppose a young wife dies of an apparent heart attack in her backyard, apparently from an electrical shock. We can believe she died from a simple lightning bolt, or we can believe she died because of some complicated murder plot hatched by her husband (perhaps because of some fancy electrocuting gadget rigged up by the husband). In this case the principle of Occam's Razor leads us to favor the lightning bolt explanation – it is simpler and also natural. But the principle of improbability minimization leads us to a different answer. Following that principle, we prefer the murder plot explanation, because we wish to avoid believing in the extremely improbable occurrence of a lightning bolt killing the woman.
The question of alien intervention in earthly evolution is another case where the principle of Occam's Razor and the principle of improbability minimization lead us in different directions. The principle of Occam's Razor tends to lead us to shun the idea that any extraterrestrials intervened in earthly evolution, on the grounds that it involves introducing additional entities. But the principle of improbability minimization may lead us to think warmly of such a hypothesis, on the grounds that the overall chance of intelligent life evolving on Earth is much higher if we concede such an evolution may have received external assistance.