In his book Darwin's Doubt, Stephen C. Meyer calls our attention to an unexplained anomaly in paleontology. When we examine the fossil record, we don't see fossils appearing in larger and larger sizes, at an even rate of progression between 3 billion years ago and 100 million years ago. Instead, we see relatively little fossil evidence of life prior to the Cambrian era about 500 million years ago. But during the Cambrian era there is a sudden surge of fossils in the fossil record. This sudden blossoming of life during the Cambrian era is known as the Cambrian explosion. The Cambrian explosion is illustrated in the diagram below, from a paper suggesting a prosaic explanation for it. The "known fossil range" lines go back no further than the Cambrian era.
Meyer (who has a PhD from the University of Cambridge) argues that this Cambrian explosion is the result of intelligent design at work in the evolution of life. But there is an alternative to assuming a supernatural hand at work in such a thing. Maybe the Cambrian explosion was caused by extraterrestrials.
We can imagine a hypothetical conversation that could have occurred millions of years ago, aboard an alien spaceship that entered into orbit around our planet.
Xynus: So give me the facts. What is the status of life on this planet?
Zeesin: Our underwater robot probes have confirmed that this planet is an evolutionary dud. There's hardly anything here in the way of life. What a waste of time coming here to this crummy little rock! I told you we should have checked out Alpha Centauri instead.
Xynus: But maybe we can turn this “dud” into a success. What if we were to accelerate the evolution of life on this planet? Maybe we can turn a dull planet into something where intelligence might eventually evolve.
Zeesin: What do you have in mind? Finding some of those dismal organisms in this planet's oceans, and then gene-splicing them to soup up their evolution? That would be a pretty hard chore. You know I don't like to get my four feet wet.
Xynus: No, I have something very different in mind. We can create some species ourselves using our nanotechnology biology lab. We need merely specify some requirements, and the computer will take care of designing the appropriate DNA. We can print out the organisms cell layer by cell layer using our molecular materializer. Then we just dump the newly designed organisms into the oceans of this planet.
Zeesin: Okay, I guess there's nothing much else to do around here.
There are three ages in time when the idea of extraterrestrial intervention might be helpful. The first is the point when the most primitive life developed. Modern science has not yet explained a plausible scenario by which that occurred, partially because of the difficulty of explaining both the origin of a self-replicating molecule and the difficulty of explaining the origin of the genetic code. The second age in time is the Cambrian explosion mentioned here. The third age in time is the time when we saw the emergence of human intelligence. We might call this the “consciousness explosion,” when man seemed to gain in a relatively short span of time (geologically speaking) a variety of subtle mental characteristics such as aesthetic abilities, spirituality, math abilities, language abilities, musical abilities, introspection, and moral reasoning. Accounting for this consciousness explosion is perhaps more difficult than accounting for the Cambrian explosion, given that most of these things are not easy to explain through natural selection, as they are mostly not traits that increase an organism's likelihood of surviving until reproduction.
But there is a barrier to anyone suggesting that some design – either extraterrestrial or supernatural – may have played some role in the origin of life or earthly life or human life. Some scientists have declared that any mention of design in discussing such matters is “not part of science” or “unscientific.” This thought taboo is indefensible. A few examples show very clearly that there is no truth to the idea that “scientists don't consider the possibility of design” when trying to consider causes.
For example, imagine a strange radio signal is received from deep space. If the signal is sufficiently suspicious, a scientist will indeed consider the hypothesis that design was involved, and that the signal may be a signal from an extraterrestrial civilization. Or imagine that some suspicious looking structure (on an asteroid, moon, or planet) is photographed by a space probe. A scientist will indeed consider the hypothesis that design was involved, and that the structure may have been designed by some extraterrestrial expedition that arrived in our solar system. Or suppose a scientist finds some artificial-looking object buried in a geological bed. A scientist will indeed consider the hypothesis that design was involved, and that the structure may have been designed by some human or some extraterrestrial visitor. Any scientist could advance any of these ideas in a scientific paper without fear of being excluded because he had considered some possibility of design.
The notion, therefore, that considering (or arguing for) a possibility of design in discussing the origins of life on earth is unscientific (or not admissible in a science publication) makes no sense. Such claims need to be translated. When a scientist claims that a hypothesis is “not part of science,” what he typically means is that such a hypothesis “is forbidden or should be forbidden to scientists.” When he claims that a particular hypothesis is unscientific, what he typically means is that such a hypothesis is a taboo that violates the tribal norms of the scientific community. Such claims tell us about sociological and cultural restrictions and prohibitions within the scientific community, but usually don't give us any cogent principle as to how our thought should be limited.