By Otis F. Graf Jr.
A fisherman grabs his net with a rather large mesh size and heads for his favorite lake. After a day of fishing, he notices that his entire catch is larger than six inches. He concludes, therefore, that there are no fish smaller than six inches in the lake. This is an example of observer selection bias where the fisherman arrives at a false conclusion by not accounting for the design of his net.
Part 2 of this series (see part 1 here) will explain how observer selection bias, where a sample obtained is not representative of the population, also affects astrobiologists studying extremophiles. We will consider its impact on the conclusions they draw from their research, and see what our knowledge of extremophiles really tells us about the likelihood of life on extraterrestrial bodies.
Discovery of Extremophiles Is an Observer Selection Effect
In 1983, theoretical physicist Brandon Carter warned of the biases that can arise in science when we ignore the unique conditions for our existence:
In making general inferences from what we observe in the Universe, we must allow for the fact that our observations are inevitably biased by selection effects arising from the restriction that our situation should satisfy the conditions that are necessary a priori, for our existence. 1
Astrobiologists have been vulnerable to the observer selection effect in this way: If it were not for the fantastic adaptability of the unique type of life that emerged on Earth and transformed the planet, we would not be here to observe it.
Figure 1: Marble Earth. The uniquely adaptable life that emerged on Earth transformed the planet into a home for intelligent observers. Image credit: NASA
From the evidence of Earth’s extremophiles, we can draw two important conclusions: (1) Life on Earth originated under special and unique conditions, and (2) Earth life is extremely adaptable. The adaptability of that original and unique DNA/RNA/carbon-based family of cells cannot be overemphasized because without it and the enormous biomass and biodiversity that resulted from it, we would not be here. During the previous few billion years, Earth’s enormous variety of organisms has converted a water-shrouded rock into a living planet that has all the ingredients to support our technological civilization.
One important example of such adaptable life is sulfate-reducing bacteria (SRB). These vital organisms converted soluble metals into high-grade metal ores in the Earth’s crust. It took about 2 billion years, but without diverse and abundant SRB, metallurgy and our technological capabilities would not exist.2 Without that technology, in turn, we would not know that extremophiles exist. In this immense spectrum of interrelated and interdependent life and nonlife, the tiny set of constituents identified as Earth’s extremophiles are there because all the rest are there; and we would not be here if all the rest were not there.
The observer selection bias comes into play when we realize we are here and extremophiles are here for the reason that unique DNA/RNA/carbon-based life emerged on Earth about 4 billion years ago. Thus, extremophiles are no more surprising than all the other complex forms of life on Earth, including all the plants and animals. They tell us little about what we should expect to find on extraterrestrial bodies beyond Earth. So what do they tell us?
Extremophiles as Evidence against Widespread Life
Contrary to conventional wisdom, Earth’s extremophiles stand as evidence against life being common and widespread in the galaxy. First, it must be acknowledged that scientists still have scant clues as to how life emerged on Earth. In the words of physicist and astrobiologist Paul Davies, “We are almost as much in the dark today about the pathway from non-life to life as Darwin [was].” 3
Second, as discussed in Part 1, all the evidence indicates that life emerged only once on our planet during its 4.5-billion-year history. This observation leads to the obvious conclusion that the emergence of life is an extremely improbable event. As Davies has noted, “If life really does pop up readily, then it should have started many times on our home planet.”4 There is no evidence of another emergence of life on Earth and much evidence against it, including that from extremophiles. We can reasonably conclude from what scientists have learned in the extensive study of extremophiles that, as Davies suspected, life in the cosmos is rare after all.
Evidence Points to Creation
The unity of Earth’s entire biomass, including extremophiles, is not what would be expected from undirected natural processes. Instead, the unity of biochemical design and information processing across all of life on Earth appears to be the hallmark of the work of a single creative mind. Just as an artist uses a distinctive style to identify his or her paintings,5 the Creator of the universe has left his “watermark,” so it seems, on all the works of his hands. Extremophiles are yet another example of the many scientific discoveries that validate the authority of the Bible.
Finally, it is difficult (perhaps impossible) to imagine a natural explanation of an event that occurred only once on a planet in 4 billion years. That one-time event is indistinguishable from a miracle. If we evaluate the evidence from what is known of extremophiles and all other forms of life on Earth, two conclusions follow: (1) the emergence of life from nonlife in our galaxy is, and would be, an extremely improbable and rare event, and (2) the best explanation of its existence, wherever it is found, is that it is the work of the God of the Bible.