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David Cowles

Aug 1, 2023

“It may turn out that life is every bit as ubiquitous in the universe as it is on Earth, but it may also turn out that we are utterly alone.”

Ever since I was 5 years old, it has scarcely occurred to me that we might be alone in the Universe. We live in a Universe made up of billions of galaxies, each housing billions of stars. It is ludicrous to think that ‘life’ has occurred just on one insignificant rock in one insignificant solar system in one unremarkable galaxy. 

When my children were still young, we’d spend hours speculating on which moons of which outer planets were most likely to harbor life…and what that life might look like in each case. And Mars? Of course, we’ll find life there; the only question is whether that life will be extant.

For 70 years, the existence of extraterrestrial life was a fixed star in my firmament, a premise of my logos. But that was then!

Now don’t get me wrong, I still believe it is absolutely possible that we will discover incontrovertible evidence – perhaps before I finish this article - that life arose independently somewhere ‘off Earth’. On the other hand, I no longer take for granted such an independent eruption of life.  

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From childhood through middle age, my belief in the existence of extraterrestrial life marked me as a bit of a kook. But over the last 15 years, the rapid discovery of ‘exo-earths’ and the apparent ubiquity of precursor organic compounds has moved public opinion sharply in my direction. Except I’m not there anymore. I’ve moved on. Here’s why:

All life on Earth is a product of the DNA molecule, but that strange double helix appeared only once in Earth’s four billion years history, and that was 3.5 billion years ago. Every single life form on Earth today, every species, every cell is descended from that one DNA molecule. Incredible!

So what’s wrong with this picture? 

  1. It took a mere ½ billion years for the first primitive DNA molecule to synthesize; in the 3.5 billion years since that primordial life event, not a single DNA molecule has formed independently anywhere on Earth. Why not?

  2. If arrangements of organic compounds into molecules other than DNA can manifest the characteristics we label as ‘life’, why haven’t such molecules formed on Earth?

  3. If inorganic elements can synthesize into molecules that manifest the characteristics we label as ‘life’, why hasn’t that happened?

Our study of terrestrial life forms has shown one thing above all else – life is resilient! You can’t kill it, no matter how hard you try. Of course, you can easily kill a single organism with a tug on a trigger. But life itself? No way!  

Consider the evidence. A single DNA molecule is responsible for the 2 million or so ‘known species’ in Earth’s biosphere. (The total number of species may be as many as 10 million.) Even more significantly, life survives virtually everywhere on Earth. It thrives in the Arctic and in the Tropics. It flourishes in water and on land, miles below the oceans’ surface…and miles above. 

Living organisms can breathe oxygen…or carbon dioxide…or methane. Some organisms, like the Water Bear, can apparently survive for extended periods of time (e.g., in outer space) without access to any breathable gas. Freeze an organism for centuries and, under the right conditions, you may be able to revive it. 

The Martian climate, atmosphere, and geology are not particularly hospitable to Earth-like life, but there is no doubt in my mind that terrestrial life forms, once introduced onto Mars, whether naturally or artificially, would survive. Should we not have found evidence of these living organisms by now…if they had ever been there?

Finally, not so very long ago, we doubted the existence of a biological relationship between humans and other species. Later, we accepted that relatedness, but we insisted on supplementing it with some sort of unique ‘spirit’ – soul, élan vital, mind.

Now we know that all life forms are descended from a common ancestor, the primordial DNA molecule. We know that sentience is characteristic of all life forms (even bacteria) and we suspect that we share our crown jewel, consciousness, with a wide range of other species.

Given the self-similarity of all terrestrial life forms, their resilience and their fecundity, it seems that evolution of human-like mental capabilities should not be a one-off event. Intelligent life should exist throughout the Universe; so where is it? 

We’re actively searching (SETI); we’re broadcasting our EM messages into space, but no one is returning our calls. And apparently, nobody is trying to get in touch with us on their own.

The most persuasive argument for the existence of extra-terrestrial life is based on probability theory. It runs like this: “It is infinitesimally probable that life arose once on Earth and not on any of the trillions of satellites orbiting other suns in other galaxies.” 

This argument is persuasive, but entirely fallacious! Suppose I pick a card out of an unknown deck and the card I pick happens to be red. I might be tempted to assume that all cards in the deck are red, and they may be. Or maybe half are red. Or maybe none of the remaining cards is red. Perhaps every card in the deck is a different color. We just don’t know!

We have a single data point. We don’t know if the value of that data point is universal or unique. Without more information, all possible arrangements must be considered equally probable. We need at least one more data point to be able to reason probabilistically; but at the moment, we don’t have that 2nd point. It may turn out that life is every bit as ubiquitous in the Universe as it is on Earth, but it may also turn out that we are utterly alone.


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