Probability, coincidence, and the origin of life

The philosopher Epicurus was shown a wall of pictures — told, reverently, they portrayed sailors who, in storms, prayed to the gods and were saved. “But where,” he asked, “are the pictures of those who prayed and drowned?”

He was exposing the mistake of counting hits and ignoring misses. It’s common when evaluating seemingly paranormal, supernatural, or even miraculous occurrences. Like when some acquaintance appears in a dream and then you learn they’ve just died. Was your dream premonitory? But how often do you dream of people who don’t die? As with Epicurus, this frequently applies to religious “miracles” like answered prayers. We count the hits and ignore the many more unanswered prayers.

I usually work with the radio on. How often do you think I’ll write a word while hearing the same word from the radio? (Not common words, of course, like “like” or “of course.”) In fact it happens regularly, every few days. Spooky? Against astronomical odds? For a particular word, like “particular,” the odds would indeed be very small. But the open-ended case of any word matching is far less improbable. Recently it was “Equatorial Guinea!” Similarly, the odds of any two people’s birthdays matching are about one in 365. But how many must there be in a room before two birthdays likely match? Only 23! This surprises most folks — showing we have shaky intuitions regarding probability and coincidence. Most coincidences are not remarkable at all, but expectable, like my frequent radio matches.

So what does all this have to do with the origin of life? I recently began discussing Dawkins’s book, The Blind Watchmaker, and life’s having (almost certainly) begun with a fairly simple molecular structure, naturally occurring, with the characteristic of self-duplication. Dawkins addresses our intuition that that’s exceedingly improbable.

The essence of evolution by natural selection is, again, small incremental steps over eons of time, each making beneficiaries a bit likelier to survive and reproduce. The replicator molecule utilized by all life is DNA,* which maybe can’t be called “simple” — but Dawkins explains that DNA could itself have evolved in steps, from simpler precursors —non-living ones.

Indeed, non-living replication is familiar to us. That’s how crystals form. They grow by repeating a molecular structure over and over. (I’ve illustrated one we own — trillions of molecules creating a geometrical object with perfectly flat sides.) Dawkins writes of certain naturally occurring clays with similar properties, which could plausibly have been a platform for evolving the more elaborate self-replicators that became life.

Maybe this still seems far-fetched to you. But Dawkins elucidates another key insight relevant here.

Our brains evolved (obviously) to navigate the environment we lived in. Our abilities to conceptualize are tailored accordingly, and don’t extend further (which would have been a waste of biological resources). Thus, explains Dawkins, our intuitive grasp of time is grounded in the spectrum of intervals in our everyday experience — from perhaps a second or so at one end to a century or two at the other. But that’s only a tiny part of the full range, which goes from nanoseconds to billions of years. We didn’t need to grasp those. Likewise, our grasp of sizes runs from perhaps a grain of sand to a mountain. Again, a tiny part of the true spectrum, an atom being vastly smaller, the galaxy vastly larger. Those sizes we never needed to imagine — and so we really can’t.

This applies to all very large (or small) numbers. Our intuitions about probability are similarly circumscribed.

If you could hypothetically travel to early Earth, might you witness life beginning — as I’ve explained it? Of course not. Not in a lifetime. The probability seems so small it feels like zero. And accordingly some people just reject the idea.

Suppose it’s so improbable that it would only occur once in a billion years. But it did have a billion years to happen in! Wherein a one-in-a-billion-year event is hardly unlikely.

The odds against winning the lottery are also astronomical. Our human capacity to grasp such probabilities is, again, so limited that many people play the lottery with no clue about the true smallness of their chances. Yet people win the lottery. And I had my “Equatorial Guinea” coincidence.

And what’s the probability that life did not evolve naturally, along general lines I’ve suggested, but was instead somehow deliberately created by a super-intelligent being of unimaginable power — whose existence in the first place nobody can begin to account for?

Surely zero; a childishly absurd idea. As Sherlock Holmes said, once you eliminate the impossible, whatever remains, howsoever improbable, must be the truth. But the Darwinian naturalistic theory of life is not at all improbable or implausible. There’s tons of evidence for it. And even if there weren’t, Dawkins observes, it would still be the only concept capable of explaining life. Not only is it true, it must be true.

* That all living things use the same DNA code makes it virtually certain that all had a common ancestor. Your forebears were not, actually, monkeys; but the ancestors of all humans, and of all monkeys, were fish.


2 Responses to “Probability, coincidence, and the origin of life”

  1. Josephine Ryan Says:

    Frank, is it possible to get a “share” button on your Rational Optimist posts? From time to time I would like to post your essays on the CDHS face book page and without a button it is difficult to do.




  2. Anonymous Says:

    The existence of evolution is clearly proven by the available scientific evidence. It’s effects are obvious to those who care to look. For instance a new flu virus every year is the result of changes to the virus’ molecular structure. This is an example of what can be properly termed, “micro-evolution.” and it occurs all around us on a daily basis

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