Random vs. Stochastic Evolution

In most conversations about evolution, the words “random” and “stochastic” are used interchangeably. They are entirely different.

“Random” means absence of pattern and purpose.

“Stochastic” means:

The word stochastic in English was originally used as an adjective with the definition “pertaining to conjecturing”, and stemming from a Greek word meaning “to aim at a mark, guess”, and the Oxford English Dictionary gives the year 1662 as its earliest occurrence. (Wikipedia)

This conveys the flavor that “stochastic” carries in engineering, where there’s an entire field called Stochastic Control Systems.

A Southwest Airlines 737 flying from Boston to Baltimore is a stochastic control system. The wind is a random variable and the flight path is the goal.

The control system adjusts in response to random variables (wind) in order to land in Baltimore.

The plane’s control system aims at a mark, makes a guess, and corrects as it goes.

Random vs. Stochastic is not arcane quibbling about semantics. It is essential to accurately model evolution.

In Darwinian evolution, mutations were always traditionally assumed to be random; the only correction, or aim, is supplied by natural selection.

When my brother confronted me with this question in 2004, I thought, “In engineering I have never seen a system that is optimized only by replication, variation and selection. It always has some controlling or correcting mechanism.”

Was I wrong? Did the biologists know something I didn’t know? I guessed I might harbor all manner of erroneous notions. I was entirely willing to turn my worldview upside down if this was really true.

I discovered a bevy of error correction, editing, and adaptive systems employed by cells. Evolution is not driven by copying errors or “randomness” in the usual sense. Cells evolve because the cell is a stochastic control system that modifies its own genome in pursuit of its goals.

The real question is: Just how purposeful is this behavior? Denis Noble raised this question in his paper “Was the Watchmaker Blind? Or Was She One-Eyed?”

Noble doesn’t attempt an answer… but he does cite many examples of organisms adapting to the needs of threatening situations. In real time.

We don’t know how purposeful or directional evolution is. What do know is: In systems we do understand, like drones, computers, prosthetic arms, thermostats and guided missiles, “replication + random mutation + selection” are never sufficient to evolve any technology.

If replication + mutation + selection evolved technology, Genetic Algorithms would be all the rage in Silicon Valley. They are occasionally useful.

In his Algorithm Design Manual, Steven Skiena warns against genetic algorithms:

    [I]t is quite unnatural to model applications in terms of genetic operators like mutation and crossover on bit strings. The pseudobiology adds another level of complexity between you and your problem. Second, genetic algorithms take a very long time on nontrivial problems. […] [T]he analogy with evolution—where significant progress requires millions of years—can be quite appropriate.

    I have never encountered any problem where genetic algorithms seemed to me the right way to attack it. Further, I have never seen any computational results reported using genetic algorithms that have favorably impressed me. Stick to simulated annealing for your heuristic search voodoo needs.

    — Steven Skiena

30 years of engineering  are more than enough to convince me that evolutionary theorists are missing something very big (huge – massiveas big as Einstein’s theories) when they toss around words like random… and then refuse to define what they mean.

Eyes and ears and wings don’t emerge because chunks of DNA get randomly shuffled like a deck of cards. Something vastly more sophisticated is going on… right under our nose. Intelligent Design theorists are missing the same landmark discovery when they abdicate to “God did it.” Sure, I believe in God… but the true science has been bulldozed by both sides.

In her 1984 Nobel Prize paper, Barbara McClintock asked: What does a cell know about itself? This is one of the most profound and provocative questions in all of science. Even fragmentary answers promise great breakthroughs in medicine and technology.

We won’t get answers until we use precise language to describe evolution. It’s time to separate the signal from the noise.

By Anthony92931 [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)], from Wikimedia Commons

By Abmcdonald (talk) (Uploads) – Own work, CC BY 3.0, https://en.wikipedia.org/w/index.php?curid=22507293

6 Responses

  1. Michael Champion says:

    “A Southwest Airlines 737 flying from Boston to Baltimore is a stochastic control system. The wind is a random variable and the flight path is the goal.”
    From this you can summarize the entire article in two bullet points.
    Random=undirected, chaotic, accumulation of passive random effects
    Stochastic=Directed towards a goal, ordered, compensates for random factors and removes them

    Meaning stochastic is the exact opposite of random. The terms used just make it go over most people’s heads if they are glancing at it.

    • Michael,

      Yes, in the field of Stochastic Control Systems, which is a very thoroughly developed branch of engineering (drones / missiles / HVAC systems / self driving cars etc) it does mean nearly the exact opposite of random.

      BTW I have a stack of blog comments from you. Will get to them. Has been an incredibly busy couple of months. Which has been good from my end, but sorry they’re still sitting there.

  2. Mark Chenoweth says:


    I couldn’t really tell from this podcast from Jeff Zweerink if this discovery he was talking about would apply to the Evolution 2.0 prize. Maybe you can elaborate on whether creating quantum life is akin to understanding the origin of life?


    • Mark,

      The discovery wouldn’t win the prize, as they had to model it on a very sophisticated computer that someone had to build; whereas we’re looking for someone to generate code from chemicals as an emergent property. But I do believe it is very much a related concept. In my personal opinion a cell is a quantum computer, and we do know that photosynthesis for example harnesses quantum tunneling as a means of increasing the efficiency of energy production.

      I think we have decent reasons to suspect that quantum phenomena are at the heart of the behavior of living things and that to think of biology as purely Newtonian is an assumption that will someday be shown to be obsolete.

      I think that evolution, gene editing, quantum computing and AI are on a collision course, as all of the above invoke related principles.

      Very interesting, thanks for calling this to my attention.

  3. Ours might have been the 10²³rd (or a trillion times over) big bang that ever happened. In fact, there may have been an endless number of big bangs preceding the one that eventually produced mindful observers. We would not know how many times randomness has led to chaos that produced only noise. Nobody would know because there was nobody there to observe it. Time appears to only exist when observers are present.
    The whole concept of noise and signal needs an observer that tries to draw meaning from the various states of his/her nervous system, calling some aspects signal, the rest noise. The world may fail to be impressed by this distinction just like the stones in my garden don’t care if I own them. There is a similarity here with Ralph Waldo Emerson’s statement about weeds (noise) in the garden (signal): “What is a weed? A plant whose virtues have not yet been discovered.”
    Belief in God is not knowledge. It doesn’t have to be. It neither is a halfwit’s whim. Belief is the assumption that something is true because you have good reasons to think so. Talking about God is a different matter again. It borders on the impossible to even try to describe what you mean when you say “God” because communication and consciousness are limited and God is not. The limited cannot hold the unlimited.
    If nothing more, belief in God is a healthy choice. We cannot know for certain but a sense of purpose and direction in my life (and in the world) feels right to me. There would be less room for spiritual growth if there were irrefutable proof of God’s existence and the true properties of such an entity. Because I cannot know, I have to probe deeper and deeper as I go, struggling for balance and feeling the more alive for it.

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