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The Other Unsolved Problem of Evolution

Photo credit: ModelTMitch, CC BY-SA 4.0 , via Wikimedia Commons.

It is generally accepted that the main problem with Darwin’s explanation for evolution is the existence of many apparently “irreducibly complex” features in living things, and especially in their cells. How could these features evolve gradually through apparently useless intermediate stages? In a 2020 Evolution News post I offered one spectacular example: the aquatic bladderworts, whose carnivorous traps have

trigger hairs attached to a valve-like door which normally keeps the trap tightly closed. The sides of the trap are compressed under tension, but when a small form of animal life touches one of the trigger hairs the valve opens, the bladder suddenly expands, and the animal is sucked into the trap.

Wolf-Ekkehard Lӧnnig and Heinz-Albert Becker, in their article on carnivorous plants that is quoted in the post, write that 

it appears to be hard even to imagine clearcut selective advantages for all the thousands of postulated intermediate steps in a gradual scenario…for the origin of the complex carnivorous plant structures examined above.

A More Fundamental Difficulty

How plants could gradually evolve water-tight traps with valve-like doors and trigger hairs is a very difficult problem. But a recent article of mine, “Human-Engineered Self-Replicating Machines,” focuses on a more fundamental problem: we really have no idea how living things are able to pass their current complex structures on to their descendants generation after generation, without significant degradation — much less how they evolve even more complex structures.

The new peer-reviewed article in the journal BioCosmos explains why human engineers are not close to building self-replicating machines and argues that “we are unlikely to be successful in explaining how the self-replicating machines we see everywhere in the living world could have arisen through entirely natural causes, when we still do not know how such machines could be designed.”

The Problem of Self-Replicating Machines

A few paragraphs from the new article:

With all our advanced technology, we are not close to producing human-engineered self-replicating machines. This is significant because it is widely believed that the first self-replicators on Earth must have arisen through chance chemical processes — it being impossible to appeal to natural selection of replication errors before anything could self-replicate. 

To better appreciate the enormous difficulties in designing such machines, and thus the difficulties in understanding how the first living things arose on Earth, let’s think about what would be required to build, say, a self-replicating “Model T” car.

We know how to build a simple Model T. Now let’s build a factory inside this car, so that it can produce Model T cars automatically, and call the new car, with the Model T factory inside, a “Model U.” A car with an entire automobile factory inside, which never requires any human intervention, is far beyond our current technology, but it doesn’t seem impossible that future generations might be able to build a Model U.

Of course, the Model U cars are not self-replicators, because they can only construct simple Model T’s. So let’s add more technology to this car so that it can build Model U’s, that is, Model T’s with car-building factories inside. This new “Model V” car, with a fully automated factory inside capable of producing Model U’s (which are themselves far beyond our current technology) would be unthinkably complex. But is this new Model V now a self-replicator? No, because it only builds the much simpler Model U. The Model V species will become extinct after two generations, because their children will be Model U’s, and their grandchildren will be infertile Model T’s. 

So back to work, and each time we add technology to this car, to move it closer to the goal of reproduction, we only move the goalposts, because now we have a more complicated car to reproduce. It seems that the new models would grow exponentially in complexity. And even if we were able to engineer self-replicating cars, it is hard to imagine that without any human maintenance these cars could keep reproducing themselves for more than a few generations before errors accumulate to the point that all replication halts.

And here we have ignored the very difficult question of where these cars get the raw materials they need to supply their factories. 

Some will object here that the first living things may have been much simpler than self-replicating cars. It is widely believed that you only need to explain how very simple self-replicators could have arisen though chance chemical processes, because then natural selection of the resulting duplication errors could take over and explain how self-replicators far more complex than cars could have arisen. But even if we could explain the appearance of simple self-replicators, imagining trying to design self-replicating cars may help us appreciate the enormity of the difficulties facing any scientific explanation (let alone one which relies on replication errors) for the unimaginably complex self-replicators that we see everywhere in the living world. 

The full article is open-access and can be found here.