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What Can Chain Letters Teach us about Natural Selection?

“It is important to understand that none of these replicating entities is consciously interested in getting itself duplicated. But it will just happen that the world becomes filled with replicators that are more efficient.”


In 1859, Charles Darwin first described his theory of evolution through natural selection in The Origin of Species. Here we are, 157 years later, and although it has become an established fact in the field of biology, its beauty is still not that well understood among the populace. I think that's because it's slightly counter-intuitive. Unlike string theory or quantum mechanics, the theory of evolution through natural selection is pretty easily obtainable by most.

So, is there a way we can help ourselves understand the theory in an intuitive way, so we can better go on applying it to other domains? I think so, and it comes from an interesting little volume released in 1995 by the biologist Richard Dawkins called River Out of Eden. But first, let's briefly head back to the Origin of Species, so we're clear on what we're trying to understand.


In the fourth chapter of the book, entitled “Natural Selection,” Darwin describes a somewhat cold and mechanistic process for the development of species: If species had heritable traits and variation within their population, they would survive in different numbers, and those most adapted to survival would thrive and pass on those traits to successive generations. Eventually, new species would arise, slowly, as enough variation and differential reproduction acted on the population to create a de facto branch in the family tree.

Here's the original description.

Let it be borne in mind how infinitely complex and close-fitting are the mutual relations of all organic beings to each other and to their physical conditions of life. Can it, then, be thought improbable, seeing that variations useful to man have undoubtedly occurred, that other variations useful in some way to each being in the great and complex battle of life, should sometimes occur in the course of thousands of generations? If such do occur, can we doubt (remembering that many more individuals are born than can possibly survive) that individuals having any advantage, however slight, over others, would have the best chance of surviving and of procreating their kind? On the other hand, we may feel sure that any variation in the least degree injurious would be rigidly destroyed. This preservation of favourable variations and the rejection of injurious variations, I call Natural Selection.


In such case, every slight modification, which in the course of ages chanced to arise, and which in any way favored the individuals of any species, by better adapting them to their altered conditions, would tend to be preserved; and natural selection would thus have free scope for the work of improvement.


It may be said that natural selection is daily and hourly scrutinizing, throughout the world, every variation, even the slightest; rejection that which is bad, preserving and adding up all that is good; silently and insensibly working, whenever and wherever opportunity offers, at the improvement of each organic being in relation to its organic and inorganic conditions of life. 

The beauty of the theory is in its simplicity. The mechanism of evolution is, at root, a simple one. An unguided one. Better descendants outperform lesser ones in a competitive world and are more successful at replicating. Traits that improve the survival of their holder in its current environment tend to be preserved and amplified over time. This is hard to see in real time, although some examples are helpful in understanding the concept, e.g. antibiotic resistance.

Darwin's idea didn't take as quickly as we might like to think. In The Reluctant Mr. Darwin, David Quammen talks about the period after the release of the groundbreaking work, in which the world had trouble coming to grips with Darwin's theory. It was not the case, as it might seem today, that the world simply threw up its hands and accepted Darwin as a genius. This is a lesson in and of itself. It was quite the contrary:

By the 1890s, natural selection as Darwin had defined it–that is, differential reproductive success resulting from small, undirected variations and serving as the chief mechanism of adaption and divergence–was considered by many evolutionary biologists to have been a wrong guess.

It wasn't until Gregor Mendel's peas showed how heritability worked that Darwin's ideas were truly vindicated against his rivals'. So if we have trouble coming to terms with evolution by natural selection in the modern age, we're not alone: So did Darwin's peers.


What's this all got to do with chain letters? Well, in Dawkins' River Out of Eden, he provides an analogy for the process of evolution through natural selection that is quite intuitive, and helpful in understanding the simple power of the idea. How would a certain type of chain letter come to dominate the population of all chain letters? It would work the same way.

A simple example is the so-called chain letter. You receive in the mail a postcard on which is written: “Make six copies of this card and send them to six friends within a week. If you do not do this, a spell will be cast upon you and you will die in horrible agony within a month.” If you are sensible you will throw it away. But a good percentage of people are not sensible; they are vaguely intrigued, or intimidated by the threat, and send six copies of it to other people. Of these six, perhaps two will be persuaded to send it on to six other people. If, on average, 1/3 of the people who receive the card obey the instructions written on it, the number of cards in circulation will double every week. In theory, this means that the number of cards in circulation after one year will be 2 to the power of 52, or about four thousand trillion. Enough post cards to smother every man, woman, and child in the world.

Exponential growth, if not checked by the lack of resources, always leads to startlingly large-scale results in a surprisingly short time. In practice, resources are limited and other factors, too, serve to limit exponential growth. In our hypothetical example, individuals will probably start to balk when the same chain letter comes around to them for the second time. In the competition for resources, variants of the same replicator may arise that happen to be more efficient at getting themselves duplicated. These more efficient replicators will tend to displace their less efficient rivals. It is important to understand that none of these replicating entities is consciously interested in getting itself duplicated. But it will just happen that the world becomes filled with replicators that are more efficient.

In the case of the chain letter, being efficient may consist in accumulating a better collection of words on the paper. Instead of the somewhat implausible statement that “if you don't obey the words on the card you will die in horrible agony within a month,” the message might change to “Please, I beg of you, to save your soul and mine, don't take the risk: if you have the slightest doubt, obey the instructions and send the letter to six more people.”

Such “mutations” happen again and again, and the result will eventually be a heterogenous population of messages all in circulation, all descended from the same original ancestor but differing in detailed wording and in the strength and nature of the blandishments they employ. The variants that are more successful will increase in frequency at the expense of less successful rivals. Success is simply synonymous with frequency in circulation. 

The chain letter contains all of the elements of biological natural selection except one: Someone had to write the first chain letter. The first replicating biological entity, on the other hand, seems to have sprung up from an early chemical brew.

Consider this analogy an intermediate mental “step” towards the final goal. Because we know and appreciate the power of reasoning by analogy and metaphor, we can deduce that finding an appropriate analogy is one of the best ways to pound an idea into your head–assuming it is a correct idea that should be pounded in.

And because evolution through natural selection is one of the more powerful ideas a human being has ever had, it seems worth our time to pound this one in for good and start applying it elsewhere if possible. (For example, Munger has talked about how business evolves in a manner such that competitive results are frequently similar to biological outcomes.)

Read Dawkins' book in full for a deeper look at his views on replication and natural selection. It's shorter than some of his other works, but worth the time.