Evolution Q&A: How does DNA decide?

I often run into folks who have questions or misunderstandings about Evolution, so I’ve decided to write a series of articles to address these recurring ideas. Hopefully, this will be helpful! Today’s commonly asked question:

How does DNA know what works and what doesn’t? Where’s the intelligence to make decisions?

An idea that pops up a lot when discussing Evolution is the idea of agency and intelligent action. The idea at the root of question is that someone or something is either having to choose between what is good or what is bad, or having to choose to take an action to mutate into something else. This is born from a misunderstanding of how evolution works, but it is an understandable confusion. It’s natural for humans to look for something to make the decisions when stuff happens.

This misunderstanding is often due to people envisioning evolution as a process that is happening on one particular individual. I blame that stupid ape-to-human image that is used everywhere. Bad Monkey to Man Evolution ImageIf you envision evolution has happening to one individual animal, then it can make a certain kind of sense that the mutations that happen to the DNA better be absolutely correct on the first try, otherwise it’s all over and you’re dead. End of story.

The real story is that Evolution happens to an entire population of animals simultaneously (let’s choose wolves for this discussion). The DNA doesn’t decide to make a Change A because it thinks Change A will be beneficial, what happens is that you have 100,000 wolves and every new cub has slightly different DNA from the parents due to basic genetic reproduction as well as errors during copying (i.e. mutations). So, imagine this new generation of 100,000 wolf cubs is actually 100,000 DNA experiments. All of the Wolf DNAs are slightly different. That’s step 1. Due to simple reproduction and accidental mutation, you now have 100,000 accidental experiments.

Step 2 is where the the true, non-random, power of Evolution comes into play…

Natural selection is where the action happens that looks like decisions are being made. However, there isn’t anyone or anything actively looking at all of the options and picking out which one is good and which one is bad. There is no DNA intelligence (or supernatural intelligence) sifting through all of the 100,000 experiments to pick out the ones it likes. Out of those 100,000 DNA experiments, some of them will be detrimental to the health of the wolf and those cubs will die young or even never be born. Some of those DNA experiments/mutations won’t have much of a tangible effect at all. However, maybe ~1,000 (i.e. 1%) of those mutations might make those cubs slightly faster, or perhaps a give those cubs slightly warmer coats of fur. The cubs who are faster will be able to catch food more easily and evade other predators more easily. Or perhaps we get a particularly cold winter and those cubs with thicker fur are able to survive the winter while other cubs are more likely to die.

What is effectively happening is that all possible “choices”/experiments are being tried simultaneously. The wolves that happened to get bad combinations die off more often before having cubs and the mutations that happened to be good ones are able to survive and produce more cubs. So, it’s not about a particular wolf, it’s about the entire population. 1% of the population had positive mutations to start. Let’s say the 1% of the wolf population are able to survive long enough produce more cubs on average than other wolves, so now those DNA mutations make up 1.5% of the population. Then take into account that the wolves without those positive mutations are more likely to die off which means the total number of wolves in the population is lower so those wolves that were 1.5% of the population are now 2% of the popluation.

That 2% of the wolf population continues to make more cubs, which continue to do a better job surviving than the other 98% of the wolf population. So after another couple generations, the wolves with those positive mutations make up about 6% of the population. Several more generations, and they make up 10% of the population.. then 17%.. then 23%, and on and on. The “rich” are getting “richer”, so to speak. No intelligence is having to make any decisions. Random changes are providing real benefits which mean they slowly become the most common type in the population.

Still not sure what I mean? Take a look at this homemade coin sorting machine:

You can dump all of the coins onto the top randomly and as they move down across the machine they naturally fall into the spots that fit well for them. That’s the natural selection part. The coins aren’t deciding which section to go into. The machine isn’t looking at each of the coins and choosing to let this one fall here and let that one fall there. They are just landing in the spot that naturally fit for them. That’s how something can seem to be driven by an intelligent choice, but actually be done mindlessly by simple natural processes.

I hope this helps explain, but if anything isn’t clear or if you have other questions you’d like me to address, please comment below!