What’s wrong with this sentence: “This is how evolution stops bad mutations building up to dangerously high levels in a species”? I count at least four things wrong…
This musing was prompted by the following snippet:
When we reproduce, our children inherit a shuffled bag of mutations, and those with a collection of particularly bad ones are more likely to die before having children of their own. This is how evolution stops bad mutations building up to dangerously high levels in a species.
It comes from an otherwise interesting article on “junk” DNA in New Scientist, which in turn is a summary of a paper in Genome Biology and Evolution, DOI: 10.1093/gbe/evx121, however my musing is not on junk DNA but junk science writing, which is a topic that interests me from time to time.
I think this is bad science writing (Warning: high probability of bees in bonnets). Before I explain why, let me give a brief (and also probably bad) summary of the theory of evolution. This isn’t detailed or complete, but I hope it’s enough to demonstrate the problems with that sentence:
The theory of evolution tries to explain and predict the process of genetic survival and genetic change in species of organisms. DNA ultimately determines many of the characteristics of an organism. If, on average, those characteristics allow the organism to survive in its environment at least until it reproduces, its DNA will probably be passed on to the next generation. Equally, if the organism’s characteristics mean that it dies or is less likely to reproduce then its DNA is less likely to be passed on. Thus successful (likely to survive) DNA and successful changes to DNA (mutations) are likely to persevere and increase, and unsuccessful DNA and changes will become less frequent or disappear. Lastly, if a change in the environment means that different characteristics and changes become more likely to survive then over time that will cause a shift in the kinds of DNA and changes that survive. The theory of evolution predicts that the reason changes to DNA persist or die out is therefore whether, on average, over time, they confer a survival advantage or a disadvantage, and predicts why changes in the environment often result in changes to organisms.
So what is wrong with the sentence: “This is how evolution stops bad mutations building up to dangerously high levels in a species”? In summary:
- Evolution is not a thing, a being, or an entity – it’s a theory about a statistical and chemical process;
- So evolution does not “stop” (or for that matter, “allow”) anything, including mutations; mutations are in fact a part of the theory, but evolution doesn’t cause them, either.
- A mutation in DNA is simply a change. Potentially every part of DNA was initially caused by a mutation, but after one generation it’s not a mutation, it’s just DNA so to talk of mutations “building up” is confusing.
- Describing a change as “good” or “bad” is meaningless unless you specify whether you’re talking about survival of the species or survival of the change, which isn’t done here. In any case to talk of evolution as “stopping bad mutations” conjures up the image of a being (evolution) examining a change and making some value judgement about it, which is totally misleading.
- The speed of change in the environment may lead to the extinction of a species if the speed of change in its DNA cannot keep pace with required changes to its characteristics, but this doesn’t mean the doomed species’ DNA has “bad” changes, or, rather, that a change that once was “good” is now “bad”. All that you can say about any aspect of DNA is whether, at any instant in time, on average it advantages or disadvantages (or is neutral) for individuals in the population before they reproduce.
- In a constant environment a change in DNA should “build up” (become more frequent in the population) if one of two things is true: either the change confers an advantage to individuals that possess it, or, the change confers no advantage but is genetically carried along with some other change that does. In fact, in some cases a change that is disadvantageous may be carried along with another that is advantageous. That is, a change building up does not necessarily mean that it is “good”, and a change dying out may equally not say anything about its “badness”.
- The frequency of occurrence of a gene in a population can be described as high or low. To describe that frequency as “dangerously high” is misleading and in the context of the theory, meaningless. If it did get “dangerously high” would that mean evolution had failed? A theory can fail to describe a process, but the theory of evolution can and does explain ways in which a population can contain high frequencies of disadvantageous (“bad”) DNA, and evolution (the process) does not necessarily “stop” this from happening.
So, as I understand the theory of evolution, it predicts that disadvantageous DNA and disadvantageous changes to DNA will, over time, reduce in frequency in a population. Or, to paraphrase the article, evolution predicts “bad mutations won’t build up to high levels in a species”.
In summary, then, the sentence says “Evolution stops bad things from becoming dangerous because that’s what evolution does”!
Apart from being circular, this also reifies a theory and turns its effects into the outcomes of deliberate actions by some homunculus, an anthropomorphised actor making deliberate choices about “good” and “bad” and “dangerous”, rather than the completely dispassionate outcomes of a statistical process overlaid on the survivability of an organism (expressed by its DNA) in its current environment.
Now you might think this is all a storm in a teacup. Obviously, I disagree.
You could argue that all of these faults arise simply from trying to simplify or summarise the process that the theory describes, and giving it the shorthand label “evolution”, instead of something ponderous like “the processes predicted by the theory of evolution”, but I believe that this isn’t just an honest mistake. Rather, it’s an example of sloppy thinking that turns the shorthand name of a theory – an explanation of statistics, genetic change and survival – into an actual thing in its own right that makes decisions and stops bad things from happening.
It turns the whole idea upside down, from a description (and prediction) about how completely mechanistic forces and statistical processes can produce genetic change, into an independent force “evolution” that makes decisions and has goals or values: “This is how evolution stops bad mutations…”. No! Evolution doesn’t “stop” anything. Observation tells us that organisms with DNA that creates badly adapted characteristics are less likely to survive and reproduce. The theory of evolution predicts that, over time, this will lead to a reduction or removal of that DNA from the population. This isn’t because it “wants” to, or because the changes are “bad”. Evolution doesn’t “do” anything! Organisms with certain characteristics die because they aren’t adapted to the environment. The environment kills them, not evolution, and not DNA. This has an effect on the DNA available for breeding and hence preservation in the pool of available DNA. We call this whole process evolution, but its outcomes are the results of chemistry and statistics, not the theory.
From describing evolution as an actor it’s only a small step to pitting this actor “evolution” against some other actor that some people claim is responsible for the same outcomes: “god”. It completely changes the notion of a theory with observations and predictions into a sentient actor that makes choices and has values; it totally removes the fundamental scientific basis for the theory and its operation, and makes it equivalent to any other arbitrary actor.
In short, I don’t think it’s a defensible abbreviation for a longer, more correct sentence. I think it’s a dangerously inaccurate characterisation that obscures science and encourages reification.
The most annoying thing about the sentence is that the preceding sentence is a perfectly good summary of evolution. What should have followed (if anything) was: “The theory of evolution predicts how the processes of survivability and statistics will, over time, reduce the frequency of DNA containing low-survivability changes due to mutations, resulting in a higher proportion of survivable DNA, because well adapted organisms will survive and pass on their DNA and maladapted ones will not.”
Now your tea is cold.