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Evolution Has No Plan: Why Organisms Don’t Rewrite Their DNA
**A quick explanation of some common misunderstandings about evolution.**
Scientists should engage with the general public. Translating complex, nuanced research into clear and digestible language matters, especially in the current age of misinformation. However, this task is anything but easy. Much of the public appears to have the attention span of a goldfish with amnesia, happily cherry-picking fragments of information that confirm pre-existing beliefs. Journalists, meanwhile, are often more interested in eye-catching headlines rather than in high-quality research. To make matters worse, they frequently report on topics well outside their expertise, leading to the spread of common misunderstandings and a lack of nuance.
These problems were on full display in the recent coverage by several news outlets, such as _The Guardian_ and _BBC_ , which uncritically reported that polar bears are “rewriting their DNA in response to climate change.” Not one of these articles evaluated the claims of the original study, nor did any of the journalists bother to consult independent experts for a second opinion. The latter approach is especially advisable when writing outside your expertise, such as the Belgian journalist at _VRTNWS _who has a background in history (but clearly not in evolutionary biology). Instead, most journalists simply regurgitated the press release.
The original study itself has several serious issues, which I discussed in detail on my _Avian Hybrids_ blog. Here, however, I want to focus on something more fundamental: the deeply misleading picture of evolution that was presented to the public. In _The Guardian_ , for example, the lead author is quoted as saying that “polar bears in the warmest part of Greenland are using ‘jumping genes’ to rapidly rewrite their own DNA.” This phrasing strongly suggests that the bears are actively modifying their genomes in response to rising temperatures. That is not how evolution works.
**Darwin’s Finches**
Let’s start with the basics of evolution by natural selection, the groundbreaking idea of Charles Darwin. The logic is deceptively simple and rests on just three observations.
1. Individuals show **variation** in certain traits.
2. These traits are **heritable** (i.e. offspring look like their parents)
3. Variation in these traits impacts **survival and reproduction rates**
This process has been demonstrated beautifully by the long-term work of Peter and Rosemary Grant on Darwin’s finches. In the Medium Ground Finch (_Geospiza fortis_), they quantified both variation and heritability in beak size. The graph below illustrates this clearly: individual variation is obvious from the spread of points, while heritability is evident from the strong correlation between parental bill depth (horizontal axis) and offspring bill depth (vertical axis).
By following these finches over multiple years, the Grants also showed that survival and reproduction are not random. It depends on beak morphology. During dry years, birds with larger, more robust beaks have a survival advantage (e.g., the 1977 La Nina-event). During wet years, smaller-beaked individuals fare better (e.g., the 1983 El Niño-event). These shifting survival patterns translate directly into measurable changes in beak size over time. Evolution by natural selection.
_Darwin’s Finches illustrate evolution by natural selection. The left graph depicts variation as well as heritability in beak size. The right graph shows how dry (1977) and wet (1983) conditions impact survival rates, and consequently drive changes in beak morphology. Based onGrant & Grant (2002)._
**No Foresight**
The key takeaway from the Darwin’s Finches example is simple: these birds have no foresight. They do not decide to grow larger or smaller beaks, nor do they “rewrite” their genes in anticipation of environmental change. Instead, they just display heritable variation in beak size, and the environment merely selects from that variation, favoring one beak morphology over another. As a result, populations become better adapted to local conditions. Crucially, when the local conditions change, the rules will change as well. Traits that were once advantageous may become liabilities, and different variants well then be favored. Over time, this process produces evolutionary change. No planning required.
Hence, the claim that “polar bears in the warmest part of Greenland are using ‘jumping genes’ to rapidly rewrite their own DNA” is not just sloppy. It is flat-out wrong. Instead, these bears show variation in gene expression (potentially driven by “jumping genes”) from which natural selection could select the individuals that are best adapted to the local conditions (which might involve increasing temperatures). No foresight. Just heritable variation and natural selection.
**Random Mutations**
The absence of evolutionary foresight brings me to another persistent misunderstanding: the randomness of mutations. This idea is often misconstrued into the claim that “every mutation is equally likely to occur.” That is simply false. We know perfectly well that some regions of the genome mutate more frequently than others (so-called mutation hotspots). A very nice example concerns a fragile section in the genome of stickleback fish (_Gasterosteus aculeatus_) where enhanced mutation rates facilitate repeated adaptations to new environments.
What random actually means in an evolutionary context is quite different: mutations occur without reference to environmental needs. They are not tailored responses to local conditions. Genes for larger beaks do not mutate because large beaks are advantageous. A mutation does not occur because an organism “needs” it. Evolution does not work like a wish list. Individuals do not summon helpful mutations on demand.
These insights explain why the claim that polar bears can “rewrite their DNA in response to climate change” is nonsense. Mutations happen regardless of climate change, not because of it. At most, changing conditions (such as higher temperatures) might influence overall mutation rates. But even then, the mutations themselves remain blind to what would be useful.
**An Entangled Mess**
Taken together, these points expose just how deeply misleading the “DNA-rewriting polar bears” narrative really is. Evolution is not a rapid-response system that detects environmental change and engineers genetic solutions on demand. It is a blind, undirected process driven by heritable variation, random mutations, and natural selection.
Also keep in mind that this blog post has still been a simplification. Evolution is messier and more complex than the stripped-down version presented here, involving additional layers of complexity such as genetic drift, gene flow, developmental constraints, and historical contingency. Nature rarely follows neat narratives or headline-friendly metaphors, and evolution certainly does not oblige to our desire for simple stories. Precisely because it is subtle, unintuitive, and endlessly intricate, evolution remains such a fascinating process to study. And as scientists, we should do our best to convey the nuances of this beautiful theory to the general public. Charles Darwin put it best.
> There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.
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