tl;dr this is not a post about wasps, it’s about junk DNA, and that asking ‘what is a thing for?’ is often an unhelpful question

What is a wasp for? What is the purpose of a wasp? I hope that scientists (and others) find the answer straightforward – a wasp isn’t for anything. It is an organism that has evolved, there is no higher-purpose, and it sounds quite creationist to phrase questions in this way.

What is this DNA for? What is the purpose of a DNA sequence? DNA sequence is for carrying information from one generation to the next. DNA’s purpose is to contain the information to build and adapt the organism. Or is it?

Why is this second example about DNA different from the first? Why is it OK to talk about it in this way, when we shouldn’t talk about wasps this way? It isn’t OK. The DNA sequence, like the wasp, has also evolved by the evolutionary forces of mutation, recombination, gene flow, drift and selection without a higher purpose.

The dark corners where purpose hides

The slightly strange question above about wasps are asked many times, Google it, and similar phrases are repeated by the media even though those who ask aren’t particularly religious. They just think that purpose is an appropriate topic. As scientists we stay well away from this, but there are a few dark corners where purpose still hides. One such place is what the DNA in your genome is for, especially when considering junk DNA.

Of course individual level selection allows us to quite reasonably ask how components (DNA) function to promote the individual organism. But evolution acts in more complex ways. Studies (and theory) show mutation and drift are very powerful forces shaping the contents of your genome and we definitely would not expect every sequence to have a function maintained by selection.

So why, especially when talking about junk DNA, or extreme genome size, is it OK to ask “what is it for?”

The question itself is a failure

Sure, you can ask if a region of DNA sequence has a function, but shouldn’t ask what it is for. Not unless everyone hearing you understands that this is shorthand for selected-effect function (Doolitle & Brunet 2017). But it is clear that this is almost never the case for written work, people read “what is it for?” and start to frame the question in unhelpful ways that sound like old-fashioned group selection, or creationism. This language leads people astray.

Recently there has been discovered a new record holder for largest genome size, a fern (Fernandez et al 2024). Of course a journalist can ask “what is all the DNA for?” and a scientist responds, but normally not very well. What strategy do I suggest? Maybe something like this:

Journalist: “What is all this DNA for?”

Scientist: “That is an interesting question. Of course in modern science we don’t state things like that anymore, like there is a higher purpose. But if you mean, ‘what is it’s function?’ it might not have one, and that’s OK. The vast majority of organismal DNA is repetitive DNA or transposons, and evolves by mutation and drift. They accumulate over time, and each eventually just decays into broken copies, the ‘ghosts’ of old transposons. This is really well characterised in lots of species, and although it seems weird on first hearing, our detailed observations match really well to the genetic theory of what we should expect.”

Journalist: “So its junk DNA?”

Scientist: “Yes! Junk DNA is a very cool topic. Perhaps 50% of the human genome is like this, decaying copies of old transposons, sequence repeats, and virus DNA. Its interesting to consider the evolution of all this DNA sequence, transposons making copies of themselves, viruses integrating into your genome (yes about 1% of your DNA is virus). Some plants have much more junk with >80% of their genome these sorts of sequences. The functional regions, protein-coding genes and non-coding regulatory and functional sequences, are a small percentage, but they still do all the really cool stuff”

Ecosystems

Many articles say “wasps are an important part of the ecosystem…” Though this is true, it doesn’t address the question of purpose. Is it true that what they are for is to be part of an ecosystem? Is that how we think about nature? Surely organisms evolve, some come and some go, they are part of a current ecosystem that we can describe, but that is not a purpose.

Transposons, repeats, and old viral sequences could also be considered part of a genomic ecosystem. This is just an analogy, but allows us to frame things in a similar way. The purpose is not to be part of a genomic ecosystem, even though they are. The ecosystem is something that results from the evolved collection of DNA that is present.

What is it for?

So what is a wasp for?

It wasn’t put here to annoy you at picnics, its an organism that has evolved, by all the usual means, and has no higher-purpose. Its not here to be part of an ecosystem (although it is), its not here to control other insects or eat rotting fruit (although it does). It evolved and will continue to do so, making new wasps each year. Wasps are very cool when you get to study them.

What is all this intergenic transposon DNA for?

It wasn’t put here to annoy you during genome annotation, it’s sequence that has evolved, by all the usual means, there is really strong evidence that it has no function, and certainly has no higher purpose. It’s not here to be part of a genomic ecosystem, it’s not here to create mutations and variability (although it does). It evolved and will continue to do so, making new copies of repetitive DNA and transposons each generation. Junk DNA is very cool when you get to study it.

Refs

Chen J, Wang Z, Tan K, Huang W, Shi J, Li T, et al. A complete telomere-to-telomere assembly of the maize genome. doi:10.1038/s41588-023-01419-6

Doolittle WF, Brunet TDP. On causal roles and selected effects: our genome is mostly junk. doi:10.1186/s12915-017-0460-9

Fernandez et al 2024. A 160 Gbp fork fern genome shatters size record for eukaryotes https://doi.org/10.1016/j.isci.2024.109889

Image credit: European wasp (Vespula germanica) By User:Fir0002, GFDL 1.2, https://commons.wikimedia.org/w/index.php?curid=1931193. The rest of the DNA-wasp image was created by me, use as you see fit, CC0.