LAST WEEK, researchers announced that a small plant found on the Pacific island of New Caledonia has the largest genome ever known to science.
 
DNA comes in base pairs: each of the four possible bases (denoted by the letters A, T, C, G) is matched by a counterpart on the other strand of DNA in the double helix. Our human genome has around 3 billion base pairs. This little fern with the scientific name Tmesipteris oblanceolata has over 160bn.
 
As yet, scientists don’t have the sequence of the entire genome. But they don’t need to know that to prove that its size is record-breaking. To measure the genome size they dyed the cell nuclei — where the fern’s genome is stored — and compared how much dye there was to the previous record holder, a sub-alpine Japanese plant called Paris japonica with delicate white flowers. Two different methods gave a very similar result, showing that the fern had a substantially bigger genome.
 
Both animals and plants are within a larger grouping of life called eukaryotes. The previous record holder for a eukaryote genome before Paris japonica was a fish called the marbled lungfish. The fish can grow up to 2 metres long, but its genome is the real whopper, weighing in at 133bn base pairs. Both have now been bested by the fern.
 
It’s unclear why organisms show such a massive variation in genome size. It remains a scientific enigma — some scientists go as far as calling it a paradox. Naively, scientists once believed that the bigger the genome the more complex the organism. But accepting that humans are less complicated than a fern or a lungfish isn’t simply a bitter pill to swallow — it seems very wrong.
 
Part of the answer is that most of the DNA in eukaryote genomes does not encode genes. In the human genome, only about 1 per cent of our genome is in genes which encode proteins. So what does the other 99 per cent of the genome do?

It was once dismissed by some scientists as “junk,” but it’s now well-established that it can also play important roles in regulating how genes are turned on or off.
 
It seems very unlikely that the huge non-coding DNA parts of these mega genomes could all be essential to the organism. Bits of DNA that serve only to replicate themselves can proliferate in the genome, copying themselves many times over like a computer virus or a cancer.

As long as they don’t undermine the organism’s ability to survive, the total genome size can just keep growing. Even though non-coding DNA can have useful functions, that doesn’t mean it always does: a large part of these massive genomes is repeated DNA, the same sequence multiplied again and again, creating a bulk of “junk.”
 
There are likely good reasons why most organisms don’t have these kind of huge genomes. One of the study’s co-authors, Ilia Leitch, told Nature that the large size of the genome probably dilutes the useful parts — its genes — even more, raising the question of how the cell even manages to access them: “It’s like trying to find a few books with the instructions for how to survive in a library of millions of books — it’s just ridiculous.”
 
Analogies from our world into the world of the cell can be misleading. But it’s true that every time the organism copies a cell it needs to replicate the genome in full. Lugging around and copying all that pointless extra material has some negative effects.

Plants with big genomes are slow-growing because of the energy and time that copying the genome takes and need more nutrients to produce all that extra DNA. But in the cases of these species with giant genomes, the cost is clearly not enough to drive them extinct.
 
More familiar organisms also have big genomes. The common onion, Allium cepa, has a genome about five times the size of the human genome. The biologist T Ryan Gregory proposed that when people are proposing exciting explanations for the real function of “junk” DNA in humans, they should apply the onion test: “Can I explain why an onion needs about five times more non-coding DNA for this function than a human?”

As Gregory pointed out, even for species within the genus Allium the genome size can vary massively: wild garlic has a genome four times bigger than chive, for no apparent reason.
 
In contrast, John Mattick has argued that while some eukaryotic genomes clearly have unnecessary baggage, “the extent of such baggage in humans is unknown.”
 
This argument blew up several years ago when one group of scientists working for a project called Encode claimed to have found that 80 per cent of the non-coding part of the human genome was “functional” — for a quite specific definition of function. Some interpreted the results to mean that humans had very little baggage in our genomes.

However, critics of Encode argued that it was an “absurd conclusion” deriving from “many logical and methodological transgressions.” Responding to one scientist involved with Encode who had commented that textbooks would need to be rewritten, one group of critics said cattily, “We agree, many textbooks dealing with marketing, mass-media hype, and public relations may well have to be rewritten.”
 
The huge genome of this tiny fern reminds us that plants and other organisms with giant genomes clearly have a lot of baggage, the remnants of millions of years of random trial and error. So does the human genome — it isn’t all “junk,” but a large portion probably is.

However, without space to manoeuvre, there is no possibility of change. That it all somehow works despite the amount of baggage is testament both to the power of evolution and the probable unimportance of a lot of this variation.
 
The tiny fern received a lot of attention in the news. But the scientific news comes against a backdrop of protests in New Caledonia which have been far less reported in the British media.

The island is an overseas French territory which was colonised by French settlers in 1853, with the suppression of the indigenous population. The population is made up of 41.2 per cent indigenous Kanak people, although numbers of French emigrants continue to move to the islands.

Proposed electoral reforms will see the relative electoral power of non-indigenous inhabitants increase, and Kanak activists believe threaten the future possibility of independence.
 
In 2018 an independence referendum saw 43.6 per cent voting for independence. There have been two since. Five Kanak protesters and two police officers have died in the last three weeks and 3,000 French military or “security personnel” are mobilised in New Caledonia to enforce a 12-day state of emergency and curfew, and to suppress protests.
 
Though the knowledge about the tiny fern’s genome doesn’t depend on knowing this, it’s indisputable that colonialism and science in New Caledonia are linked, both historically and today. This research was done by a majority European research team. It’s a reminder that science doesn’t happen in a vacuum — but none of this was mentioned in other news coverage of the tiny fern.