At least 75 per cent of our DNA really is useless junk after all

Luckily, our children don’t inherit too many dangerous mutations

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You’re far from a perfect product. The code that makes us is at least 75 per cent rubbish, according to a study that suggests most of our DNA really is junk after all.

After 20 years of biologists arguing that most of the human genome must have some kind of function, the study calculated that in fact the vast majority of our DNA has to be useless. It came to this conclusion by calculating that, because of the way evolution works, we’d each have to have a million children, and almost all of them would need to die, if most of our DNA had a purpose.

But we each have just a few children on average, and our genetic health is mostly fine. The study therefore concludes that most of our DNA really must be junk – a suggestion that contradicts controversial claims to the contrary from a group of prominent genomics researchers in 2012.

Junk or not?

When researchers first worked out how DNA encodes the instructions for making proteins in the 1950s, they assumed that almost all DNA codes for proteins. However, by the 1970s, it was becoming clear that only a tiny proportion of a genome encodes functional proteins – about 1 per cent in the case of us humans.

Biologists realised that some of the non-coding DNA might still have an important role, such as regulating the activity of the protein-coding genes. But around 90 per cent of our genome is still junk DNA, they suggested – a term that first appeared in print in a 1972 article in New Scientist.

But throughout the 2000s, a number of studies purported to show that junk DNA was nothing of the sort, based on demonstrating that some tiny bits of non-coding DNA had some use or other. These claims proved popular with creationists, who were struggling to explain why an intelligently designed genome would consist mostly of rubbish.

The grandest claim came in 2012, when a consortium of…

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