Less than 10 percent of our DNA is considered to be "functional" in the sense of performing work seen as important, researchers at the University of Oxford in Britain say.
The new figure stands in stark contrast to a 2012 assessment by scientists in another DNA project that held that a full 80 percent of the human genome possesses some necessary biochemical function.
Many in genetics research argued the biochemical definition chosen for "function" that was used to create the 80 percent figure was much too broad.
Activity in DNA does not immediately suggest a consequence, they argued; functionality requires a demonstration that the activity matters, is vital to the organism, they have said.
With that in mind, the Oxford researchers set out to identify how much of the human genome has remained the same over 100 million years of evolution, a clear indication of DNA that matters, possessing some significant function that needed to be retained and kept safe from changes.
The figure they came up with was 8.2 percent.
"This is in large part a matter of different definitions of what is 'functional' DNA," says study co-author Chris Pointing of Oxford's MRC Functional Genomics Unit. "We don't think our figure is actually too different from what you would get looking at [the previous project's] bank of data using the same definition for functional DNA."
And even within the 8.2 percent, not all the genetic material is equally essential, the researchers point out.
Just slightly more than 1 percent human DNA can be linked to the proteins responsible for almost all of the human body's critical biological processes, they note.
And what is the remaining 7 percent doing?
It's probably dealing with the task of turning on and off of genes responsible for encoding those proteins, doing so in reaction to different factors, at different times and in different areas of the body, the researchers say.
The rest of our genome, outside of the "functional" 8.2 percent, is material leftover from ongoing evolution, regions of the genome that have experience gains or losses in the DNA code and are often dismissed as "junk" DNA.
"There appears to be a lot of redundancy in how our biological processes are controlled and kept in check," Pointing says. "It's like having lots of different switches in a room to turn the lights on. Perhaps you could do without some switches on one wall or another, but it's still the same electrical circuit."
The Oxford study has been published in PLOS Genetics.
