An evolutionary biologist at the University of Houston has published new calculations that indicate no more than 25 percent of the human genome is functional.
That is in stark contrast to suggestions by scientists with the ENCODE project that as much as 80 percent of the genome is functional.
In work published online in Genome Biology and Evolution, Dan Graur reports the functional portion of the human genome probably falls between 10 percent and 15 percent, with an upper limit of 25 percent.
The rest is so-called junk DNA, or useless but harmless DNA.
If 80 percent of the genome were functional, unrealistically high birth rates would be required to sustain the population even if the deleterious mutation rate were at the low end of estimates, Graur found.
“For 80 percent of the human genome to be functional, each couple in the world would have to beget on average 15 children and all but two would have to die or fail to reproduce,” he wrote.