A study by University of Washington researcher Joshua Akey dating the age of more than 1 million single-letter variations in the human DNA code reveals most of these mutations are of recent origin, with more than 86 percent of the harmful protein-coding mutations of this type appearing in humans just during the past 5,000 to 10,000 years.
Humans have been around for roughly 100,000 years.
While each specific mutation is rare, the findings suggest the human population acquired an abundance of these single-nucleotide genetic variants in a relatively short time, Akey said.
"The spectrum of human diversity that exists today is vastly different than what it was only 200 to 400 generations ago," the genome scientist said in a university release.
Larger populations, as they multiply by producing children, have more opportunities for new mutations to appear, he said, and the number of mutations increases with accelerated population growth, such as the population explosion that began around 5,115 years ago.
Although the enlarged mutational capacity resulting from population growth has led to a greater incidence of genetic disorders among the world's 7 billion people, there is brighter side to the story, Akey's research group said.
Mutations have fostered the great variety of traits seen among modern humans, researchers said.
"They also may have created a new repository of advantageous genetic variants that adaptive evolution may act upon in future generations," they wrote in the study published in the journal Nature.