100M-Year-Old DNA Regions Baffle Experts

Certain regions of mammalian DNA with no discernible purpose have one perplexing characteristic in common: They have survived, without mutation, for as long as 100 million years, LiveScience reports. Scientists speculate that the areas have some deep purpose, but for now they know only that they are “ultraconserved regions,” some 300 times less likely to mutate than other parts of the genome.

Scientists engineered mice DNA to lack certain of the regions, with no evident decrease in health or genetic change. Further investigation showed an almost perfect correlation in the regions on the genes of mice, dogs, and humans, suggesting they were being actively conserved for some reason. “Imagine that these regions somehow protect you from a disease that only strikes the population every once in a while,” hazarded one scientist. (More genome stories.)