DNA sequences can act as "tape measures of evolution." Some highly-conserved regions of the human genome (similar to comparable regions in other species) don't code for proteins. Why? 1. Such regions coded for proteins in genomes of distant human ancestors, but over time they became noncoding; however, conserving their sequence remained unchanged.
2. Such regions play a significant role in gene regulation. That is why they remain conservative under the influence of natural selection.
3. Such regions are the sites of DNA recombination. They should remain conservative to provide an accurate recombination process during cell division.
4. Such regions remain conservative because the mutation rate differs along the genome. In other words, such regions remain conservative accidentally.