Prior posts have looked at a variety of issues related to genes and what allegedly makes humans what we supposedly are. But, is it possible that DNA that is no longer present in the genome also helped to shape us? How would we know?
Most research into homo sapien genomics has focused on teasing out those genes that are unique to humans on the assumption that these might explain what makes us "unique." But, what about DNA that is no longer present? Human appear to lack 510 "chunks" of DNA that are present in chimps, macaques, and mice. Most are also missing in Neandertals. Taking this as a significant factoid, then one can hypothecate that these DNA chunks were lost between 500,000 and 6 million years ago, in round numbers.
Only one of the missing chunks is believed to contain an actual "gene" (see http://en.wikipedia.org/wiki/Genehttp://en.wikipedia.org/wiki/Gene). The function of the rest may be uncertain, but it is possible that at least some were "switches" for turning genes off and on, a subject touched upon in prior posts. Such "enhancers" do not have to be physically located near the gene whose function they impact, though as noted in prior posts, some are. Since humans and chimps have roughly the same set of genes, some researchers have hypothesized that changing the manner in which a gene is used (e.g., by turning a gene on or off in a particular tissue or during a specific developmental phase) may yield ("evolve") new characteristics.
Because most of the missing chunks do not contain genes, it is difficult to state with any exactness what they did. Researchers applied some computational analysis to ascertain the functions that certain chunks may have performed. For example, one chunk may have enhanced the activity of the gene that controls production of facial sensory whiskers and small spines on the penises of both chimps and mice. Since humans do not have this enhancer, this gene is not turned on and the sensory whiskers and penile spines do not develop.
This is clearly the beginning of an interesting new twist on the search for what makes us what we are. What is fascinating is that impacts can be attributed to what is not there as well as what is there. Evolution thus can be thought of as embracing not only a modification of a gene or of a gene enhancer, but also of the elimination of enhancers or other control appartus. Evolution is thus not only what is, or what is changed, but also what is no longer.
The Stanford study can be found at http://www.nature.com/news/2011/110309/full/news.2011.148.html.