Science shows that 99.9 percent of our DNA is the same, according to the National Human Genome Research Institute, but what makes up the remaining 0.1 percent? That question has stirred much debate, and many have used the uncertainty to fuel political wars about perceived biological differences based on race. But the latest study on the subject supports previous findings that say race doesn't exist.

Here's the premise of the study: People's genes dictate their physical appearance, and how people look could be affected by natural selection (when genes adapt over time to fit specific environmental conditions). By studying this process on a global scale, scientists sought to discover how it affects population differences across the globe and to identify the types of genetic differences that usually happen as a result of natural selection to see if these factors contribute to biological differences between races.

Most changes are linked to skin pigment, hair density, diet, or immune response to certain diseases, according to findings from Lluís Quintana-Murci and colleagues at the Pasteur Institute in Paris, France, published in the February 2008 issue of Nature Genetics. The study is available for purchase here or you can read the abstract online.

Using HapMap, an international project of the National Human Genome Institute that catalogues single-nucleotide polymorphisms (SNPs) that denote tiny variations on individual genes, Quintana-Murci and colleagues were able to pinpoint the degree of differences between four populations caused by natural selection.

None of the biological differences were linked to race. Read why the White Guy says most white people think Blacks are intellectually inferior.

Of 2.8 million SNPs tracked by HapMap, the researchers discovered 55 genes that had adapted to the demands of local environments. Six involved skin pigment and hair density; four helped the immune system combat diseases that are localized in some places of the world, like malaria; six dealt with metabolic regulation. Nine other genes had different functions, none of which fuel the political melee, reports the Economist.

There are many genes for which science doesn't yet have an explanation. In this particular study, the scientists identified 30 genes involved in local natural selection whose functions are thus far unknown, reports the Economist.

Many of the genes with known functions affect multiple traits. As these genes evolve over time through natural selection, the outward impact of the process will appear greater than it is because each of these genes impacts multiple traits. For example, one gene the researchers studied--EDAR--involves hair density and sweat-gland and teeth development in humans and mice. In humans, natural selection that helps people in certain locales adapt to colder environments, for example, also impacts tooth shape.

How does this relate to race? Personal DNA testing is becoming all the rage these days, thanks in part to publicity the topic garnered when Oprah Winfrey appeared on PBS' "African-American Lives," the second part of which aired last week. What does your DNA say about you? It's tempting to think that because a DNA sample can tell us a lot about our ancestry, it can also identify us by race. To date, that's just not true.

What does this mean? Claims such as the one made by Nobel Prize winner and co-DNA discoverer James Watson that Africans are biologically less intelligent than white Europeans are without merit. There's much we don't know about genetics (no doubt Watson didn't realize his genes were 16 percent Black origin--16 times the average for white Europeans--when he made his comment), but the lack of scientific evidence doesn't stop people from trying to use genetic information to make a political point.

"All in all, the school of thought which holds that humans, for all their outward variety, are a pretty homogenous species received a boost," reports the Economist, in light of the most recent findings. But this doesn't mean the case is closed by any means. 

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