"Otzi," the oldest known intact, naturally preserved human body, was found in a glacier in the Otztal Alps in 1991. He is thought to have died in 3,300 BC.

Otzi was murdered. Researchers using medical imaging technology discovered an arrowhead buried deep beneath Otzi's left collarbone.

All humans living outside of Africa today are descended from perhaps 150 "behaviorally modern humans" who crossed from Ethiopia to Arabia about 50,000 years ago, wrote New York Times science writer Nicholas Wade in his fascinating book, "Before the Dawn."

Mr. Wade's book is based on recent discoveries in genetics (the full sequence of DNA units in the genome wasn't determined until 2003), which shed new light on man's pre-history. (History began about 5,000 years ago — around the time of Otzi's death — when writing first appeared.) Homo sapiens weren't the only human species then. Neanderthals ranged across Europe down to what's now Israel. Homo erectus had reached Asia about one million years ago.

We killed them off, Mr. Wade said. Since the Neanderthals were physically more robust than we are, and had brains as large or larger, this was no mean feat. Our secret weapon, Mr. Wade speculates, was language. Because we could communicate with each other, we could cooperate in ways our rival human species could not. "Before the Dawn" is well researched and very well written. I recommend it to all the intellectually curious, but that's not why I'm writing this column. Mr. Wade details two gross distortions of scientific evidence for political purposes.

Some 65 percent of primitive societies were at war continuously, estimates Lawrence Keeley, an archeologist at the University of Illinois-Chicago. A typical tribal society lost about one half of one percent of its population in combat each year, he said.

"To understand much of today's war, we must see it as a common and almost universal behavior," said Harvard archeologist Steven LeBlanc.

Despite the evidence, since World War II many archeologists and anthropologists have been promoting the myth of the peaceful savage. Otzi was initially described as a shepherd, though found with his body were a bow, a dagger and an axe. Prof. Keeley told Mr. Wade that a grant application he'd made to study a Neolithic ditch and palisade was rejected until he changed his description of the structure from "fortification" to "enclosure."

The second major distortion has to do with race. Geneticists have identified five races — Africans, Caucasians, Asians, Pacific Islanders and Native Americans — based on the continents on which each race developed, Mr. Wade said. (Interestingly, skin color is not, he said, a good indicator of race. For instance, both fair-skinned Scandinavians and dark-skinned Indians are Caucasians.) Yet recently the deputy editor of the New England Journal of Medicine wrote that "race is a social construct, not a scientific classification."

It is one thing for sociologists to prattle on so, but it is disturbing to have someone with scientific training rejecting scientific fact because it is deemed politically incorrect. It's also dangerous, Mr. Wade said, because different racial groups have different susceptibilities to disease.

Which brings me to the furor created when NASA administrator Michael Griffin told National Public Radio he doubted global warming was really a problem. When the politically correct exploded, Mr. Griffin apologized for airing his views, but not for their contents.

Nor should he. It is a matter of faith among the politically correct that the evidence for man-made global warming is so strong there is no longer room for debate. The "evidence" they cite most frequently are the claims of the U.N.'s Intergovernmental Panel on Climate Change.

But when Lawrence Solomon interviewed two dozen top scientists for a series of articles in Canada's National Post, he learned that "many say their peers generally consider (the IPCC) to have little or no credibility. In one case, a top scientist told me that, to his knowledge, no respected scientist in his field accepts the IPCC position."

When Mr. Solomon asked the UN for a list of the scientists allegedly supporting the IPCC position, he was turned down.

The theory is that carbon dioxide emissions from our factories and automobiles are warming the planet. But the evidence from earlier warmings is that carbon dioxide concentrations in the atmosphere increased after, not before, the warming trend began.

Scientists do science a disservice when they massage evidence to fit politically correct conclusions, or ignore it altogether.