Humans, Neanderthals not related, UA scientist finds

Wildcat File Photo Arizona Daily Wildcat Research assistant Anne Stone explains DNA coding and the process of polymerase chain reaction that she used in her lab to examine Neanderthal DNA. Stone has concluded that humans are not genetic descendants of the prehistoric creatures.

University of Arizona research assistant Anne Stone and her colleagues have examined DNA samples extracted from Neanderthals and concluded that humans possess similarities to, but no clear kinship with, the furry beasts of the past.

"It was very exciting," Stone said. "We always knew Neanderthals were closely related to humans, but do we descend from them or are they our cousins?"

Stone and her research team concluded that although humans and Neanderthals are "cousins," evidence does not support earlier theories that humans descended from the ape-like creatures.

Neanderthals' place in the human family tree has been uncertain for more than 150 years, ever since the first remains were discovered in Germany's Neander Valley in 1856. Tal means "valley" in German, hence the hominids' name.

Scientists believed Neanderthals were a primitive form of humans despite their low, broad cranium, sloping forehead and large nasal openings - all of which differ from modern humans.

Neanderthals inhabited Europe and the Middle East until about 30,000 to 100,000 years ago. It is difficult to pinpoint a date because the Neander Valley, where the first bones were uncovered, has since been destroyed by quarrying and further research cannot be done there, Stone said.

"Unfortunately, we can't go back and get a better date," she said.

Anatomically modern humans originated in Africa tens of thousands of years before the Neanderthal roamed Europe or the Middle East.

In the early 1990s, new methods of dating artifacts were developed, which established that Neanderthals and humans coexisted for several thousand years before the Neanderthals' disappearance.

The "Out of Africa" hypothesis, championed by Christopher Stringer of London's Natural History Museum, holds that early humans migrated to Europe and Asia, where they out-competed and replaced the less advanced Neanderthal.

"I doubt people were coming in waving clubs and killing Neanderthals," Stone said.

Other theories speculate that early humans introduced new devastating diseases, causing the Neanderthals to perish, or that hominids and humans interbred, suggesting that Neanderthals were a genetic ancestor. The number of human genes would have dominated the Neanderthals' genes because of population size and would have eventually led to their demise.

Stone's research has dispelled that theory by proving that human genetics differ too much from that of the Neanderthal for any ancestral relationship to exist.

The findings help establish the reason for the Neanderthals' disappearance, Stone said.

"It suggests that people from elsewhere, probably Africa or the Middle East, moved to Europe and out-competed the Neanderthals," she said.

By using DNA extractions from the right humerus bones in Neander Valley, Stone and her colleagues at Pennsylvania State University and the University of Munich were able to find the Neanderthal's genetic sequence. A genetic sequence is a DNA code unique to each individual.

Svante PŠŠbo, a zoology professor at the University of Munich, and researcher Mathias Krings were able to test the DNA strands before sending samples to Stone and Mark Stoneking, associate professor of anthropology at Penn State.

The Neanderthals' DNA required gentle handling because it is so old.

"Typically, ancient DNA has been degraded into small pieces," Stone said.

Because ancient DNA is difficult to handle, special labs are used to prevent modern DNA from contaminating samples. A mere skin cell can ruin a sample, making the process complicated for scientists.

"If any modern DNA falls into your tube, it will be preferentially amplified," she said.

To duplicate DNA a method called polymerase chain reaction is used.

"It's equivalent to the modern Xerox machine," she said.

DNA exists in a double helix, two strands coiled around each other, which must be separated. That is done by heating the sample to 94 degrees Celsius.

Human primers, small pieces of DNA that match the beginning of the sequence to be amplified, are bonded to the separated strands, forming a new double helix out of a single strand, called an extension.

"It's kind of like the old shampoo commercial where you tell two people, and they tell two more people, and it keeps doubling," Stone said.

The Munich team started the process in 1996 before sending the strands to Stone to repeat it and confirm their findings.

"We got the same sequence," she said, adding that it took her about two months to do it.

But she plans to continue her research because "two is a pretty small sample," she said. Stone plans to transfer to the University of New Mexico in January to set up an ancient DNA lab.

She intends to research the DNA further by testing more Neanderthal and early human samples to compare the differences of the two coexisting creatures.

Stephanie Corns can be reached via e-mail at Stephanie.Corns@wildcat.arizona.edu.