March 29, 2000
DNA Tests Cast Doubt on Link Between Neanderthals and Modern Man

By NICHOLAS WADE
Did modern humans wipe out the Neanderthal people who inhabited Europe until 
28,000 years ago, or did the two populations merge through interbreeding? New 
DNA evidence, extracted from the ribs of a Neanderthal infant, one of the 
last of its kind, supports the thesis that these hardy, beetle-browed people 
left little or no genetic legacy in today's populations. 

Even though Neanderthals perished long ago, the surprising retrieval of 
intact DNA, the second such sample to be recovered, has set biologists 
speculating that with further finds the genetics of this extinct human 
species could become quite well understood. 

The two DNA retrievals, both suggesting that Neanderthals were a separate 
human species, were separated in time by a startlingly contradictory finding 
made last June. After studying the remains of a thick-set boy recovered from 
a cliff-side grave in Portugal, considered a final hold-out of the 
Neanderthals, paleoanthropologists said that the human child had strong 
Neanderthal features, and that this "refuted" the idea that modern humans had 
exterminated the Neanderthals without interbreeding. 

Neanderthals and their forebears occupied modern Europe from around 300,000 
years ago. They were adapted to the cold conditions of the ice age and had 
stocky bodies, thick bones and enormous strength. Though their stone tools 
seem similar to those of modern humans who started to enter Europe from Asia 
around 35,000 years ago, they ceased to flourish and abruptly disappeared 
throughout their home range around 28,000 years ago, leaving no clues in the 
archaeological record as to the reason for their extinction. 

Neanderthal DNA was first isolated three years ago, from the original bones 
first found in the Feldhofer Cave in the Neander Valley near Düsseldorf in 
1856. 

The finding was startling because no human DNA of such antiquity -- at least 
30,000 years old -- had been recovered and because it showed a pattern of DNA 
that was quite different from that of modern humans. 

Though the Feldhofer DNA was extracted with elaborate precautions, the 
finding was greeted with some reservation because it was a single result. 

Confirmation has now come from a second Neanderthal. 

The remains were recovered by a Russian expedition from the Moscow Institute 
of Archaeology to the Mezmaiskaya Cave in the Caucasus, to the northeast of 
the Black Sea. They belonged to a Neanderthal infant less than 2 months old, 
too young for the sex to be determined from the bones. The bones were dated 
by the carbon isotope method to 29,000 years ago, making the infant among the 
last generations of the Neanderthals. 

A sample of the infant's ribs was made available by the Russian researchers 
to Dr. William Goodwin of the Human Identification Center at the University 
of Glasgow. Dr. Goodwin works on paternity cases and plane-crash victim 
identification, and studies ancient DNA as a sideline. 

Dr. Goodwin and his Russian and Swedish colleagues report in this week's 
issue of Nature that the DNA sequence from the Mezmaiskaya Cave is 3.5 
percent different from that of the Feldhofer Cave Neanderthal, suggesting a 
considerable genetic diversity within the Neanderthal population. 

But the two Neanderthal DNA sequences are very different from those of modern 
humans, Dr. Goodwin and his colleagues say. 

Based on the rate at which DNA changes over time in living organisms, Dr. 
Goodwin calculated that the two Neanderthals last shared a common ancestor at 
least 150,000 years ago, a date that matches the first fully Neanderthal 
remains, and that the Neanderthal and modern human lineages split some 
600,000 years ago. 

Two paleoanthropologists who favor the Neanderthal-human assimilation theory, 
Dr. Fred Smith of Northern Illinois University and Dr. Erik Trinkaus of 
Washington University in St. Louis, said they did not dispute the new DNA 
analysis but noted that it did not completely rule out the possibility of 
some interbreeding. Dr. Smith said the new DNA data was "incredibly important 
and significant" and "certainly strengthens the fact that there is quite a 
gap between Neanderthals and recent humans in terms of mitochondrial DNA." 

Mitochondrial DNA, inherited from the egg cell alone and thus through the 
maternal line, is far more plentiful and likely to survive than the DNA of 
the nucleus; both Neanderthal samples were of the mitochondrial type. 

But Dr. Smith and Dr. Trinkaus, who are experts on the Neanderthals, believe 
that there was some interbreeding on the evidence of the Portuguese boy with 
Neanderthal affinities. 

Other anthropologists think the boy was just a "chunky" human lad who in any 
case lived far too many generations after the last Neanderthal had died for 
any evident influences to be expected. 

"It's got one feature that is arguably Neanderthal -- the shortness of length 
between the knee and ankle -- and even that is not striking," said Dr. 
Richard Klein, an archaeologist at Stanford University. 

Dr. Smith and Dr. Trinkaus say that even though Neanderthal DNA differs from 
that of modern people, it might be more similar to that of their human 
contemporaries, the Cro-Magnons. 

Curiously, no DNA has yet been recovered from very ancient Homo sapiens 
fossils. 

Dr. Klein agreed that new efforts should be made to retrieve Cro-Magnon DNA, 
though he said he expected it would prove similar to that of modern humans, 
sewing up the case that the Neanderthals were replaced. 

The factors that allow DNA to be preserved for thousands of years are not 
well understood. "Even with two bodies in the same grave, the level of 
preservation can vary considerably," Dr. Goodwin said. 

He thinks that something about the limestone cave may have favored the 
durability of the Caucasus Neanderthal DNA. 

If the reasons for preservation were better understood, DNA experts would 
know which precious museum specimens were worth sampling and which to leave 
alone.