Prime Time Replay:
Anne Stone, Ph.D
on the DNA studies of Neaderthals
and the "Ice Man"
MsgId: *infinities(131)
Date: Sun Aug 10 21:47:01 EDT 1997
From: Melanie At: 204.164.64.205
This evening, August 10, we are happy to welcome Anne Stone, Ph.D., of the Laboratory of Molecular Systematics and Evolution, Department of Ecology and Evolutionary Biology at the University of Arizona. Dr. Stone was one of the scientists who contributed to the recent revelatory research on the DNA of a 30,000-year-old Neandertal specimen. The findings from which have rocked the anthropology establishment. Dr. Stone will talk with us about the Neandertal project in particular, and her work in ancient genetics -- including studies on the Ice Man -- in general.
MsgId: *infinities(132)
Date: Sun Aug 10 21:48:59 EDT 1997
From: Anne At: 146.186.95.78
Hello, thanks for inviting me.
MsgId: *infinities(133)
Date: Sun Aug 10 21:52:39 EDT 1997
From: Melanie At: 204.164.64.205
Dr. Stone and audience, welcome. Since mid-July when the latest edition of Cell came out, the popular press has been full of news of the work of Dr. Stone and her colleagues, most particularly of the team leader, Dr. Svante Paabo of Ludwig Maximillian University in Munich, Germany. Before we get into the specifics of the new discoveries, Dr. Stone, could you tell us a little bit about what we know about Neandertal -- the team spells it without the usual "h" in the Cell article.
MsgId: *infinities(134)
Date: Sun Aug 10 21:58:51 EDT 1997
From: Anne At: 146.186.95.78
The first Neandertal specimen was found in the Neander valley, Germany. Tal or Thal is German for valley but the h is silent and now they leave it out. The skeleton was found in 1856 and is somewhere between 30,000 and 100,000 years old.
MsgId: *infinities(135)
Date: Sun Aug 10 22:00:51 EDT 1997
From: Melanie At: 204.164.64.205
There are the usual jokes about Neandertal being a bit of a brute, but apparently they weren't as "unevolved" as they are often portrayed. What were these creatures like? What did they look like? Did they have a social system of any kind that we know of?
MsgId: *infinities(136)
Date: Sun Aug 10 22:07:30 EDT 1997
From: Anne At: 146.186.95.78
Neandertals had about the same brain size as we do. Typically they are described as very muscular with a stocky body build that would be adaptive in a cold climate. The most striking physical difference between Neandertals and modern humans would be the large brow ridges. The nature of the behavior of Neandertals is very controversial. Some archaeologists have suggested that they did not have complex symbolic behavior such as art or extensive trade networks.
MsgId: *infinities(137)
Date: Sun Aug 10 22:09:15 EDT 1997
From: Melanie At: 204.164.64.205
Can you tell us how and why you became involved in this recent important project with Dr. Paabo?
MsgId: *infinities(138)
Date: Sun Aug 10 22:17:24 EDT 1997
From: Anne At: 146.186.95.78
While I was a graduate student, I spent a year on a Fulbright scholarship in Dr. Paabo's lab in Germany. There I learned new techniques for working with ancient DNA. At the time, I was working on a project with a Native American population and I also participated in the Iceman project. Since he was very familiar with my work, Dr. Paabo sent a portion of the sample to Penn State for me to replicate the work done in his lab.
MsgId: *infinities(139)
Date: Sun Aug 10 22:18:30 EDT 1997
From: Melanie At: 204.164.64.205
How was the DNA extracted from such an ancient specimen?
MsgId: *infinities(140)
Date: Sun Aug 10 22:24:17 EDT 1997
From: Anne At: 146.186.95.78
The extraction technique is pretty standard. First you pulverize the bone or tooth using a freezer mill (or a modified paint shaker if you are on a budget). Then you soak the bone dust in a solution which breaks open the cell walls and releases the DNA. The next series of steps essentially separates the DNA from all the other stuff. The difficulty with ancient DNA is that there is not much DNA left so you have to use techniques that don't cause any more loss of DNA and you have to be very careful not to contaminate the sample with modern DNA.
MsgId: *infinities(141)
Date: Sun Aug 10 22:26:39 EDT 1997
From: Melanie At: 204.164.64.205
I understand mitochondrial DNA is used in these types of assays. What is mitochondrial DNA, and why is it particularly useful for testing?
MsgId: *infinities(142)
Date: Sun Aug 10 22:34:15 EDT 1997
From: Anne At: 146.186.95.78
Mitochondial DNA (mtDNA) is found outside the nucleus in the Mitochondria which are the energy producing organelles within each cell. Mitochondrial DNA is useful for population genetics because it is inherited through the maternal line and does not recombine. So if a woman has a daughter and a son, both inherit mtDNA from her but only the daughter will pass it on to her children. MtDNA is also useful because some regions have a high mutation rate that can provide information about recent evolutionary history. The mitochondrial genome has been completely sequenced in humans.
MsgId: *infinities(143)
Date: Sun Aug 10 22:36:40 EDT 1997
From: Melanie At: 204.164.64.205
Once extracted, what tests were run on the mtDNA? What was the team looking for?
MsgId: *infinities(144)
Date: Sun Aug 10 22:47:14 EDT 1997
From: Anne At: 146.186.95.78
I should mention that mitochondrial DNA is particularly useful for ancient DNA because it is present in 500-1000 copies per cell, and it is therefore easier to obtain. In order to examine the DNA we used the polymerase chain reaction (PCR) to make millions of copies of a particular region of the mtDNA. We chose the hypervariable region which is a noncoding segment that has been analyzed extensively in human population studies. We had to do many PCRs to look at the whole region since ancient DNA is degraded into small pieces. After PCR, we sequenced the region and compared the results with sequences from modern humans to examine the relationship between the two.
MsgId: *infinities(145)
Date: Sun Aug 10 22:49:59 EDT 1997
From: Melanie At: 204.164.64.205
What did you find when you compared that particular region of Neandertal mtDNA with the correspondoing region of human mtDNA?
MsgId: *infinities(146)
Date: Sun Aug 10 22:53:42 EDT 1997
From: Anne At: 146.186.95.78
It was quite different. When you compare the Neanderthal sequence to sequences from modern humans, there is an average of 27 differences. Modern humans typically differ by eight mutations, and there are about 55 differences between modern humans and chimpanzees.
MsgId: *infinities(147)
Date: Sun Aug 10 22:55:57 EDT 1997
From: Melanie At: 204.164.64.205
In terms of evolution, then, what does this large discrepancy between the human and Neandertal DNA say about the relationship between these species?
MsgId: *infinities(148)
Date: Sun Aug 10 23:06:53 EDT 1997
From: Anne At: 146.186.95.78
Well, that's the big question. It really depends on how much variation there was in Neandertal mtDNAs. If Neandertals were like modern humans (i.e. not that variable), then the data suggest that modern humans did not descend from Neandertals. If Neandertals had a much larger amount of variation then there is the possibility that they did contribute to modern populations. Since this is a sample of only one, we don't know what kind of variation was present. This one individual does suggest that the Neandertal and modern lineages split but we need to sample additional individuals.
MsgId: *infinities(149)
Date: Sun Aug 10 23:09:13 EDT 1997
From: Melanie At: 204.164.64.205
If it turns out that there was, in fact, no genetic mixing between modern humans and Neandertals, other than resolving a long-standing argument among scientists, why is this discovery so important?
MsgId: *infinities(150)
Date: Sun Aug 10 23:18:10 EDT 1997
From: Anne At: 146.186.95.78
This would indicate that more than one species of hominid was present fairly recently in evolutionary time and that some advantage allowed modern humans to outcompete the Neandertals. Some have concluded that such an advantage was the ability to use complex symbols such as language and art.
MsgId: *infinities(151)
Date: Sun Aug 10 23:21:35 EDT 1997
From: Melanie At: 204.164.64.205
Or the Internet perhaps? On that note, we'll end our discussion. I'd like to thank my guest, Anne Stone for sorting out the intricacies of this most interesting news from the worlds of anthropology and of genetics. And thanks to our audience for joining us on Infinities. Good night.
MsgId: *infinities(152)
Date: Sun Aug 10 23:23:07 EDT 1997
From: Anne At: 146.186.95.78
Thanks and good night.
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