This is a continuation of last week's installment in my Evidence for Evolution series. Since this post builds directly on concepts discussed last week, I highly recommend that you read last week's thread carefully before looking at this one. It is here:
http://www.jehovahs-witness.com/6/87781/1.ashx
Previous articles in this series are here:
Retroviral sequences: http://www.jehovahs-witness.com/6/86797/1.ashx
Cytochrome c: http://www.jehovahs-witness.com/6/87238/1.ashx
What evolution is not: The role of randomness: http://www.jehovahs-witness.com/6/87711/1.ashx
Primary sources for this article:
Hominids and mtDNA: http://www.talkorigins.org/faqs/homs/mtDNA.html
What is Mitochrondial Eve?: http://www.talkorigins.org/faqs/homs/mitoeve.html
Paleoanthropological Discovery Timeline: http://www.talkorigins.org/faqs/homs/recent.html
Overview of Neandertals: http://www.answers.com/topic/neandertal
Refutation of Common Creationist Arguments Regarding Neandertals: http://www.talkorigins.org/faqs/homs/a_neands.html
Neandertals Were Not Our Ancestors: http://www.psu.edu/ur/NEWS/news/Neandertal.html
Neandertals
Because there are a lot of popular misconceptions about Neandertals, throw out everything you think you know about them unless you have actually done research. The reality is probably significantly different than you imagine.
The first Neandertal was discovered in 1856 in the Neander Valley in Germany (tal = valley in German). Interestingly, this was three years before Darwin published his famous book. As more and more Neandertals were found, we learned that these people, although strikingly similar to humans, were significantly different from modern humans in anatomy. Some of the major differences are:
- Pronounced brow ridge
- No chin
- Slightly larger brain cavity (10% larger)
- Differently shaped ear labrynths
- Shorter and considerably stouter than modern humans (bones are 50% thicker on average that modern humans)
- Barrel-shaped rib cage
A visual comparison of the skulls of humans with Neandertals should be sufficient to demonstrate the differences.
Images from the University of Texas (Neandertal http://www.utexas.edu/courses/denbow/labs/homoneand.htm and Homo sapiens http://www.utexas.edu/courses/denbow/labs/homosap.htm).
At first, some suggested that these were just humans that suffered from some disease or environmental problem. However, a couple things make this a poor explanation. First, there are no diseases that have been observed to create such effect in humans. Second, the traits described above are observed in all discovered Neandertals. To date, we have unearthed more than 400 Neandertal specimens.
If they weren't modern humans, then, were they just some sort of advanced ape? No. The evidence is clear that they had an advanced stone-tool culture, controled fire, and had advanced weapons. The Answers.com source cited above says:
There is good evidence that they routinely constructed a variety of stone implements. The Neanderthal (Mousterian) tool case consisted of sophisticated stone-flakes, task-specific hand axes, and spears. Many of these tools were very sharp: some had a cutting edge sharper than a surgeon's scalpel.
The similarity to humans on one hand but the obvious differences on the other striking. The creationist sites answersingenesis.com and biblestudy.org both assert that he was fully human, and speculate about old age, disease, environmental factors, or closeness to perfection (!?) being the cause of his different anatomy.
From biblestudy.org:
Neanderthal man was a direct descendant of Adam. He was therefore closer to the creation than we are.
--http://www.biblestudy.org/basicart/neander.html
Answersingenesis.com says:
Neandertal fossils are all post-Flood, so these bones are believed to represent just one more group of people which split off from other groups following the Babel dispersion.
--http://www.answersingenesis.org/creation/v25/i4/neandertal.asp
If you take a look at these sites, keep in mind that there are several patently false characterizations of what evolution predicts for Neandertal morphology, as well as blatant fabrications about the science (compare the assertion that "Neandertal fossils are all post-Flood" with the next paragraph).
The geologic record puts Neandertals in Europe from about 230,000 years ago to about 29,000 years ago. Anatomically modern humans are found in Africa from about 150,000 years ago, showing that humans lived at the same time as this sister species.
Okay, so aside from disputes about exactly when Neandertal Man lived and how closely he was related to Adam, we are basically in agreement: Neandertals were real, they were clearly different in significant ways from humans, while retaining much of what we consider to be human, and they lived at the same time as modern humans.
Mitochondrial DNA and Neandertals
In our last installment, we reviewed mitochondrial DNA, or mtDNA for short. Recall that mtDNA is passed only from the mother, and it changes only rarely (unlike nuclear DNA), so it allows us to trace matrilineal ancestry. On the basis of mitochondrial DNA evidence, we know that all humans are related through a common female ancestor who probably lived about 170,000 years ago. Because this most recent common female ancestor is called Mitochondrial Eve, creationists are fond of suggesting that mtDNA supports the Bible.
Here's where it gets interesting. Because mitochondrial DNA is much more abundant than nuclear DNA (about 500-1000 copies per cell) and it is much shorter (about 16,500 base pairs compared to 4.8 billion), it is much easier to extract and study. If we could get our hands on some Neandertal mtDNA, we could surely learn a great deal about how they fit in with the human family, if at all.
First, let's consider what we should expect if Neandertals are related to humans, and especially if they are very recently related, as creationists suppose. If Neandertals were "just one more group of people which split off from other groups following the Babel dispersion" (a mere 4000 years ago, supposedly), we would expect that their mtDNA would be exceedingly similar or identical to ancient human mtDNA, since all humans supposedly bottlenecked through three matrilineal lines which would have interbred profusely. Neandertal mtDNA should also show clear relatedness to modern human mtDNA.
On the other hand, if Neandertal mtDNA is grouped together with that of other Neandertals but does not show any clear relation to that of modern humans, and especially if it shows no clear relation to ancient human samples, it would mean that Neandertals are not in our ancestry but represent a separate line of hominid, a sister species to humans.
In July 1997, the first mitochondrial DNA was successfully recovered from a Neandertal specimen. mtDNA was successfully extracted from two other Neandertals, including a baby, in 1999 and 2000, confirming the results from the first. What have we learned from the comparison of the mtDNA from these four Neandertals with humans?
When the three Neandertals are compared with modern humans, all three of them cluster together, and apart from all modern humans. This conclusion is reinforced by a study by Knight (2003). Knight excluded from the comparison sites in the mtDNA genome which are known to have mutated more than once, and which are therefore poor indicators of phylogenetic relationships. His study strongly confirmed earlier ones showing deeply divergent histories for modern human mtDNA lineages and the known Neandertal ones.
-- http://www.talkorigins.org/faqs/homs/mtDNA.html
Further, in 2004 mtDNA was sequenced from four more Neandertal specimens, as well as five early humans. Once again, the Neandertal mtDNA was distinct from the human mtDNA. The team found no evidence of gene flow between the two populations.
What does this mean? Just as mtDNA from humans points to common ancestor about 170,000 years ago, mtDNA shows that Neandertals do not share that Mitochondrial Eve with humans.
Neandertals are not closely related to humans (at least not in the sense of being our ancestors). Humans and Neandertals likely diverged 500,000 to 600,000 years ago and then lived chronologically side-by-side, as sibling species which did not or could not interbreed.
The key to understanding this is that, even if we throw away the dates (since creationists obviously have a built-in problem with dates higher than 6000 years), the evidence is clear that all humans are related through a common ancestor, and that Neandertals represent a completely seperate line. Sister species living side-by-side humans are expected in evolutionary theory, but they obviously present a major impediment to a literal interpretation of Genesis.
SNG
(Edited to correct typing mistakes)