Fossils and DNA

[jbernar6]

Fossils can be dated with a fairly high degree of accuracy and precision using radiometric methods.

Dating of lineage divergence events using DNA sequence divergence data is more problematic, but

such data consistently give lineage divergence dates that are tens of millions of years older than dates from

the fossil record.

 

How can these differences be reconciled?

 

Thanks!

[CharonY]

They are mathematical models based on current available sequences and include factors like e.g. mutation rates.

[jbernar6]

Thanks for answering.

 

I'm sorry if I'm beating a dead horse, but what exactly accounts for the differences?

[swansont]

Fossils can be dated with a fairly high degree of accuracy and precision using radiometric methods.

Dating of lineage divergence events using DNA sequence divergence data is more problematic, but

such data consistently give lineage divergence dates that are tens of millions of years older than dates from

the fossil record.

 

How can these differences be reconciled?

 

Thanks!

 

Do you have an example or two in mind? The few with which I am familiar have no such discrepancy.

[CharonY]

Yeah, that would be good. I kind of misread the OP- I kind of thought the question was what the difference in establishing the lineages were (sucks not to be able to read).

Differences are to be expected, of course, but "consistent" differences are unlikely.

[jbernar6]

Yeah, that would be good. I kind of misread the OP- I kind of thought the question was what the difference in establishing the lineages were (sucks not to be able to read).

Differences are to be expected, of course, but "consistent" differences are unlikely.

 

What accounts for such differences?

[CharonY]

Please provide an example that we may discuss.

[jbernar6]

Please provide an example that we may discuss.

 

That's the thing, I do not have a specific example. My professor mentioned it in class and I was curious of why there would be differences. In general terms, are there reasons for this? Or possibly you have an example in mind. Sorry I'm not being very much help.

[john5746]

http://www.geotimes.org/dec07/article.html?id=feature_ancientlife.html

 

Fossils are snapshots, so you are never going to get the "oldest" one. Also, on the molecular side, it is based on estimation of mutation change, so the farther you go back, the wider the date range.

[Mokele]

Some of it may be due to departure from the assumption of neutrality - many of the 'molecular clock' estimates assume the sequence in question isn't under selection, and that may not be true.

[jorge1907]

What uninformed clow3ns - you can't get DNA from fossils you idiots!

[iNow]

What uninformed clow3ns - you can't get DNA from fossils you idiots!

 

Time to look in the mirror, friend. You may have missed this one, with it being 10 years old, and all:

 

 

http://www.eurekalert.org/pub_releases/2007-07/uoc-fdi062207.php

Scientists have extracted and amplified DNA from 19,000-year-old sloth dung from Gypsum Cave in Utah, 18 miles east of Las Vegas, Nev. The DNA comes from plants the animal ate and from cells that lined its digestive tract.

 

The researchers are the first to successfully use what's called the PCR technique to analyze DNA in coprolites, or ancient feces.

 

 

Wait. What's that? You want something more recent? Okay.

 

http://palaeoblog.blogspot.com/2007/01/extracting-dna-from-fossils.html

An extensive study of around 250 fossil bones from 600 to 50 000 year old herbivores showed that mitochondrial DNA from freshly excavated, untreated fossil bones was amplified with a success rate of 46%.

 

 

 

Looking for something less for the layman, and more of the peer reviewed flavor? Okay, I've got that, too:

 

 

 

http://www.pnas.org/content/102/39/13783.full

We demonstrate that relatively well preserved DNA is occluded within clusters of intergrown bone crystals that are resistant to disaggregation by the strong oxidant NaOCl. We obtained reproducible authentic sequences from both modern and ancient animal bones, including humans, from DNA extracts of crystal aggregates. The treatment with NaOCl also minimizes the possibility of modern DNA contamination. We thus demonstrate the presence of a privileged niche within fossil bone, which contains DNA in a better state of preservation than the DNA present in the total bone. This counterintuitive approach to extracting relatively well preserved DNA from bones significantly improves the chances of obtaining authentic ancient DNA sequences, especially from human bones.

 

 

There are plenty more which I could easily share in case you haven't been embarrassed enough yet for making such an ignorant and (what was that word you used?...) uniformed comment.