Evidence for evolution

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Is it a matter of looking at an earlier fossil and a later fossil and determining that they are closely related according to the DNA? Something like that?

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This has been done successfully but only for very shallow depths of time i.e. the oldest reliable fossil DNA sequences are about 80,000 years old. So one cannot look at fossils millions of years old and do a direct comparison. But you can for example do comparisons of DNA sequences among living species that are thought to be closely related or distantly related. Evolution would predict, that for a locus under weak or no selection that the gene would be more simlar among the closley related species (since less time has passed since they diverged and less mutations would have had time to occur) and the same locus would be much more divergent among more distantly related species. Up to a point, the accumulation of mutations can be "clocklike" and calibrated to a fossil date or known divergence event to determine the time of the split. But even without this, one can trace the relationships among the organisms in the form of a tree by the sequence similartiy or dissimilartiy...it is not so much different from morphology only the characters are base changes at the DNA level rather than say tooth differences among mammals. At some point, whole genome sequences will be compared among most species which will be really interesting in determining among group relationships.

Sure..but strongly conserved sequences are not particularly useful in all levels of phylogenetic or relatedness analysis. If I look at a sequence that is identical between the two groups I am interested in, I am stuck other than to say they both shared a common ancestor with that had the gene or it arrived by horizontal transfer recently. The conservation indicates common ancestry but the variation allows you to tell who is more closely related to who.

hi r,
Nucleic acids fall apart pretty quickly. In fact, most of the damage occurs shortly after death and not because of the long time the sample has been buried. For example, there is no correlation between age of a bone and the quality of DNA you can retrieve from it except at the upper boundaries. What I mean by this is I have mammoths that are 4,000 years old that yield no DNA or really badly degraded DNA whereas I have samples that are 13-20,000 years old that yield lots of DNA and are easy to work with. In the literature, this seems to also hold true. The upper bound is that nobody has reproducible DNA sequences from samples over 100,000 years old so that is about the only age-degradation correlation that holds up.When an organism dies, most of the organelles break apart releasing digestive enzymes which destroys proteins and DNA. RNA and DNA both hydrolyze easily (it takes a lot of energy derived from food to maintain a cell). In addition, there are lots of bacteria and fungi that find dead things very tasty and so a corpse will be consumed meaning even more nucleic acid destruction...think of a road kill...the first day you drive by it, it looks like an animal...a week or so later it may just be a mass of unidentifiable bone and some meat attached... In the case of frozen mammoths, the temperature was unlikely stable i.e. they freeze thawed and are like freezer burned meat...yet again, extra damage to biomolecules.In testing modern DNA, you either have freshly killed samples or take blood, hair, swabs from the mouth,cell culture or even feces and immediately prepare the DNA or freeze the samples in liquid nitrogen stopping the degradation process for a while...so working with modern tissues is really much easier since you can get a lot of good quality DNA.Hope this helped.

hi cmanteuf
The problem with Ed Golenberg's magnolia work, all of the amber studies, and the one published dinosaur DNA study is that none of the studies could be reproduced. The dinosaur study fell apart when it was determined that the sequence was actually a human mtDNA pseudogene and not a sequence from the fossil i.e. contamination. A systematic study of amber failed to detect DNAAustin JJ, Ross AJ, Smith AB, Fortey RA, Thomas RH. Related Articles, Links
Problems of reproducibility--does geologically ancient DNA survive in amber-preserved insects?
Proc R Soc Lond B Biol Sci. 1997 Apr 22;264(1381):467-74.In one particular case, the amber work appears to have been fraudulentGutierrez G, Marin A. Related Articles, Links
The most ancient DNA recovered from an amber-preserved specimen may not be as ancient as it seems.
Mol Biol Evol. 1998 Jul;15(7):926-9. No abstract available.Golenberg's work is not fraudulent...but he himself never reproduced it and considering the inability of anyone else to confirm the results of any really ancient DNA study, it is not currently accepted as bona fide sequence.After all, it is hard enough to get DNA out of less ancient samples so the standards for really old samples has to be significantly higher.

It is not actually a gap in communication. Several creationist and IDist organizations claimed that the ToE and abiogenesis are the same thing. Scientists did not initiate the claim. Thus it is not miscommunication. It is misrepresentation of science by non-scientific organizations.If you claim I own a dog when I never made the claim myself, that is not a miscommunication of ideas.

I'll give you that. A lot of popular science shows are crap. Including a lot of the BBC and Discovery Channel shows that go more for special effects and story than actual scientific content.The problem is that most scientists interact with other scientists. Only a small subset interact with the general public on any regular basis...and even when there is interaction with the media..they often get the stories wrong...a newspaper just covered some of my research and misreported a few facts including giving me the wrong nationality and claiming my colleague comes from somewhere else as well...even though we supplied him with written text.This message has been edited by Mammuthus, 12-15-2004 10:36 AM

Many of the science shows are info-tainement and highly speculative. I am particularly thinking of "Walking with Dinosaurs" where they attributed all sorts of social behaviors to each dinosaur they showed as if it were fact.In a scientific paper you can easily distinguish between the data/evidence that has been gathered, the conclusions the authors draw from the data and any speculative extrapolations they might propose...and you are free to repeat the work or analyze the data yourself. This is obviously not the case in a tv show or popular book on science.

Unfortunately, I can't access the article either (I am in a virology institute and we don't have subscriptions to the botany lit..I can order it but it won't get to me before January). However, I already see two problems in the abstract. 1) They are not confirming the sequence from the same sample as Golenberg analyzed. This is part of what killed off amber as a few groups reported they had sequences from different pieces. But nobody could reproduce the work (one group tried and failed). Austin did a systematic approach and failed. 2) The lengths of sequence they report are outrageous. I had a bear of a time recently generating 1,180 bp of cyt b from a muskox sample that was 18,000 years old. They get larger fragments from a sample millions of years old?The other problem is that groups such as Svante Pbo's have done everything from amino acid racemization studies to DNA analysis from Clarkia and came up with absolutely nothing.Until the same sample can be analyzed independently and the sequence reproduced, it will be met with a great deal of skepticism.Althought the title and some of the recommendations in the article are crap, the overall scheme of authentication of ancient DNA in this article have to be met for the sequeunce to be taken seriouslyCooper A, Poinar HN. Related Articles, Links
Ancient DNA: do it right or not at all.
Science. 2000 Aug 18;289(5482):1139. No abstract available.