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Author Topic:   Human Evolution (re: If evolved from apes, why still apes?)
Taq
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Posts: 9972
Joined: 03-06-2009
Member Rating: 5.5


Message 116 of 128 (583755)
09-28-2010 7:15 PM
Reply to: Message 111 by barbara
09-28-2010 9:29 AM


Re: where to go?
Unfortunately all my research on the subject is producing radically different conclusions, DNA percentages are different, time lines is different, common ancestry is different, etc. It seems no one in the scientific community can agree with each other on the results.
New evidence and new methodologies allow us to make more accurate conclusions. If scientists had to wait for the perfect methodology and results to come around nothing would get done.
You mention DNA percentages. The accuracy of this number has always been a reflection of the technologies and methodologies used. One of the earliest methods used to measure the DNA homology between humans and other apes was hybridization, the ability of similar DNA sequences to stick to one another. Of course, this only gives a gross estimate for DNA homology. The advantage of this method is that it is able to probe the entire genome at once.
Of course, DNA sequencing is the most accurate method. However, up until recently DNA sequencing was labor intensive, produced a lot of data that had to be crunched by either humans or (relatively) primitive computers. Back in the day I actually poured sequencings gel and then read the sequence visually using 32P terminally labelled PCR reactions. The gel would look like this:
You would have to run 4 PCR reactions for each DNA sequence and read the gel visually, recording the data yourself either on a notepad or into a computer. We used to run 16 lane gels so we could only look at 4 DNA sequencing runs at a time.
Because of this it was slow going when trying to sequence an entire genome. So what did people do? They compared sequences from small portions of the genome and extrapolated to the whole genome. Of course, this can only produce an estimate and not a true percentage of homology.
It wasn't until DNA sequencing technology came of age that whole genome sequencing became doable. New automated technology can run thousands of sequencing runs in parallel, and they use dyes instead of radioactively labelled nucleotides which allows them to run a single PCR reaction for an entire sequencing run. These automated sequencers are also linked up to huge computer networks that crunch all of the data for you. On top of that, 454 Life Sciences developed what they call pyrosequencing which speeds up DNA sequencing even faster, and it only requires a single strand of DNA to do it. 454 sequenced an entire human genome (that of the infamous James Watson) in just 3 months where the Human Genome Project took two 13 years to do the same thing.
So to make a long story short, conclusions are only as good as the methodologies that support them. That is what peer review focuses on most is methodology. What they look at second is if the conclusions made by the authors go beyond what the methodology can show. Any well written paper will qualify the conclusions with reference to how accurate the methodology is. If you read closely you can pick this out.
Edited by Taq, : No reason given.

This message is a reply to:
 Message 111 by barbara, posted 09-28-2010 9:29 AM barbara has replied

Replies to this message:
 Message 117 by barbara, posted 10-04-2010 1:30 PM Taq has replied

  
Taq
Member
Posts: 9972
Joined: 03-06-2009
Member Rating: 5.5


Message 118 of 128 (584928)
10-04-2010 6:01 PM
Reply to: Message 117 by barbara
10-04-2010 1:30 PM


Re: where to go?
I just read the Chimpanzee genome project and if you go there you will find is there are several differences between us and chimps. A 30% difference that covers all areas.
"Single-nucleotide substitutions occur at a mean rate of 1.23% between copies of the human and chimpanzee genome, with 1.06% or less corresponding to fixed divergence between the species."
"Orthologous proteins in human and chimpanzee are extremely similar, with 29% being identical and the typical orthologue differing by only two amino acids, one per lineage."
Initial sequence of the chimpanzee genome and comparison with the human genome | Nature
Do you understand the difference between these comparisons? While 70% of the proteins are different in amino acid sequence they only differ by 1 or 2 amino acids between the proteins, on average. So if the average protein is 500 amino acids we are talking about a tiny change between proteins, even if 70% of the proteins are different by a tiny amount.
Your confusion seems to stem from assuming all percentages can be directly compared with each other. They can't. You need to understand the context.

This message is a reply to:
 Message 117 by barbara, posted 10-04-2010 1:30 PM barbara has not replied

  
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