Re: [asa] How big a deal is homology?

From: Terry M. Gray <>
Date: Tue Mar 27 2007 - 16:26:34 EDT


How big of a deal is homology in paternity testing? Or DNA
fingerprinting? Or establishing the human family tree? Or the dog
family tree?

What is the explanation for homology if it's not common descent? Why
isn't it 100%? Why does the degree of homology seem to be less as the
putative evolutionary divergence increases?

I will grant that using homology to detect evolutionary relationships
presupposes common ancestry (just as it does in paternity testing,
DNA fingerprinting, pedigree analysis (and manuscript transmission)).
But the mechanisms of transmission and change of genetic material are
known. It's not unreasonable (unless you have some philosophical or
theological or other reason not to accept it). However, the trees
generated by analysis of homologies are not presupposed and the
results are remarkably consistent with an evolutionary interpretation.

If evolution didn't happen, then God went through a lot of effort to
make it look like it did.


On Mar 27, 2007, at 10:09 AM, Brent Foster wrote:

> This is a question for those on the list who know more molecular
> genetics than I do (almost everyone!). Now that the human genome
> has been sequenced, as well as that of several other organisms,
> sequences can be compared and checked for similarity. Much has been
> made of the 95 odd percent similarity between the genomes of humans
> and chimps. And of course the 80 odd percent similarity between
> mice and humans. Anti-evolutiuonists point out that the similarity
> is only 95 or so percent, not the 98% once claimed. Ha! And of
> course mice are even less similar. But isn't the problem that there
> is any similarity at all? Aren't family relationships demonstrated
> by matching identical sequences of DNA that are long enough to rule
> out coincidence? And aren't these same types of similarities found
> linking different species, genera, families etc, such as humans,
> chimps and mice? Maybe I'm demonstrating my ignorance of molecular
> genetics. Does 95% similarity between human and chimp DNA mean !
> that 95% of the sequences are similar? I ask because I am involved
> in discussion with someone who is skeptical of DNA comparisons.
> Brent
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Terry M. Gray, Ph.D.
Computer Support Scientist
Chemistry Department
Colorado State University
Fort Collins, CO 80523
(o) 970-491-7003 (f) 970-491-1801

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Received on Tue Mar 27 16:27:12 2007

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