Re: Man's best friend shares most genes with humans

From: Pim van Meurs <>
Date: Fri Dec 09 2005 - 12:41:33 EST

Todd Pedlar wrote:

> Michael Roberts wrote:
>> Pim
>> If you have genes in common with dogs you may be dog-like. That is
>> you might be friendly affectionate loyal etc. Maybe that is what
>> Janice is afraid of!
>> Our previous dog often looked at us with the same expression as
>> Princess Diana, so we always said there was a genetic similarity and
>> relationship!
>> Why get worried if we share behaviour or genes with animals? We do
>> and that is the end of it. All it does is to prove Darwin right, but
>> I have known that for years!
> This is another example of claims that I find lacking. "All it does
> is prove Darwin right".
> It reminds me a great deal of the "proofs" that my students often give
> on quantum mechanics
> homeworks that aren't "proofs" but rather demonstrations of
> consistency of the conclusion with
> the premises, which are not the same (nor are they sufficient), as
> "proof" of the demonstrated
> concept.

It does take some work to reach the conclusion but let's for the moment
focus on a hypothetical situation where the dog genome were shown to
have nothing in common with the human genome. Now that would be quite a
problem for evolutionary theory. That dogs share some similarity with
other mammals like us is indeed shows strong evidence for common descent.

> I'm not trying to be obtuse - nor am I making any claims at all about
> Darwin or
> not...I'm just looking at things that are commonly claimed and
> questioning the validity of
> the statements. What I'm trying to do (as I noted before in a post
> that I made, which
> subsequently I had no time to follow up on) is point out where I think
> the rhetoric falls short
> of logical validity.
> Here are two pictures of some objects:
> Now since a very large percentage of these two animals
> are identical, I guess that observation proves that they
> evolved from a common ancestor.

Just two 'minor' problems. No known (natural) mechanisms of inheritance,
no known (natural) mechanism of variation. I'd say that phylogenetically
these two have little in common other than some very basic foundation
blocks. In other words, the analogy is pretty poor.

> One of the other claims made in the quoted snippet from Pim is
> that 5% of the genes in both man and dog haven't changed at all
> for 100 million years. On what basis is such a claim made? Is it
> on the same basis as the claim that dogs and humans branched off
> 95 million years ago?

The claim that they have not changed at all is made on a comparisson
between the human genome and the dog genome. I doubt that the branching
date is determined from the common part.

 From one of the papers

Comparison between human and dog shows that approx5.3% of the human
genome contains functional elements that have been under purifying
selection in both lineages. Nearly all of these elements are confined to
regions that have been retained in mouse, indicating that they represent
a common set of functional elements across mammals.

But we are closer to the mouse

All mammals, at one point, had a common ancestor. But dogs are known to
have diverged toward an independent species about 95 million years ago.
The mouse and humans both diverged about 87 million years ago, making
mice closer to humans in time.

"We are much closer to the dog than to the mouse in terms of our gene
content and structure," said Venter. "But if you do the evolutionary
tree, we are on the same linage as the mouse. The mouse is evolving at a
much faster rate."

The dates are from

Placental mammal diversification and the Cretaceous-Tertiary boundary by
Springer et al PNAS | *February 4, 2003* | vol. 100 | no. 3 | *1056-1061

The relevance of the dog genome is that it helps us understand human
evolution and human illnesses:

The dog is similarly important for the comparative analysis of mammalian
genome biology and evolution. The four mammalian genomes that have been
intensely analysed to date (human^20,
, chimpanzee^23
, mouse^24
and rat^25
) represent only one clade (Euarchontoglires) out of the four clades of
placental mammals. The dog represents the neighbouring clade,
. It thus serves as an outgroup to the Euarchontoglires and increases
the total branch length of the current tree of fully sequenced mammalian
genomes, thereby providing additional statistical power to search for
conserved functional elements in the human genome^24,
. It also helps us to draw inferences about the common ancestor of the
two clades, called the boreoeutherian ancestor, and provides a bridge to
the two remaining clades (Afrotheria and Xenarthra) that should be
helpful for anchoring low-coverage genome sequence currently being
produced from species such as elephant and armadillo^28

Here we report a high-quality draft genome sequence of the domestic dog
(Canis familiaris), together with a dense map of single nucleotide
polymorphisms (SNPs) across breeds. The dog is of particular interest
because it provides important evolutionary information and because
existing breeds show great phenotypic diversity for morphological,
physiological and behavioural traits. We use sequence comparison with
the primate and rodent lineages to shed light on the structure and
evolution of genomes and genes.
Notably, the majority of the most highly conserved non-coding sequences
in mammalian genomes are clustered near a small subset of genes with
important roles in development.
Analysis of SNPs reveals long-range haplotypes across the entire dog
genome, and defines the nature of genetic diversity within and across
breeds. The current SNP map now makes it possible for genome-wide
association studies to identify genes responsible for diseases and
traits, with important consequences for human and companion animal health.
Received on Fri Dec 9 12:45:36 2005

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