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Richard Dawkins mentions in his book The Greatest Show on Earth that dogs are exactly similar to both humans and chimps. Supposing that a cell contains the genetic similarity between 2 species, he says

The human/dog cell should have an identical resemblance score to the chimpanzee/dog cell because humans and chimpanzees have exactly the same degree of relation to dogs. It should be identical, too, to the monkey/dog cell and the lemur/dog cell. This is because humans, chimpanzees, monkeys and lemurs are all connected to the dog via their common ancestor, an early primate (which probably looked a bit like a lemur)

He later says that this will be found within "statistical margins of error".

Because the common ancestor of both chimps and humans was more similar to chimps than to humans, it stands to reason that chimps will be more genetically similar to the common ancestor than humans. Therefore (not a direct therefore), dogs and humans can't be exactly similar as dogs and chimpanzees are, even theoretically. Humans and apes are even more dissimilar. Therefore ape/dog cell will not be exactly same value as the human/dog cell.

Please explain where I am wrong.

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Is this premise of your argument correct? - "the common ancestor of both chimps and humans was more similar to chimps than to humans". Since chimps and humans have been evolving for the same amount of time since they diverged, why do you think that chimps are closer to that ancestor than are humans? –  Alan Boyd Oct 9 '13 at 14:43
    
I agree a lot with what Alan said. If I have time I will come back later with a full answer. At the moment you should read up on genetic distance, which is what we are talking about here. I doubt if you were to actually calculate it, they would be identical, but you have to go back far enough in mammalian history to a shared ancestor of dogs and humans/chimps. The assertion is that the most recent shared ancestor between all three was the same species. –  Atl LED Oct 9 '13 at 14:51
    
Physical similarity doesn't guarantee genetic similarity, I understand, but it seems a little intuitive that some genes from a common ancestor pass unchanged in a descendant A that had a similar environment, while changing in another B, that had a different environments, thus making it possible that A will be more genetically similar to its ancestor than B. –  Daud Oct 9 '13 at 15:04
    
maybe you could expand the dawkins quote? it doesn't really make sense to me. chimps are much more closely related to us than dogs by most measures. –  shigeta Oct 9 '13 at 16:56
    
expanded the Dawkins quote –  Daud Oct 9 '13 at 19:30

2 Answers 2

Dawkins is overgeneralizing. Genetic distance is a fairly new field, and a heated topic, since your answer depends upon which genes you are comparing. If you picked ONLY strongly-conserved genes for your genetic distance comparison, then you'd find that humans, bonobos, dogs, mice, mosquitos, shrimp, and bakers' yeast are all equally distant (and that the distance is small). But if you pick ONLY very weakly-conserved genes for your genetic distance comparison, you can get crazy results -- humans are more closely related to yeast than to horses, for example. (Creationists have had a heyday making fun of some early genetic distance studies that, in retrospect, had poorly-chosen genes.) So biologists doing genetic distance comparisons try to pick genes that are common to many species, and that have some drift to them, but not so much that the answers are obviously goofy. Another problem that has arisen is that sometimes an entire gene in several species appears to have been obtained from a very dissimilar species, in a different phylum or kingdom even. (Current theory is that this is the work of viruses.) The "tree of life" paradigm might need to be changed to the "web of life." Needless to say, there's still a lot of argument about which (and how many) genes to pick for genetic distance studies.

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Yes and no. Yes their DNA, like every living thing’s DNA, is made of the same building blocks of A’s, T’s, G’s, and C’s. But their DNA isn’t exactly alike. All those A’s, T’s, G’s, and C’s are put together in different orders for dogs and people. You have to understand that 4% with chimps is a difference of actually 35 million single nucleotide differences and ∼90 Mb of insertions and deletions. With a dog only 25% matches up perfectly with a human. I think what he was saying was that all living matter has a common ancestor. From fruit fly to human being according to macro evolution we all came from the same ancestor.

http://genetics.thetech.org/ask-a-geneticist/dog-vs-human-dna http://genome.cshlp.org/content/15/12/1746.long

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