About the genetic similarities of humans and chimps?

Question

I keep hearing that by examining the genome of humans and chimps have shown a 95-98 percent similarity. I have 2 questions about this:

1: Did the scientists us the ENTIRE genome of both humans and chimps in the study, or did they just take a chunk of each and estimate the overall similarity?

2: Did they contrast this comparison with another genome, for example a dog, horse or pig, to find whether the human/chimp genomes are MORE similar than other animals, or is it possible that ALL animals and humans have a 95-98 percent similarity that allows us to BE alive in the first place, while the remaining difference makes up the individual species?

FYI This isn't trying to prove anyone right or wrong, and yes, I am a creationist, but I'm just trying to get some facts for now, please no arguments or sarcastic comments, and please include any available sources. Thx

Answer 1

1. No.  Not exactly, and definitely not initially.  Most recent numbers I've seen are actually 92%.  The high numbers at 95-99% are early estimates that focused on coding sequences/gene sequences.  Coding sequences are extremely similar, with ~29% of genes being virtually identical (the differences being as great as within each species).  Junk DNA, which unsurprisingly is under weaker selection if any at all, is more different.

2. Yes.  This one of the basic things needed for constructing phyogenetic tree.  We are far more similar to chimpanzees and other primates than other mammals.  Modern day phylogenetic trees are based on genome/genetic data that we are discussing right now.

Answer 2

1. There has not been just one study, but several, and are based on different samples, but increasingly larger samples of the genome of the two species, not the entire genome (yet).   However, the samples have been getting larger and larger, and all seem to agree with the earlier methods.   The complete genome of the human was not sequenced until 2003, and for the chimp in 2005.

The most recent study I know of is based on 2,400 million base pairs (out of 3164.7 million bases in the total genome), which is about 75.8% of the genome.  

By the way, the specific way of computing differences can produce slightly different results ... which is why some sources will say 96% similarity (4% difference) while others will say 98% similarity (2% difference), but the point is that (a) that the similarity is huge, and (b) that the same method is used when comparing with other species.

2. Yes.  They do contrast this with comparisons with other genomes.    This is a key part of the whole picture of what this DNA similarity means.  It's not just that the human-chimp difference is only 1.68% ... but the human-gorilla difference is 2.33% ... and the human-orangutan difference is 5.63% ... etc.

(See the table here:

http://en.wikipedia.org/wiki/Human_evolu...

Here's a good visualization of how the DNA differences between three species of apes (humans, chimps, gibbons) and two species of elephants (indian and african elephants) reveal DNA similarities.

http://www.cs.ucr.edu/~eamonn/DNA/

Finally, I should add that David G is incorrect when he says that this is only mapping the genes, and not the rest of the genome (including the junk DNA).   This similarity absolutely does include similarities in the junk DNA ... which is another reason this is such *compelling* evidence in favor of evolution and common ancestry.  

Specifically, it refutes Teresa P's point completely.  The "common architect" argument holds only if the similarities and differences have architectural PURPOSE.  In other words, if they serve a specific common purpose that the two organisms have in common.   If two species share sequences that are letter-for-letter identical ... but are in areas of DNA that serve no function to *EITHER* species, then this cannot be explained as "common architecture."

Example:   If humans and chimps share the same sequence

"abccdefghijkl", but in gibbons we find the sequence

"abcdefghijkl", and IF this sequence is part of the junk DNA that does not affect any of the three species ... then the "common architect" explanation fails to explain why the "common architect" would put a useless double-c in the useless part of the genome of humans and chimps, but not in gibbons.  But the "common ancestor" explains it as an accidental duplication that got introduced after the branching from the gibbons, but before the branching of humans and chimps.

That these "markers" are everywhere ... in the junk DNA of *ALL* species ... and are absolutely consistent with a huge *branching* hierarchy (e.g. the markers don't contradict each other) ... tells a phenomenally clear story of common ancestry.

Shared *junk* DNA is NOT explained by "common architecture."

But shared junk DNA *IS* explained by common *ancestry*.  (The shared junk was inherited from a common ancestor.)

P.S. to Teresa P.   I am not an atheist, and am not setting out to "prove" that there is no creator (as I don't believe that).  My point is only that a thorough reading of the genetic evidence points to clear, unmistakeable markers of common ancestry between species.  That does not refute Creation (because God can use evolution as His mechanism), but it does refute Creationism (the belief that all species were created in their current state and have no ancestral ties to each other).  That's why your bio docs were not atheists, even though I *guarantee* they were supporters of evolution ... because evolution does NOT "disprove" God.

Answer 3

All living things have similarities in there genome. For instance bananas have 50% similar DNA to humans. Thats why we can consume them. Thats why monkeys can consume them. The DNA being similar means nothing. Even if chimps has 100 percent similarity, it means squat. Think of the Genome as a big library. The cell housing the DNA then picks and chooses (turns on and off) whatever books in the library it wants. So a chimps dna has different switched turned on and off than a human. So DNA is not the be all and end all of what makes a human or what makes a chimp.

And oh, to answer your original question, most of the DNA is classed as "junk" because nobody knows what it does exactly. So this "junk" DNA has not been mapped and checked for similarities.

The real issue is that you would expect all living things to fairly similar as far as genome mapping is concerned by necessity. IE we all need to eat other living things with similar DNA to replenish our own.

Answer 4

I am a creationist and have an MS in Biology.  I have done many electrophoretic studies on different species of animals.  Yes, they have done studies comparing many different types of animals.  Interesting point, our DNA is more similar to a rats than to a horses.  These similarities are called evolution by some.  I see them as signs that all the organisms had the same architect.  Historians look at building patterns and predict who built them, art critics look at brush strokes and determine authenticity of paintings.  My belief is that if we were all created by the same God, it is only natural that he would use the same pattern in his creations.  In graduate school, oddly enough, I never encountered a professor (all docs in bio) who was an atheist.  I did, however, meet several freshmen who thought they knew enough to deny the existence of a creator.