Slashdot Mirror
Chimps Belong in Human Genus?
Bradley Chapman writes "I found this interesting story from Discovery News about our ties with chimpanzees. Excerpts: 'Chimpanzees share 99.4 percent of functionally important DNA with humans and belong in our genus, Homo, according to a recent genetic study.
Scientists analyzed 97 human genes, along with comparable sequences from chimps, gorillas, orangutans and Old World monkeys (a group that includes baboons and macaques). The researchers then took the DNA data and estimated genetic evolution over time. They determined that humans and chimps shared a common ancestor between 4 and 7 million years ago. That ancestor diverged from gorillas 6 to 7 million years ago.'" Genus is the next step up from species, if you recall your taxonomy. Humans are the only living species in genus homo, currently.
For what it is worth, the raw similarity in the genome sequence doesn't need to indicate the same degree of similarity. Transcription is quite complex (much of it we still don't understand) and it is possible that small differences in regulatory regions can cause completely different parts of the sequence to be expressed.
Google for phylogeny, or just check out this page for a relatively good introduction. Comparative geneticists use sequence comparisons between species to determine relative evolutionary separation, much like the subject of the article. We haven't gotten rid of the kingdom-phylum-order-class-family-genus-species thing yet, but we're working on it.
Great spirits have always encountered violent opposition from mediocre minds. Albert Einstein
"The human genome is estimated to have as few as 30-45,000 functional genes" - Imperial College London (http://www.ic.ac.uk/P3509.htm)
Where did you get your "couple quadzillion" number from?
If you read this, you'll see that the analysis is based on 97 'critical' genes where a difference in a single base will produce a change in the amino acid coded for, and hence a change in the protein.
If the 'junk' DNA is included, there is more likelihood of variation between humans and chimps, but there is a corresponding rise in the variability within the human population which tends to lessen the overall significance of the inter-species variation.
Other than the fact that evolution would tend to favour the stability of these 97 'critical' genes, I see no problem with this analysis, but think that putting humans and chimps in the same genus is pushing matters slightly.
oh brave new world, that has such people in it!
Wolves are not genetically identical to dogs, any more than beagles are genetically identical to rotweilers: the consistent phenotypic differences between dog breeds, and between dogs and wolves, are genetically determined.
If being genetically identical were the key, each human (or pair of twins) would be a species unto himself.
But what people mean by species is usually more determined by whether the animals interbreed and produce fertile offspring (this gets fuzzy with plants and is more or less irrelevant to bacteria, but still...).
Dogs and wolves are close enough to interbreed, successfully and often, and a lot of people would class dogs as a subspecies of wolf (Canis lupus latrans).
But classification by genus and higher levels is fairly arbitrary, based mostly on what people see as significant differences and similarities (e.g. people are different from apes, cats all kind of look alike). The only important thing is that the basic nesting is right, so that if species A and B have a common ancestor, and C and D are descended from B, then if A and C are in one class, B and D are also in that class.
It might be more rational to have a system that took each branching into account, but we don't have enough information for that, and it would be inconvenient to deal with.
To sum up: the argument that no one calls a wolf a dog is incorrect, but there's still no point in calling a chimp a Homo.
So far
total human reads: 23 million
total chimp reads (Pan troglodytes): over 12 million
having worked on annotation of a few of the chimp BAC clones, I can assure you the two species range from about 97% to over 99.9% similar at the DNA sequence level.