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.

Comments

Bogus

[inertia187]

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).

We've only fully mapped the human genome so far. I bet if we fully mapped the chimp genome, we'd see many many more entries in the diff log than we thought.

Re:Bogus

[Michael Woodhams]

According to my handy textbook*, orangutangs are about twice as diverged from us as chimpanzies. The numbers** here are the number of nucleotide substitutions per 100 sites (i.e. approximately % difference.)

Human-Chimp: 1.45
Human-Gorila: 1.51
Human-Orangutang: 2.98
Gorilla-Chimp: 1.57

Standard errors on these numbers are about 0.2, so the human/chimp/gorilla differences are not statistically significant. The evidence is growing that the human/chimp split is more recent than the gorilla split, but as far as I know this hasn't yet been determined beyond reasonable doubt.

The numbers in the article are only looking at DNA nucliotides in genes, which change much more slowly then the bulk of DNA which is 'junk'. This is because inside a gene, most mutations will be disadvantageous and selected against. The numbers I give above are from non-coding DNA.

Note that even within genes, not all nucleotide substitutions have any evolutionary effect. There are 4 nucleotides (think letters) which come in groups of 3 (codons, think words) giving 64 possible codons to code for 20 amino acids (plus a little punctuation) so most amino acids have several codons that code for them. Therefore even inside a gene, some nucleotide substitutions will be 'synonymous' - they will not change the protien generated from the gene.

For the purpose of saying "How different (functionally) are we from chimpanzees", it makes most sense to look at how different the proteins are - non-coding DNA and synonymous changes within coding DNA have no effect on phenotype (the critter that the DNA builds.)

For the purpose of timing evolutionary branchings, it makes most sense to look at non-coding DNA and synonymous substitutions. This is because the rate at which substitutions/mutations occur at these sites is much less variable than at coding sites. At coding sites, the rate is constrained by evolutionary pressures, and those pressures may not be the same on different lineages.

Anyway, the story looks like a big yawn to me - this isn't anything we haven't known about for years. There's probably lots of interesting stuff in the details, but not the '99.4%' number. Saying this means were in the same genus is pure sensationalism - the concept of genus is more fuzzy than species, and is fairly arbitrary. There is a fair argument that homo and pan are separate genii(?) only because of parochialism, but this data is not a strong reason to change it.

* I'm studying up for my new job in molecular phylogentics. It will be something of a challenge, given that my degrees are in physics and astronomy.

** Book is Molecular Evolution, Li, 1997. Data is from Li et al 1987.

Classification System Stinks

[Superfreaker]

Well, it may not be completely stinky, but it is close.

Our current system for categorizing the inhabitants of this is long outdated and is based largely on phsycal characteristics of the components on the creature, rather than the stuff it is actually made up of.

We find we've had to tweak this existing system to make new species fit. We've even had to add new kindoms! Many species bridge, these categories making them all the more harder to classify.

A better, more accurate, system needs to be devised based on current technologies that classify based on genetic code. The point of a classification system would be to allow us to draw similarities in creatures while studying them based on available data for ones in the same category. A genetic model would be very beneficial for this very reason.

IMHO.