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

[Black Parrot]

> 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.

...and many more similarities as well. Welcome to the concept of "percent".

However, the real reason for the bogosity of the claim is that clades aren't defined by thresholds in DNA differences. The tree of common descent is there, but it's somewhat arbitrary how far up from a leaf you go before you reach a node that you call "species", "genus", etc. They are merely labels of convenience, and if we suddenly do or don't find it convenient to put the chimps in the genus Homo it doesn't really tell us anything we didn't already know about the relationships in that branch of the tree. (I have a physical anthropology textbook published ten years ago that already mapped out this branch of the tree according to our current understanding of it, then already based on DNA comparisons as well.)

The real news from this is that by focusing on "functionally important" genes we now know that our "functionally important similarity" is 99.4% rather than the 97.whatever% that we previously got when looking at genes in general.

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.

Re: Bogus

[the gnat]

They are merely labels of convenience

Incidentally, this is one reason why creationist blather about speciation is a load of bull - there isn't really a strict definition for speciation on the molecular level. It's a series of events that are well documented, but there isn't one point where you suddenly get a new species. Creationists talk about speciation as if there's a sudden "promotion" or massive change that has to occur, but that really has no basis in reality. Speciation is simply the sum of reproductive isolation and mutation/genetic drift.

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.

Re:Classification System Stinks

[anzha]

There's another problem with this though if you want to go strictly genetics for your classification, paleontology.

The vast majority of work done by paleontologists simply cannot use genetics. They are almost completely stuck using comparative physical characteristics. I'm sure that they'll get some things wrong, as far as relations, but like I said, they're mildly stuck.

If you can come up with a unified classification system that satisifies both the paleontology and the genetics crowds, then you might just have more than a few papers and a PhD thesis there...;)

Antropomorphic principle

[Alomex]

The Antropomorphic principle is the name given by a tendency by us humans to believe that our situation is unique. It goes from believing in our divine origin, to the earth is the centre of the universe (Ptolomeic) to the sun is the centre of the universe (Copernicus), to the current incantation of the big bang (Gamow) with an ever expanding universe.

Placing humans in their own genus seems to fit right along those lines. We are unique, and no other animal deserves to be even close to us...

Someone had to say it...

[ConceptJunkie]

Keep your filthy hands off my genus, you damn dirty chimps.

I'm sure the creationists will pitch a fit if chimps are reclassified. I wonder if there would be any legal ramifications regarding the rights of chimps compared to other animals.

Re:But isn't the real test...

[sbeitzel]

Nope. That's only for species. Two critters are said to be in the same species if they can breed and have fertile offspring.

Take this with a handful of salt

[dusanv]

I think a good parallel would be programming. Say you have a 4000000000 line program (I think someone estimated that this is what the DNA translates to in terms of code but it is irrelevant). I can go in and change 100 lines and make that program not behave anything like the original. On the other hand you can change a half of it without making any substantial difference in the final result. The sheer amount of identical code is a good hint but by no means an accurate measurement of how closely related to chimps we are.

oh? just scientists?

[jpellino]

I got news for you... not only does the scientific community have those ideas about how unique and exceptional humans are ("how" unique?), so does
the literary community,
the artistic community,
the philosophical community,
the musical community,
the educational community,
the list goes on...
You shall know them by their works.

Re:Dumb

[buffer-overflowed]

I'd love for google to include scientific journals, but they all cost money, so we're forced to rely on the mainstream media for info (with all that entails).

Re:It's about time...

[shaper]

It's amazing to me that this comment was modded "Insightful". Chimps have had 4-7 million years since we split from a common ancestor (according to the article) and they're still swinging in trees. Humans are reaching for the stars.

It should be obvious to any cretin that there is a definite qualitative difference between human and chimp, indeed between human and all of (observable) nature. And that supposedly insignificant quality makes all the difference. The fact that we cannot (yet) measure its true magnitude in scientific terms does not make it any less ridiculously obvious. No human is just another monkey. Not even you.

As others have noted...

[jd]

It's time to re-write our classification system, anyway. Its origins are based in the dark-ages, where monks and scribes would describe species by how they looked, and grouped them accordingly.

Since then, other systems have evolved, and have been tagged on. In consequence, the current "system" is really a complete mish-mash of differing systems, with no real agreement on what system applies under what circumstance.

To those who advocate DNA-based classification, I'd argue that that only works on still-living species. If we don't have the DNA, we can't do that. So, we'd end up using some other system for those, anyway, which means we'd still be using a hybrid.

The argument that chimps belong to the "homo" group seems valid enough. We're not talking about direct ancestors, but about a common ancestor who is already established as a part of the "homo" group. (Percent then becomes irrelevent. Once you can establish that common ancestor, and establish that said ancestor is already classed as being in the "homo" genus, the rest becomes moot.)

The only rational argument I can see against it is if it can be established that the chimp branch has diverged in some critical way that, even though the divergence is small, would still place it in a different genus. You'd probably want to alter the genus to the verb, rather than the noun, in this case, to show the relationship while acknowledging the difference.