Do Higher Eukaryotes Smoke More Weed?

I need to vent . . .

I'm sick and tired of people referring to "higher" and "lower" eukaryotes. And, while I'm at it, I'm also sick of people mixing up "homology", "identity" and "similarity". This is nothing new; I've just reached a point where I need to write it down for the world to see.

First, the 'higher' eukaryotes thing. Measured how? Most people mean animals when they talk about 'higher' eukaryotes. Some are also referring to plants, I think. But I'm not sure, and that's the first problem: it's a meaningless term. Refer to clades and save us all some time and angst. Second, if both plants and animals are 'higher' eukaryotes, then it's a paraphyletic group -- they got high separately (see the eukaryote tree here). I guess the dutchie weren't being passed between the algae and the metazoans.

And, if you study biology, take some time to learn what homology means. Two sequences/structures/whatever are either homologous or they are not. There are no degrees of homology. You can't measure percent homology. Homology just means they share a common ancestor. If you want to say how divergent they've become since their common ancestor, then tell me what their percent identity is (if it's a DNA sequence). If you want to make a comparison based on function or some higher order analysis beyond simple sequence comparison, then you can refer to their similarity. But don't say that two sequences have low homology or high homology because you sound like a retard.

I have taken to asking stupid questions to people that misuse these terms. You could be next on the list, and you don't want that. Or do you?


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Trees are pretty tall as well. My guess for 'highest' eukaryote would be marine kelp, which I think can top 100m, but I'm happy to stand corrected on that...

I think dolphins and whales are the highest mammals. They were smart enough to get back in the water where we belong.

I'd say the highest eukaryote had to have been Dr. Timothy Leary--both before and after his remains were shot into space.

I see the dichotomy more commonly applied to vertebrates--fish & herps vs. birds & mammals--and find it equally annoying.

(yes I know "herps" is paraphyletic)

Higher and lower are problematic, as are primitive and advanced, largely because of a tendency to define those terms in relationship to a funny looking naked ape. Back when I took my bio degree (pre-PCR, never mind the whole genome thing) I believe I was encouraged to used the terms "derived" and "conserved" traits when thinking about taxonomic relationships. The idea was to get away from hierarchical thinking (less tree or ladder and more bush) when talking about evolution.

By justawriter (not verified) on 18 Oct 2006 #permalink

Some journals have rules about using the words "homology" and "similarity" correctly. For example, in the instructions to authors for the Jounral of Molecular Evolution it says,

Homology: The term should not be used in the sense of structural similarity but only in its biological sense of derivation of structures from a common ancestral structure.

Unfortunately, the editors do not enforce the journal policy.

Many Ph.D. candidates in our department have been forced to revise their theses because they were unfortunate enough to have me on their committee. If they can't even understand the meaning of a simple word like "homology" why are we giving them an advanced degree?

(Yes, I know, it's the fault of their supervisor and not the student. Problem is, I can't flunk the supervisor!)

By Larry Moran (not verified) on 18 Oct 2006 #permalink

He finalized the project when he input the last data.

Finalized is some manager's idea that since computer guys talked about initialization that this must also be a word. input is a noun, not a verb. Use the verb entered. Data is plural. Datum is singular.

Technical language is constantly abused by the uneducated masses into meaninglessness. The language becomes a neobastardification.

I've largely given up, though. This is English we're talking about. The average American child of 10 has a 10,000 word vocabulary, and knows some 10,000 rules of grammar. Proving that there is an exception to every rule. Even this one.