I know "Krebs Cycle", "junk DNA", and other cool phrases
February 25, 2008 10:09 PM   Subscribe

Apparently, ontogeny recapitulates phylogeny! Which I can only assume means something!

I've searched the AskMeta archives, and seen the phrase "ontogeny recapitulates phylogeny" used about ten times, but none of them explains what the phrase means. Could someone give me an explanation in very, very small words? My knowledge of biological processes is limited to a) what I can remember from 1986 in AP Bio, and b) what I experience first-hand when I eat too much chili.
posted by tzikeh to Science & Nature (16 answers total) 5 users marked this as a favorite
It's the incorrect belief that the developmental stages fetuses go through are like a mini-version of how their species evolved. So a human goes through a single-celled organism phase, and a phase when it looks like a little fish, and a phase when it looks like an adorable monkey, and so forth. Or at least that's what I remember from AP Bio.

http://en.wikipedia.org/wiki/Recapitulation_theory for more.
posted by crinklebat at 10:16 PM on February 25, 2008

This might help.

It basically means that as a organism grows from conception, it somehow retraces the evolutionary steps from its ancestors. The theory was formed from examination of mammalian fetuses and noting how they look more like fish or lizards. No serious biologist believes this anymore, however.
posted by demiurge at 10:17 PM on February 25, 2008 [1 favorite]

phylogeny ~= progression of evolution of an organism
ontogeny ~= progression of development of an organism from conception

The stages an organism progresses through as it develops, can be mapped onto the stages of evolution.

(I guess checking wikipedia might make sense -- this is how I understand it and may be wrong)
posted by anadem at 10:17 PM on February 25, 2008

It's basically a clever way of saying that the collected evolution of various organisms can have a similar basis or grounding in their early embryonic states, that's all.

If you look at developing embryos from different organisms, from humans to frogs etc., you'll notice that we all look pretty similar from conception on up to certain developmental "checkpoints", a timeline where species start to distinguish themselves in appearance and function.

The further away two species are (their "phylogeny" or "phylogenetic distance"), the earlier the point at which embryos start to differentiate ("ontogeny").
posted by Blazecock Pileon at 10:18 PM on February 25, 2008

Well explained above. It was the going theory for a while in the late 1800s - early 1900s. No longer accepted as true. Though cool to think about; you can see why people were attracted to it.
posted by LobsterMitten at 10:24 PM on February 25, 2008

phylogeny ~= progression of evolution of an organism
ontogeny ~= progression of development of an organism from conception

might be clearer to say
phylogeny = development of the species over time, how life-forms evolved from single-celled to multi-celled to wormy to fish and so on.
ontogeny = development of a given individual over time, how the fertilized human egg divides into a multi-celled thing, then a wormy thing, then a fish-like thing, and so on, as it develops in utero.

So, the development of an individual organism retraces the steps taken by its species during evolution.
posted by LobsterMitten at 10:28 PM on February 25, 2008

Just so I don't look like the total idiot I may be, I did, in fact, check Wikipedia before coming here. It didn't do a particularly good job of breaking it all down into words that are for people who know *nothing* about biology. Even recapitulates - to me, that means "summarize at the end". So I'm still not quite getting the concept. The idea (even if it's wrong; that's not my question) is that the development of a foetus is a "summary" of the evolution of man?
posted by tzikeh at 10:51 PM on February 25, 2008

It's a concise repetition of the evolution of man, yeah, that's the idea.
posted by LobsterMitten at 11:06 PM on February 25, 2008

In this context, the word "recapitulates" might better be read as "replays". So the phrase means "fetal development replays evolutionary development" -- which, it is now known, is not correct.

Your meaning is related, in part because you're not defining it correctly. The recapitulation at the end of something is a rapid replay in brief of what came before. That's what they thought was going on in biology: a rapid replay during fetal development of the long evolutionary path by which that species developed.
posted by Class Goat at 11:06 PM on February 25, 2008

I think that's a reasonable shorthand summary of the concept.

I've always thought this saying would be great cross-stitched on a pillow!
posted by Enroute at 11:07 PM on February 25, 2008

A better thing to say: Replace "recapitulates" with "repeats".
Organism-development repeats species-development.
posted by LobsterMitten at 11:09 PM on February 25, 2008

I think you've got it, but here's how I understand it:

Imagine a time-lapse movie of the development of man, in which man starts out as a tadpole-looking thing and ends up as the man of today. (Phylogeny)

Now imagine a time-lapse movie of embryonic/fetal development. According to the theory, they should look pretty much the same. (Ontogeny)

The summary definition works pretty well, actually. It's sort of like fetal development acting as a Cliffs Notes version of evolutionary development.
posted by stefanie at 11:27 PM on February 25, 2008

I should point out that Stephen Jay Gould wrote a book called Ontogeny and Phylogeny that discusses these concepts.
posted by grouse at 11:41 PM on February 25, 2008

I'll recommend you go and read P.Z. Myers on "Wells and Haeckel's Embryos", which gives good background to the ontogeny - phylogeny claim. The piece is more proximally about Wells's silly Intelligent Design book, by the way, but Myers discusses Haeckel's notion at some great length.
posted by Emperor SnooKloze at 3:28 AM on February 26, 2008

Myers' article is really interesting, and worth a read. This was new to me, so I'll try a short-form digest to lock it into my head, and potentially reach someone who doesn't have time for the whole thing.

Per Myers, you can't really tell what an organism used to look like by the stages it goes through during development, because changes could have happened anywhere along the way. The fact that human embryos look like fish is not a guarantee that our adult ancestors looked like fish.

The fact, however, that almost all embryos look very similar, and only differentiate strongly near the end of the process, is very powerful evidence of evolution. The simple explanation, that you can 'see' the evolution by the body forms, is wrong. But the slightly more complex explanation, that chicken embryos and human embryos look so similar because we share the same origins, appears to be correct. The more closely related we are genetically to a creature, the more closely our embryo development corresponds to that creature.

The outer similarities of embryos to adult versions of other animals are a mask, a distraction. What they look like doesn't matter. What DOES matter is that they all look like each other, from fish to chickens to people.
posted by Malor at 5:46 AM on February 26, 2008 [1 favorite]

...almost all embryos look very similar...

Almost all vertebrate embryos look very similar.
posted by Class Goat at 3:02 PM on February 26, 2008

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