Ontogeny recapitulates phylogeny

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flycd05

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There's a question in destroyer that asks for the meaning of this phrase. However, the way the answers are worded are really confusing.

I'm pretty sure I know what the phrase means - basically that whatever embryological developments one organism goes through, the entire lineage goes through as well right? The example in shaum's is confusing as well - they say that gill slits are present in all mammals during development which basically implies that all mammals will go through a "fish" stage at some point. Can someone clarify this and/or give another example displaying this phrase!

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There's a question in destroyer that asks for the meaning of this phrase. However, the way the answers are worded are really confusing.

I'm pretty sure I know what the phrase means - basically that whatever embryological developments one organism goes through, the entire lineage goes through as well right? The example in shaum's is confusing as well - they say that gill slits are present in all mammals during development which basically implies that all mammals will go through a "fish" stage at some point. Can someone clarify this and/or give another example displaying this phrase!

I haven't gotten to that question YET...but I took both comparative anatomy and evolution last semester soooo hopefully I can try to help. I think this was a statement put forth by Haekel and basically is means that embryonic development (=ontogeny) follows a path similar to phylogeny (you know, like that good old phylogenetic tree where at the root of the tree, there is one sole common ancestor to anything that ever lived). Picture a phylogenetic tree and also picture a newly formed embryo. Now picture three creatures on the phylogenetic tree, say a frog, a chicken, and a human (assuming the frog is more primitive than a chicken, and a chicken more primitive than a human). As they develop embryonically, they all LOOK exactly the SAME at first. This is because they share a common ancestor at some point in time. Now as they each develop, they start looking more and more different. This is like ancestry where they all have some common features, but as each evolved, they accumulated special features to set them apart. Think of the embryos now accumulating these differences in a matter of days or weeks just like animals accumulated differences through out evolutionary history. Mid-way through development, the frog will look much more different than the chicken or human. Since at the later stages of development the chicken and human embryos look more similar to each other than to the frog, it could be thought that the chicken and human share a more recent common ancestor and are thus thought to be more closely related.

Main idea: More closely related creatures resemble each other more than less closely related creatures towards the end of development.

Sorry if I confused you more than before ;)
 
Yeah, that question confused in destroyer confused me a lot too. "Ontogeny recapitulates phylogeny" is what Optimum Smiles said---its the theory that you can tell we evolved from, like, fish because our embryos at some point have gills. Its saying that the embryo goes through phases that are like the evolutionary history-- like it'll look like a fish, then an amphibian, then a reptile, then a mammal, and then a human being.

But the thing is is now thought to be false in regards to evolution. They dont think the embryos go through the different phylogenies-- its just that since the species are somewhat closely related, they have similar embryonic developments.

So the question was asking what the theory means, but you need to know that its not true. I didnt like the question lol
 
In short, evolutionary relationships are "shown" by early development.
 

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