Remnant Feature in Human Embryos

The BBC posted an interesting article yesterday about [lizard-like’ muscles present in developing human foetuses](Babies in the womb have lizard-like hand muscles https://www.bbc.co.uk/news/health-49876827). Features which vanish before the baby is full developed. The appearance and disappearance of features in utero is call recapitulation. Personally, I always found things like this one of the most compelling evidences for evolution.

I wonder what others make of it.

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Fascinating. Way back in comparative anatomy, the common saying was “ontology recapitulates phylogeny.” That idea has largely been superseded by evo-devo as I have learned here on the forum, but this example is one that illustrates modern evo-devo concepts well, I think.



Of course, this has led to the evo-devo song: https://m.youtube.com/watch?v=ydqReeTV_vk

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It hasn’t been called that for a long time. Recapitulation theory, most commonly associated with Haeckel, was discredited many decades ago.

The observations that spawned recapitulation theory do include–but are not limited to–vestigial structures. I think that its proponents were just as impressed by the morphological (shape-related) stages through which many animal embryos pass during development. I don’t know whether they were also impressed by atavisms, which are also very well explained by common descent.

Evo-devo, as @jpm mentioned, has moved far beyond recapitulation.

I wonder if “recapitulation” isn’t still okay in a descriptive sense. Not that organisms literally take on the form of earlier transitional forms, but what we see might approximate similar developmental stages in ancestral forms. I guess the naive assumption might be that everything would be the same in a current organism and an earlier transitional form until some new twist toward the completion of the birth-ready form. But the key changes might actually happen earlier or later in the developmental process, couldn’t they?

@jpm I never get tired of hearing that song and watching the video.

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Developmental biologists don’t use the term in this context, for good reason IMO. You are right that it’s a fine English word descriptively, but in the context of evolution and development, it’s freighted with overstatement and error. I think the history matters in this case.

Sure. That’s basic evo-devo.

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Shoot! Vestigial structures! That was the term I was grasping for - I thought recapitulation didn’t sound right. Thank you for the helpful course correction @sfmatheson. I’ll be more careful to double check before I post next time. :man_facepalming:t2:

Still the evidence for structures and features that existed in ancestors past that vanish Or become something else as the embryo is develops is fascinating. And I believe is a compelling evidence for evolution. Personally, I don’t know how else to make sense of them.

I’d be interested in hearing what any YECs/OECs out there make of it.

Thanks also to @jpm for the info on evo-devo (my autocorrect hates that word!!!). I’ll take a look at the info.

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