Remnant Feature in Human Embryos

[LM77 (Liam Maguire)]

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 Babies in the womb have lizard-like hand muscles - BBC News). 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.

[jpm (Phil McCurdy)]

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 That idea has largely been superseded by evo-devo as I have learned here on the forum, but this example is one that illustrates modern evo-devo concepts well, I think.

Recapitulation theory

Evolutionary developmental biology

Of course, this has led to the evo-devo song: Evo-Devo (Despacito Biology Parody) | A Capella Science - YouTube

[sfmatheson]

@LM77

The appearance and disappearance of features in utero is call recapitulation.

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.

[MarkD (A Whateverist, not a Christian)]

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.

[sfmatheson]

@MarkD

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.

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.

@MarkD

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?

Sure. That’s basic evo-devo.

[LM77 (Liam Maguire)]

@sfmatheson

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.

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.

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.