When Fish First Breathed Air, by PBS Eons

Have you guys seen videos from PBS Eons? I’ve enjoyed their explainer videos. They’re my level. :slight_smile:

I thought this particular video did a good job with some topics that are common in discussions on the forum, like organs being coopted for other purposes as new needs arise.

What do you think? Does the presentation represent the science well?


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I’m not the scientist here at all, but I’ve occasionally watched the series just to learn more about what the current views of evolution are, since they are in a lay-friendly format and when a topic piques my interest.

But if you haven’t noticed, they do provide reference links to all the related papers in each video. There are about a dozen in that video’s description. (You have to scroll down quite a ways.) I haven’t watched this one yet.

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The presenter made mention of experts subscribing to the hypothesis that primitive lungs derived from exaptation of swim bladders, but this appears to be wrong because lungs were present long before swim bladders came along. In fact, it appears swim bladders evolved from primitive lungs in our fishy ancestors. In other words, modern swim bladders and modern lungs are descended from primitive lungs.

Actual paper (paywalled, but the above link nicely summarizes its findings):

Another somewhat related paper (also paywalled):


This error makes me more skeptical of the other claims in the video I couldn’t verify. However, its a fun and simple presentation with cool graphics and an alluring presenter, that really makes you appreciate your fishy ancestors for simply trying to breathe.

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Swim bladders would seem to be an actinopterygian invention, and there is a placoderm fossil showing preserved lungs. I would definitely like to see the primary literature that’s the source of the video’s claims that swim bladders came first. Consider also that the supposition that lungs originated in the neighborhood of Eusthenopteron is contradicted by the fact that modern Dipnoi have lungs too. Nice pictures, though. And the position of the spiracle is an interesting point I hadn’t been aware of.

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There are links in the video description on YouTube, so it might be there. However, I can’t use or identify the target link because they are all abridged.

I don’t know when this video was made, but if its recent I am left wondering why they would have made such significant errors.

Yes the graphics are great and even though there are errors, I guess I learned something about lung evolution because of them.

This is apparently also confirmed by two new studies in comparative genomics, illuminating the fish-to-tetrapod transition:

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The video appears to be from 2018. Could that explain the errors?

No. The last person I know of who claimed that lungs might have evolved from swim bladders was Charles Darwin. The phylogeny of fish has been well enough settled for at least 50 years, and the placoderm with lungs was discovered long ago too.

But now I see that the latter is controversial and may be untrue:

Still, there was plenty of evidence for lungs → swim bladders long before 2018, and I don’t know of anyone in the last hundred years (in the primary literature, that is) who proposed otherwise.

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