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Just to add: if anyone is interested in learning more about the sudden appearance of extremely varied life, this event is called the “Cambrian explosion” and makes for some very interesting reading.

Cambrian Explosion is a bit of a misnomer because it leads people to think it was unique with respect to evolutionary processes. There is a push to call it the Cambrian Radiation [0]. Throughout complex life's time on Earth there have been multiple periods of rapid evolutionary development similar to the Cambrian. A blurb about the Cambrian Radiation appears in my coffee table picture book [1].

[0]: https://impacts.to/bibliography.pdf#page=41

[1]: https://impacts.to/downloads/lowres/impacts.pdf#page=15

"Radiation" sounds more unique than "explosion" to me (not an evolutionary biologist). It sounds like it means there was some unusual atomic radiation causing mutations at that time, so I think it will lead to more misunderstanding by laypeople rather than less. Why did they decide not to have multiple "explosions"?

Your book looks really interesting!

"Radiation" is meant to suggest that the evolution advanced in many very different directions, like the rays that diverge from a point.

Such "radiations" have happened every time when there was little competition either because a new place or environment was invaded or because a catastrophe had eliminated the former incumbents.

The result of evolution "radiations" was that some group of animals that previously had been more or less uniform because they were adapted to a certain niche, after the "radiation" event became diversified in a large number of groups adapted to very different conditions of life and having much less resemblance between themselves than before.

Yes I understand what it means, but the word "radiation" has other much more well-known meanings, one of which directly connects to having more mutations than usual, so it's bound to be misunderstood.

You are right about the risk of misunderstanding the word "radiation".

However, the same risk applies to "explosion".

It is probably better to not use metaphors like "radiation" or "explosion", but to just say something like "diversification event".

However, "radiation" already has a long history of being used in the biological literature with this particular meaning, of divergent evolution, so for those familiar with the jargon, it seems an appropriate choice, even if it might not be the best word to use in something intended for the general public.

The "radiation" events are not events when the rate of mutations was higher (even if it is likely that the mutation rate during Cambrian was a little higher than today, due to higher ambient radioactivity because less of the primordial radioactive nuclides had already decayed by then).

The "radiation" events were events where a much larger proportion of mutants survived enough to have descendants, because of less competition that would have otherwise eliminated them.

This allowed a chain of neutral or bad mutations to lead eventually to improved organisms for certain conditions of life, while in the times of high competition it would have been impossible to escape local optima.

So while the rate of "raw" mutations was about the same as in other times, the rate of successful mutations, that persisted in the DNA of the descendants, was higher.

Maybe Cambrian diversification/surge would be a more neutral name?

This book looks fantastic - just perfect to capture the interest of the layman. If it ever get translated to my language it is going on my coffee table as well.

Did you coin the term Cambrian Radiation? Though I agree that the term Cambrian Explosion may mislead, I fear that the term Cambrian Radiation might confuse. If a new term is to be coined, wouldn't Cambrian Diversification be an obvious choice?

I fear that the term Cambrian Radiation might confuse

I have surmised the OP actually meant Cambrian Radiance, not radiation. Autocomplete might have been complicit.

Radiance sounds so much better than radiation

Search for "radiation" and "radiance" in the book's bibliography:

https://impacts.to/bibliography.pdf

A printed version costs about $150 to produce, which includes $15 that goes to the illustrators. Translating to other languages would be a technical challenge. I didn't coin the term Cambrian Radiation; you can find the phrase referenced by biologists many times throughout the book's bibliography:

https://impacts.to/bibliography.pdf

I see, thank you for the details.

> There's even the suggestion that there are creatures that can't really be classified into plant or animal - it's not clear what they are at all.

No plant or animal, but alive. How strange, rare and exotic ... like a mushroom?

(Mushrooms are not a plant nor animal either, but if you look close enough, mushrooms are indeed strange and exotic, though)

You are correct. I believe there are five kingdoms of living things, and mushrooms belong to fungi.

https://www.iberdrola.com/sustainability/biology-kingdoms-li...

https://www.iberdrola.com/wcorp/gc/prod/en_US/comunicacion/r...

The number of domains/kingdoms/empires/superkingdoms of living things is actually much more of a matter of debate amongst taxonomists than people realize.

Taking our classification schemes as a fact about biology is confusing the map for the territory.

But you are correct that mushrooms (which is the fruiting body of some types of fungi) are separate from plants (and actually more closely related to animals. They're basically animals that digest things externally instead of having a stomach to digest things internally)

We digest externally too. We just carry the outside around with us.

This shouldn't have been downvoted; external digestion, usually known as "cooking", is one of the most important features of human biology, explaining why our intestines are so short.

An animal’s gut is also arguably “external”, in the sense that the gastrointestinal tract means an animal is a topological torus, and the contents of the gut are also “outside” of the body. It’s an open question how the closed digestive tract evolved, but it presumably came from a digestive surface of some sort folding over on itself, since it must have evolved in creatures that were previously able to digest. The same general phenomenon presumably produced lungs by cavitating a gas-exchange surface to increase surface area.

If you have further reading material on these two developments, I'd be thrilled to go over them. The subject is fascinating, but layman subject matter is scarce and I already have a profession.

Well, a digestive surface is necessarily external in that sense, since the only things you want to digest originate outside the body. The options are that you have a digestive surface that is open to the world, or that you have one which is protected within your interior, but nevertheless topologically external.

Or, I guess, that you have a topologically external surface which does nothing but create vacuoles around food, which then get transmitted to a topologically internal digestive surface. (Similar mechanisms do exist for other purposes; one thing that may happen to a splinter embedded in your finger is that the body applies a protective coating to the splinter and then expels it.)

Starfish seem like an interesting case here, in that they have an ordinary internal stomach which they extrude, when they're eating, for the purpose of external digestion.

Short intestines are a characteristic typical of predators.

Our ancestors probably started as insectivores / frugivores / egg eaters

I agree that cooking is a form of digestion, but that is not what I was thinking when I made my comment. We are walking tubes. The cavity inside of the tube is still external to the tube itself.

This is a video that partially explains the concept.

https://youtu.be/vuIlsN32WaE

I wouldn’t call fungi exotic.

There are fungal spores pretty much everywhere, healthy animals are just particularly good at keeping they’re active forms at bay.

hutzlibu was ironic.

That you didn’t see this, make me think that some cultures have more use of irony than others. I can imaging that in a potpourri of cultures like the USA irony can often be misunderstood and therefore is less used than in other countries.

Wow, that’s a lot of extrapolation from one comment.

First of all, TheSpiceIsLife is Tasmanian according to their bio.

Second, even if they were American to then assume that all Americans can’t pick up on irony or sarcasm because one person on the internet missed an instance of it is quite the stretch.

Well, I said, if you look close enough, you might find them to be much more alien and exotic, than one would expect.

Yeah sorry I misreads the context of your comment.

The kingdoms Protozoa and Chromista include some former algae that have also motile 'spermatozoan like' forms in its lifecycle. The were plants before, but in some parts of this lifecycle they act like microscopic animals.

There was recently a discussion here on HN about the billion years of lost sediments on earth, and one article mentioned that that the crushing of that sediments into the sea lead to much more minerals in the sea and to the Cambrian explosion.

>a very small number of basic types of animal - (perhaps only 5?)

Anyone know what the ~5 types are?

> Five types of animals

I think that he could be confusing animals with the five groups of vertebrates. IMAO, Is common in English to use animals mostly for big animals with bones and critters or bugs or "somethingsomething-fish" for everything else.

If we need to choose just five, among the really, really successful types of animals (in a very broad sense) we have Mollusca, Artropoda, Cnidaria, Chordata and... lets see, I would dobt between Platyhelminths because most vertebrates are hosts of several of them, or maybe Nematoda because they are hugely influential and everywhere in the soil in large amounts.

But we have also a lot of other groups: Annelida, Porifera, Echinodermata, Brachyopoda, Bryozoa, Priapulida etc... Definitely more than five big types of animals.

Thanks!

> There's even the suggestion that there are creatures that can't really be classified into plant or animal - it's not clear what they are at all.

Could you expand on that at all? It sounds really fascinating.

All life of course at this time is in the ocean.

There's things that look like ferns, and are attached to the sea floor. But they lived at such a depth that the sunlight would not have been able to reach them so they could not have been plants.

https://en.wikipedia.org/wiki/Charnia

"The living organism grew on the sea floor and is believed to have fed on nutrients in the water. Despite Charnia's fern-like appearance, it is not a photosynthetic plant or alga because the nature of the fossilbeds where specimens have been found implies that it originally lived in deep water, well below the photic zone where photosynthesis can occur. "

Fascinating, thanks for sharing!

I think science is interesting enough in its own right that you don't need to oversell it. It is not a 'massive creature', but it's fascinating nonetheless when explained in context and without the clickbaity headline.

Massive for its time. Average creature being a pinky finger (why didn't they just say a number), so about 5 cm. Half meter is 10x that. Something 10x bigger than me is not a giant, it's a titan.

Moose make a great learning experience to demonstrate scale. They're goddamn huge. Nobody expects moose hugeness.

Compared to the average size of creatures of the time, then, this thing would be like the biggest ever moose to us.