Question

[james_davis_nicoll]

Could we duplicate this effect with mutagenic pollution or a sufficiently dirty nuclear war?

Comments

[mishalak]

Well... Perhaps we will discover this in a limited way if we keep building nuclear power plants that blow up.

[tandw.livejournal.com]

Their method of testing seems flawed to me. Maybe I'm missing something, but how does one produce whatever anomalous isotopes they propose to look for from gamma ray flux? I was under the impression that it took neutrons to do that. That's aside from the question of whether the Cambrian Explosion is an actual thing or an artifact of preservation probability, which AIUI is still something of an open question.

[fridgepunk.livejournal.com]

induced fission - above a barrier energy level, a gamma ray will knock neutrons clean off an atom, like WIZZ! POW!

[tandw.livejournal.com]

OK, that makes sense. I'm still not sure that the apparent rapid increase in biodiversity is a thing that needs explaining, though.

[(Anonymous)]

A lot of argument about this, but close inspection of the immediately-preceding stages of the Cambrian indicate that there was already quite a bit of diversity, it's just that the faunae didn't fossilize well. The Cambrian Explosion itself extended over 20 Myr, as I recall, which is a fairly slow-motion sort of explosion.

[(Anonymous)]

The duration of a GRB event is measured in years (if not less); the duration of the Cambrian Explosion is measured in tens of millions of years. Their model needs a process as to how the aftereffects of a GRB continue operating for tens of millions of years.

Their model also has to account for the evidence of a preceding lag phase to the Cambrian Explosion.

The claim that the Cambrian Explosion differs from other adaptive radiations in not being preceded by a mass extinction is questionable - it has been suggested that extinctions associated with the Snowball Earth phase of the late Precambrian lit the fuse for the Cambrian Explosion.

[tandw.livejournal.com]

From my brief readup on GRB events, the bursts themselves are generally on the order of seconds or less. There's some speculation that a spike in C-14 and Be-10 dating to the late 8th century CE was caused by a burst, but I'm not sure how long the spike lasted.

[neowolf2.livejournal.com]

The gamma rays arrive in seconds to hours, but a GRB source emits those gammas from a jet of relativistic plasma. The particles in that jet, if the source were in our galaxy, would arrive at Earth over a much longer period, since they spiral around magnetic field lines and do not travel in straight lines.

[laetitia-apis.livejournal.com]

Yup. I see something like that every day, when an impossible puzzle suddenly falls apart, or something barely visible suddenly multiplies all over the garden. Each increase in variety made more increases possible, like water leaking through an ice dam.

[montedavis.livejournal.com]

Could have been something analogous to the homeobox "chunking" of gene regulation, or better cell-surface receptors for the kind of epigenetic signals Lewis Wolpert used to work on. Either would have enabled both larger size and more differentiated tissues and organs.

[keithmm.livejournal.com]

Still a lot of debate. I tend toward the threshold theory: you can find hints or outright examples of the things that showed up in the Cambrian from Precambrian fossils, some of them for a very, very long time (there's spiny fossils that would seem to indicate defense against predation at a billion years old). Then, when you reach some level of biological sophistication, all hell breaks loose.

The main problem is that the known Cambian biota are only from a handful (literally four or five) of lagerstätten, all preserving relatively calm shallow-water environments. There's not a whole lot of evidence about what else was going on in the oceans or tidal zones.

[neowolf2.livejournal.com]

Photoneutrons aren't just from fission. One effect is from the "Giant Resonance", where all the protons in the nucleus oscillate vs. all the neutrons. This is around 20 MeV in many nuclei, I think. The energy gets thermalized and then some neutrons evaporate (the binding energy of a neutron in a nucleus is typically around 8 MeV).

Some neutrons have much lower binding energy, with beryllium and deuterium being notable examples among the stable isotopes.

BTW, I suspect the radiation from the charged particles in the GRB progenitor's jet would induce much more radioactivity than the gamma rays themselves.

The whole idea of "lots of mutations => faster evolution" strikes me as utter crap, btw, particularly from an impulsive source of mutations.

[bruce munro (from livejournal.com)]

Indeed. Sounds like something from 1940s science fiction, not serious biology.

[montedavis.livejournal.com]

Well,"serious geology" spent a century weaning itself from catastrophism to Lyellian gradualism -- then had to strain to accommodate Bretz's Lake Missoula flood, Deccan Traps and other megavolcanic episodes, dried-up Mediterranean and Black Seas, etc.

Yes, SF (and some biologists) got fast and loose with big/coordinated mutations for a while there. That doesn't mean there aren't some de facto step functions hidden in the layers upon layers of gene regulation and epigenesis.

[tandw.livejournal.com]

Yes, SF (and some biologists) got fast and loose with big/coordinated mutations for a while there.

*cough* Darwin's Radio *cough*

Not to mention the little aside in Starship Troopers about how the inhabitants of the R&R world, reproductively relatively isolated from the rest of humanity, might have to seed the environment with mutagens to avoid falling behind in the pace of evolution.

[scott-sanford.livejournal.com]

We may be dubious about calling women who live near a recreation area for young military men 'reproductively isolated'...but that's not the story RAH was telling.

[tandw.livejournal.com]

Now you made me go look it up; it was something that I specifically remembered RAH alluding to, but it had been a while since I read it. From "Starship Troopers," p. 124 of the Berkley paperback edition (January, 1983 printing):

But the descendants of those colonists won't evolve. Not much, anyhow. This chap told me that they could improve a little through mutation from other causes, from new blood added by immigration, and from natural selection among the gene patterns they already own--but that is all very minor compared with the evolutionary rate on Terra and on any usual planet.

The fact that "new blood added by immigration" is a small effect compared to native mutations suggests a couple of things: 1) the planet is relatively reproductively isolated, and 2) Heinlein's biology was dodgy at best.

[scott-sanford.livejournal.com]

I remember the passage too. Apparently exogamous relationships were hard for some reason, or maybe RAH just didn't think it through - certainly interstellar travel didn't seem all that hard in that setting.

[neowolf2.livejournal.com]

If more mutations drives evolution, there's a simple way to get more: have a larger population. More creatures means more opportunities for mutated offspring. If an advantageous mutation arises, it will (if it survives the initial random walk) spread through the population in time only weakly dependent on the size of the population.

I think someone determined that every location in the human genome is being mutated in a newborn, somewhere on Earth, every generation. There are mutations more complicated than single nucleotide changes, of course.

[roseembolism.livejournal.com]

Another justification for Orion drive launch vehicles!

Note: I did not say GOOD justification for Orion drive launch vehicles, but their fans will take any excuse they can get.

[dbdatvic.livejournal.com]

And now I'm remembering one of those He Who Awoke-style novels from decades back (might be that one itself but I'd have to check) where the protagonist, traveling down the ages in slumber and waking once in a while to see what civilization looked like THIS million years later, had his sleeping-and-waking method depend utterly on enclosing himself in a deep rock formation with absolutely no radioactive particles or rays to disturb him, and being awoken by the release of Radioactive Rays from a gadget that also included a VERY long-term alarm clock.

(This of course doesn't work even in theory; he's got radioactive material inside himself inextricably, for one thing, and for another thing THE LIFE FORCE VRIL MATERIAL THAT KEEPS YOU UP AND AWAKE AND GOING DOES NOT WORK THAT WAY but hey.)

--Dave