Mutation with magnetic field reversals

[Loren Booda]

Here is another question (the previous one about meteor impact) concerning extraterrestrial effects upon terrestrial selection:

Could the incidence of mutations increase substantially during times of magnetic pole shifts? The unstable Van Allen belts then might allow more radiation to reach the Earth, causing periods of accelerated genetic evolution. Likewise, do magnetic field reversals correspond to times of speciation, or vice versa?

 

[Reality_Patrol]

I think that is a fantastic question. I prefer to refer to speciation as evolution. Natural selection doesn't seem to offer a compelling explanation of speciation in my view. Natural selection does offer a compelling explanation of adaption.

With that personal bias in mind, I've looked for environmental triggers that might lead to speciation events (evolution). I use the term "evoluationary zeitgebers". Today we know that means major changes to the DNA. How would this occur naturally though?

Well, one theory that's been discussed here recently has suggested high temperatures. That leads to a cascade of cellular events that result in mutations. Another indisputable modifier of DNA is radiation. So, perhaps you've hit on something. If a magnetic pole reversal allowed in more cosmic (i.e. non-solar) radiation than the present levels, real affects on DNA across many species would happen simultaneously. Most interesting. Thanks for the post.

 

[Evo]

That is a great question. I had watched a program about the reversal of the Earth's magnetic fields and they discussed the impact of it on animals that rely on the Earth's magnetic fields for migration. The question was, would it lead to mass extinction? Here is just a blurb on it, apparently it takes so long for the poles to flip that there is no record of "sudden" change which seems evident from past flips, but certainly there could be more subtle long term changes.

"Indeed, the researchers I spoke with all thought that organisms would be able to adjust to an acute weakening or even complete reversal of the magnetic field. "My gut reaction is it's not going to have an impact," says Frank Paladino, the Indiana-Purdue University leatherback researcher whose project I was visiting that night in 1993.

History seems to back this up. There is no firm evidence that the many magnetic field reversals that have taken place throughout our planet's history (see When Compasses Point South) have coincided with or triggered extinctions. Reversals take hundreds if not thousands of years to complete, and because for anyone type of animal that represents hundreds or thousands of generations, species have time to accommodate to the change. Moreover, Kirschvink notes that even if the main dipole field were to collapse—an event that can last for up to 10,000 years during a reversal—residual fields 5 or 10 percent as strong as the main field would remain on the surface, and animals would be able to use those quite well for migration."

http://www.pbs.org/wgbh/nova/magnetic/animals.html

There is also a timeline of all of the flips here http://www.pbs.org/wgbh/nova/magnetic/timeline.html

 

[Mk]

A geomagnetic excursion would definitely be responsible for increased incidence of mutations. I have no idea how much more though. Much more cosmic radiation would be let through.

 

[Ophiolite]

I don't see any logical way in which a geomagnetic reversal is going to lead to an increase in mutations. I stand ready to be corrected Mk.

The van Allen belts are composed primarily of trapped electrons and protons from the solar wind. Remove the van Allen belts completely and the upper layers of the atmosphere will absorb those charged particles. Net effect on the biosphere, nil.

Cosmic rays that are coming in with sufficient energy to generate muon showers are not going to be significantly deflected by the magnetic field.

Electromagnetic radiation is unaffected. The nasty part for biological entities, ultra violet and higher, is stopped by the atmosphere, not by the magnetic field.

What am I missing?

 

[Loren Booda]

I believe one of the conditions for life flourishing on Earth is the deflection of mutanogenic charged particles by a substantial magnetic field. The atmosphere itself may not be effective enough in this regard to maintain advanced life over long periods.

 

[Mk]

Check this very closely-related thread: https://www.physicsforums.com/showthread.php?t=114191

 

[Ophiolite]

I checked the thread, to which I had already contributed, and still fail to see what I am missing. I have long assumed that the magnetic field was shielding us from harmful radiation, but when you look at it in detail, I fail to see what radiation it is shielding us from. Please elucidate MK.

 

[Reality_Patrol]

Given that cosmic rays are mostly charged particles the Lorentz force law supplies the answer. Any charged particle with a velocity vector directed towards the earth, will experience a Lorentz force at a right angle in the presence of the terrestial B field. Thus the incoming particle will be deflected to some extent. The force is linearly proportional to the strength of the B-field, so as it weakens the deflecting force does likewise. The result of all this is more particles will make it to the earth.

 

[Ophiolite]

Two questions:
1. Given the high velocity of cosmic rays would you think the linear displacement of these would be significant. My argument is that they would not be.
2. I would have thought that at present the field deflects some particles that would have missed the Earth, so that they strike it. With the field weakened or absent these would now miss. My perception is that these two effects would balance out. What do you think?

 

[Reality_Patrol]

1. Well the actual amount of displacement depends on more than just the field strength. The full displacement also depends on the distance over which the deflecting force is exerted. This is in turn determined by the distribution of the B-field. In principle the deflecting force we're speaking of begins exerting itself at any location in space where the particle's velocity vector becomes directed towards earth. This is because the terrestial B-field extends to infinity. That's sounds rather philosophical but it really isn't. A numerical simulation would model the B-field as far into space as it was possible to compute with. This means the computational capability of the computer would set the "effective distance" of the terrestial B-field in a numerical simulation of the scenario we're discussing. In any case the force is exerted over a great distance. So, even though it's weak it's net effect is appreciable.

2. No. You're thinking that some particles that aren't directed towards the Earth can become deflected towards the Earth as a result of the B-field. Charged particles follow curved trajectories under the influence of a B-field in general, not straight lines. So at first what you're thinking could happen but the field would continue to deflect it, eventually pointing it away from the earth. It must do this, otherwise the result of the field would be a velocity vector for the particle directed towards the Earth which contradicts the Lorentz force law (per my original answer).

 

[Danniel]

Would not it primarily affect rates of cancer incidence, rather than rates of evolution?

Since lots of organisms have differentiation between somatic and germ cells, having more somatic than germ cells, and spending more lifetime doing other things than reproducing. However for those species which do not have much differentiation, like bacterias I guess, and organisms that reproduce by fragmentation, mutation in somatic cells would affect their evolution.

I think it would (primarily affect rates of cancer incidence), if magnetosphere really is effective to hinder any sort of radiation that would cause mutations. But apparently if anything in this sense happens, it is not even at a level of causing mass extinctions.

 

[quantumcarl]

Would not it primarily affect rates of cancer incidence, rather than rates of evolution?

Since lots of organisms have differentiation between somatic and germ cells, having more somatic than germ cells, and spending more lifetime doing other things than reproducing. However for those species which do not have much differentiation, like bacterias I guess, and organisms that reproduce by fragmentation, mutation in somatic cells would affect their evolution.

I think it would (primarily affect rates of cancer incidence), if magnetosphere really is effective to hinder any sort of radiation that would cause mutations. But apparently if anything in this sense happens, it is not even at a level of causing mass extinctions.

This is where I'm missing this thread's definition of "natural selection" and "speciation". Even if there were periods where there was an environment of higher radiation, those affected populations of species would either adapt or die off in the face of the increased radiation. This is why its called "natural selection": One portion of a species mutates in a manner that helps it survive a certain environmental condition (this is how it is "selected" to survive) and one portion of the species develops an inefficient mutation that eliminates them from the short list of selection (possibly because of a cancerous mutation or some other "incorrect" genetic response to the event).

Is it not true that natural selection is the mechanism behind speciation? And isn't it true that this would be true in the case of impact events, higher-than-normal radiation surges or what-have-you?

In the case of any traumatic environmental event isn't it the biological (ie: genetic) response of any organism that determines whether it will develop (ie: evolve into) a new species via its randomly occurring mutations that result in its survival? This automatically allows a specific portion of a species to adapt to new, challenging conditions (ie: be "selected") and form a "new" species out of those traits. Mean while, the rest of the former species is left behind, fertilizing the development of the species it has become.

That's how I see in anyway.

The sequence goes:

species + environmental event + natural selection of beneficial mutations = speciation.

 

[Reality_Patrol]

Would not it primarily affect rates of cancer incidence, rather than rates of evolution?

Yes.

But apparently if anything in this sense happens, it is not even at a level of causing mass extinctions.

Quite the contrary, high rates of cancer - species wide - would cause mass extinctions. Presumably though beneficially mutated offspring would survive. Whether the mechansims occurs through (mutual) germ cell mutations or fertilized egg cell mutations is unknown of course. In any case these sudden and extreme mutations could indeed be a speciation event if severe enough.

That's the difference really, in my answer to QC's questions. The mutations would have to be extreme enough such that the offspring born during the traumatic event really couldn't reproduce with other members of the parent species born before the event. More simply the structure of the offsprings mutated genome would have to be in some fundamental way incompatible with the parents.

Natural selection would determine whether the changes are beneficial or not, of course, but doesn't really initiate the event per se.

 

[Danniel]

Quite the contrary, high rates of cancer - species wide - would cause mass extinctions.

... I do not deny that a considerable elevation in rates of cancer would cause mass extinctions... what I meant is that, since mass extinctions do not seem to appear together with the nullification of magnetosphere between magnetic reversals, apparently it is not causing a significative increase in rates of mutations, and having no significative effect on evolution whatsoever.

That's the difference really, in my answer to QC's questions. The mutations would have to be extreme enough such that the offspring born during the traumatic event really couldn't reproduce with other members of the parent species born before the event. More simply the structure of the offsprings mutated genome would have to be in some fundamental way incompatible with the parents.

Could be more indirect than that; combining smaller mutations, and populational decrease due to cancer and other events of population genetics that would likely follow, such as drift, founder effect, bottleneck, according with each species particularities, and how closer they are to the Equator (presumably more affected)... that would make some mess, creating new genes, shuffling the already existing while spliting populations, opening new niches, etc.

Summarizing, rather than a direct mutationist-saltationist scheme like:

radiation -> mutation -> speciation

it could be:

radiation -> mutation -> populational decrease through cancer and unfit mutations for some -> ecological mess/populational genetics consequences -> speciations

 

[Danniel]

This is where I'm missing this thread's definition of "natural selection" and "speciation". Even if there were periods where there was an environment of higher radiation, those affected populations of species would either adapt or die off in the face of the increased radiation. This is why its called "natural selection": One portion of a species mutates in a manner that helps it survive a certain environmental condition (this is how it is "selected" to survive) and one portion of the species develops an inefficient mutation that eliminates them from the short list of selection (possibly because of a cancerous mutation or some other "incorrect" genetic response to the event).

I´m not sure if the survivors of mass extinction episodes fit well as naturally selected; yet that is semantically arguable that it would be a sort of natural selection, in population genetics it would be more adequately considered bottleneck effect or founder effect, unless, whatever the factor of mass extinction was, it made possible to organisms with some very specific set of traits to survive. I.e., some radiation-resistant bacteria would be truly selected in this scenario of increased radiation, but those that survived simply because had the happen of not having highly deletereous mutations caused by the radiation, are not being selected according with the jargon; it was a matter of luck, there was no "merit" of any trait in the survival. Eventual beneficial mutations conferred by this raising of radiation would be considered to be naturally selected or not according with the difference that it made to a certain trait, comparing with the normal, non-mutated trait, in its adaptation. Again, this individual that was twice lucky is not considered to have been selected by the radiation event; the radiation event more frequently does not select, but sorts, unless it´s something about radiation-resistance.

Is it not true that natural selection is the mechanism behind speciation? And isn't it true that this would be true in the case of impact events, higher-than-normal radiation surges or what-have-you?

Depends on the concept of the species in each case... there are species, which are more properly called ecological species, which can yet interbreed with closely related species and generate fertile offspring. They differ more in some specific adaptative traits, adapted to a certain niche, and are "ecological" species because of that. Galapago´s finches, and lots of bees are examples. That's why almost all the American bees are africanized bees, because African bees were brought to South America and accidentally spread along the continents, crossbreeding with local varieties.

Natural selection is primarily the cause of adaptative change; populations that evolve different adaptations may eventually, gradually, became less fertile with each other, both because the populations do not need to interbred anymore and differences interferring with the viability between hybrids are not selected out, and because further diverging adaptation may actively hinder the hybrid viability. Then the fate of ecological species, if teared apart by adaptation enough, is to become trye biological species.

At the same time, physiological speciation, where one species cannot breed producing fertile offspring with related (biological, not ecological) species, can occur just by chance, not preceded by adaptative change, and retain two barely changed biological species made out of one. They may be ecologically forced to divert adaptatively then, or one of them could become extinct, if they´re adapted to a very specialized niche and still inhabit the same (limited) habitat.

 

[Danniel]

BTW, somewhat related news:

Taking evolution’s temperature: Researchers pinpoint the energy it takes to make a species
Filed under Research, Health, Environment, Sciences on Wednesday, May 31, 2006.

GAINESVILLE, Fla. — Comfortable living is not why so many different life forms seem to converge at the warmer areas of the planet.

Writing this week in the Proceedings of the National Academy of Sciences, scientists say higher temperatures near the equator speed up the metabolisms of the inhabitants, fueling genetic changes that actually lead to the creation of new species.
...


http://news.ufl.edu/2006/05/31/biodiversity-2/

Do not agree quite much because of similar reasons, seems that from higher mutation rates cancer is also a increased risk, and for explaining equatorial biological richness, I think that simple answer that the more light feeds more plants, creating a wider base of a ecological pyramid, a more aboundant environment, is already enough to permit more variations to not be selected out...

 

[quantumcarl]

I´m not sure if the survivors of mass extinction episodes fit well as naturally selected; yet that is semantically arguable that it would be a sort of natural selection, in population genetics it would be more adequately considered bottleneck effect or founder effect, unless, whatever the factor of mass extinction was, it made possible to organisms with some very specific set of traits to survive. I.e., some radiation-resistant bacteria would be truly selected in this scenario of increased radiation, but those that survived simply because had the happen of not having highly deletereous mutations caused by the radiation, are not being selected according with the jargon; it was a matter of luck, there was no "merit" of any trait in the survival. Eventual beneficial mutations conferred by this raising of radiation would be considered to be naturally selected or not according with the difference that it made to a certain trait, comparing with the normal, non-mutated trait, in its adaptation. Again, this individual that was twice lucky is not considered to have been selected by the radiation event; the radiation event more frequently does not select, but sorts, unless it´s something about radiation-resistance.

Depends on the concept of the species in each case... there are species, which are more properly called ecological species, which can yet interbreed with closely related species and generate fertile offspring. They differ more in some specific adaptative traits, adapted to a certain niche, and are "ecological" species because of that. Galapago´s finches, and lots of bees are examples. That's why almost all the American bees are africanized bees, because African bees were brought to South America and accidentally spread along the continents, crossbreeding with local varieties.

Natural selection is primarily the cause of adaptative change; populations that evolve different adaptations may eventually, gradually, became less fertile with each other, both because the populations do not need to interbred anymore and differences interferring with the viability between hybrids are not selected out, and because further diverging adaptation may actively hinder the hybrid viability. Then the fate of ecological species, if teared apart by adaptation enough, is to become trye biological species.

At the same time, physiological speciation, where one species cannot breed producing fertile offspring with related (biological, not ecological) species, can occur just by chance, not preceded by adaptative change, and retain two barely changed biological species made out of one. They may be ecologically forced to divert adaptatively then, or one of them could become extinct, if they´re adapted to a very specialized niche and still inhabit the same (limited) habitat.

Thank you for your last two posts these are very enlightening and show me that I can't generalize about environmental influence on speciation.

From Wicpedia:

Speciation is the evolutionary process by which new biological species arise. There are five main concepts concerning the emergence of new species (modes of speciation), each based on the degree to which populations undergoing this process are geographically isolated from one another (allopatric, peripatric, parapatric, sympatric, polyploidy).

A good example would be found in the aquatic ape hypothesis of Sir Alister Hardy. These apes separated from the savannah-type apes and followed fresh river water and its food sources to the ocean where they found year round food.

This isolation from their group speciated them. The seafood they ate benefited the development of the brain. And the bouyancy of the ocean led them to stand upright... as well as lose body hair and develop a nose more efficent for keeping out water while swimming in it.

Presented by Sir David Attenborough Scars of Evolution is a two part series looking at the history and current status of the 'aquatic ape hypothesis' (AAH), first proposed 45 years ago by Sir Alister Hardy, then elaborated and developed by Elaine Morgan and others.

The hypothesis proposes that the physical characteristics that distinguish us from our nearest cousin apes - standing and moving bipedally, being naked and sweaty, our swimming and diving abilities, fat babies, big brains and language - all of these and others are best explained as adaptations to a prolonged period of our evolutionary history being spent in and around the seashore and lake margins, not on the hot dry savannah or in the forest with the other apes.
Here's what Richard Attenbourogh wrote about that hypothesis:

From: http://www.bbc.co.uk/radio4/science/scarsofevolution.shtml

Not much to do with instant mutation. But imagine the gradual mutations taking place over, say, a million years while these bi-pods hung-out on the beach!

I'm glad this theory has gained some acceptance in the real world since it pretty well answers every question to do with our evolution, adaptation and appearance. The nay-sayers are, for the most part, closet "creationists" who possesses a dash of "intelligent design" for good measure.

The Aquatic Ape idea also holds the potential to become the "missing link". This is because the only evidence of this species would be their descendents. They're personal remains are no longer available... having been mostly washed out to sea or eaten by seagulls and Orcas.