Cicada Life Cycles: Why Evolution Chose Prime Numbers

[Gokul43201]

Know why the cicada have 13 and 17 year life cycles ? Is there a reason why evolution picked prime numbers for their life-cycles ?

Check out this neat article in the Post :
http://www.washingtonpost.com/wp-dyn/articles/A61426-2004May2.html

 

[loseyourname]

Evolution didn't pick anything.

 

[Gokul43201]

Evolution didn't pick anything.

No ? Who did ?

 

[Zurtex]

No ? Who did ?

Evolution is a theory not a person or a consciousness that chooses things. The theory of evolution goes that the most likely mutation to survive or reproduce the most will usually win. Or if the environment suddenly changes then only those suited will survive.

How do you see that as relating to prime numbers?

 

[loseyourname]

I remember hearing about the cicada lifespan at a lecture. There is some reason for it, but I can't remember what it is. I've searched online for you, but couldn't find anything.

Also, evolution doesn't always select the most fit organisms for survival. Especially during mass extinctions and bottlenecks, pure chance will often play a big role. Most of the time, though, the fittest will survive.

 

[hello3719]

not quite sure,
13 and 17 are longer cycles than those of the cicada's predators have cycles of 2 to 5 years ,the primality of 13 and 17 contributes to the fact that the GCD(to determine the intersection of the cycles) turns out to be a big number. ( 13 * 5 = 65 or 17 * 5 = 85)

 

[Parth Dave]

read the article.

 

[Gokul43201]

Evolution is a theory not a person or a consciousness that chooses things. The theory of evolution goes that the most likely mutation to survive or reproduce the most will usually win. Or if the environment suddenly changes then only those suited will survive.

How do you see that as relating to prime numbers?

Thanks for the primer, Zurtex. But I was not under the impression that Evolution was some all pervading genetic engineer that played around with everyone's genes to see what would make them survive better.

I think I know a little bit about evolution. Have we no poetic license in these forums ? Or should that be 'fora' ?

 

[Gokul43201]

Evolution is a theory not a person or a consciousness that chooses things.

PS : Evolution is a little more than just a theory. It is a very real phenomenon. It's happening continuously, and there is irrefutable proof for it.

Is 'disease' a theory ?

 

[matt grime]

"Forums" is better than "fora" these days. language is continually evolving, and forums is the more likely to be understood, conforms to the rules of English (English struggles to remember that it isn't latin some times), and is less likely to annoy people who see fora as overly fussy. Anyone who gets annoyed at fora not bing used probably thinks split infinitives are evil but doesn't know why. Having said that, I still won't accept data as a singlar noun.

 

[Gokul43201]

"Forums" is better than "fora" these days. language is continually evolving, and forums is the more likely to be understood, conforms to the rules of English (English struggles to remember that it isn't latin some times), and is less likely to annoy people who see fora as overly fussy. Anyone who gets annoyed at fora not bing used probably thinks split infinitives are evil but doesn't know why. Having said that, I still won't accept data as a singlar noun.

A data. Aarrgh !

 

[Zurtex]

PS : Evolution is a little more than just a theory. It is a very real phenomenon. It's happening continuously, and there is irrefutable proof for it.

Is 'disease' a theory ?

Correct me if I am wrong, but all things in science are theories, just with varying amounts of proofs and the ones with far more proof for them as apposed to proof against them tend to be the ones generally accepted. Also I always find being thorough in my posts is best, I was explaining to somebody the principles of general relativity and they ended up mistaking the word mass for meaning size and I had to write an even bigger post explaining it in far more detail.

 

[Gokul43201]

Zurtex,

I take back what I said. I was quibbling.

I was just a tad annoyed at what looked like a bunch of objections from people who never read the linked article in the first place.

 

[Gokul43201]

not quite sure,
13 and 17 are longer cycles than those of the cicada's predators have cycles of 2 to 5 years ,the primality of 13 and 17 contributes to the fact that the GCD(to determine the intersection of the cycles) turns out to be a big number. ( 13 * 5 = 65 or 17 * 5 = 85)

You mean LCM, don't you ?

 

[Zurtex]

Zurtex,

I take back what I said. I was quibbling.

I was just a tad annoyed at what looked like a bunch of objections from people who never read the linked article in the first place.

I'm sorry, I was more on the point of theory of evolution than the life cycles. It was just the way you worded your original question by saying "picked". For the actually mathematic of it, perhaps a point worth considering is that the LCM of the numbers a and b is ab if a AND b are co-prime. So perhaps the reason they are both primes is that when dealing with other cicada species.

 

[uart]

For the actually mathematic of it, perhaps a point worth considering is that the LCM of the numbers a and b is ab if a AND b are co-prime. So perhaps the reason they are both primes is that when dealing with other cicada species.

Which is exactly what the linked article says and exactly the reason why others have saying read the article before you start arguing semantics.

 

[Zurtex]

Which is exactly what the linked article says and exactly the reason why others have saying read the article before you start arguing semantics.

I'm sorry I did read it but in a bit of a rush, I only read that the cycles meet very rarely I didn't see that it went more into the mathematics than that.

 

[hello3719]

You mean LCM, don't you ?

lol
oops thanks for pointing it out
sorry for that
i make so much silly mistakes

and yea i forgot to read about the article,

 

[abertram28]

hahah... we have to argue about science and theory, evolution and genetic tendency... but the article points out that there is no direct evidence of any of the theories. that makes them hypothesies.

the article is terribly written, but conveys interesting thoughts. the article itself treats evolution as a separate being..

we all know that evolution doesn't take place unless the specifc action or even affects the sexual reproduction and effective raising of young. we might say that unless the effects that we analyze in this article are directly affecting the pre-sexual life then they are not evolutionary. if the affects directly impact the sexual relations then we might be more capable of calling it evolution.

anyways, as mere hypothesies, these things in this article might be as easily explained by chance instead of evolution.

if you look at the likelyhood that there was a time when the continent was completely covered with cicadas, or at least, the density was much much higher. before humans desicrated the land, obviously there was more animal and insect life. now there are more bacterial life... but i digress...

with such a large population of cicadas its understandable that there were groups of cicadas that had genetic mutations compared to others on different continents, and others within the same population. say just one cicada has a change in the genetics which dictate its frequency. say from an annual reproduction period to a bi-annual period. this mutation causes fluctuations in the population that affect all the cicadas. from this very first change in the population... the first year that there were a less cicadas because the mutation spread to a group the remaining cicadas without the mutation were eaten more. this meant that when the population with the mutation reappeared the following year they had a higher percentage of the population. this meant that the population that was non-cyclic was "chosen" by evolution, that evil man (btw, evolution only chooses those who die before sex, so being picked first aint that great), and the cicadas had to endure a year of a smaller population, but a higher percentage of cyclic genetics. after the first year of the mutation becoming more widespread, the cycles would interact. even just starting with an even population distribution youll get the modern result, given the method of survival, or the weapon against evolution, is strength in numbers. for the cicadas, this is basically its only defense. now, on the third year, most cyclic cicadas would have a good hybrid and there would be less of the initial cicadas. we can deduce that the likelyhood of the cicadas survival is directly linked to how many cicadas of that exact cycle come out. if very few cicadas in general come out, many will die. if there are many cicadas from a large variety of cycles existing at once, the hybridization will shorten the cycle, and thus, increase the likelyhood of death. if the initial drift was toward the 2 year cycle, on the off year, many would die, and in the next "on" year there would be an increased population of cyclic cicadas, but the hybridization would cause a distribution across the years, some would remain 1 year, but with the genes for two year. these would have the ability to create a 2 year offspring during the off years. there would be standard 1 years, that can only create 1 years. there would be 2 years ones with very dominant 2 year genes that would produce strong 2 year offspring. there would be 2 year "on" year cicadas producing 3 and 4 year cicadas, but with more spread dominance. these 3 year cicadas would come out with standard 1 year, and "off" 2 year cicadas, and these could begin to cycle, every other third year, every sixth year, they would come out with the 2 year dominant ones. during these years, the population would hybridize more. this continues until the populations hybridization creates an even spread of the mutation.

thats what leads to a widespread distribution of the cycle length. then, much later, environmental factors of each year cause cicadas to migrate slightly. if the "on" year 2 year cicadas were in the wrong cycle and it was too cold, they could be irradicated. the hybridization eventually causes the population to become unstable. certain cycles would be less likely to interfere. obviously, those are higher numbers, and prime numbers, with higher prime numbers being the most stable waves, and the short cycles being the most interfered with. you can see it would only take one or two major events to cause serious population drifts and isolations, and there were most certainly many events to cause such disturbances. variations in environment come in many flavors. the article illudes to the fact that the cold chose some species and not others, but i see it differently. i can imagine a cicada that is more stable being more widespread. the cicadas that are less stable in cycles would be more easily upset by rare events. the longer the period, the less likely a spontaneous event is to interfere. so the rare extra cold winters that occurred had less chance to deter the populations of longer period.. this has nothing to do with being prime.

the only thing that being prime allowed was what the article had right on. which is that the hybridization causes a drift in the population density distributed by year. odd number years interfered with even ones every other cycle. this would lead to a hybridization between the odd and even number, being most likely a year longer or shorter than the odd and even cycle. like if a 2 and 3 year population got together the most likely ones are 1,2,3,and 4. but some 5s would be created. if the 5s created emerge in 5 years, they obviously won't be on the same cycle as the parents, and they would be rare. if they survived, they would be more stable, but smaller in population. they would have more likelyhood of mating within the cycle and with others not on the same cycle. this would mean the hybrids would be more widely distributed, and thus more likely to die. the stability over time would allow the population to become larger, and more dominantly 5 year. if they became a 2 or 4 year cicada, they would interact with the parent species in a way that would adversely affect the entire population. if they were a 7 year interaction would be even less, and the likelyhood of a stable hybrid becomes less. as you go up, the likelyhood of a developed population becomes less, but the stability and dominance is greater. i can imagine if we were able to develop a strong wild strain of cicadas with a 19 year cycle that was a strong hybrid and dominant like the 13 and 17s, it would actually become on its own even more stable and dominant than the 17 or 13. its obvious that with the most infrequent interaction they have the most widely hybridized gene pools, mating between the 13 and 17 only occurs at 13*17. between 17 and any specific 2 year, 34 years! in 34 years the 2 years have undergone 17 generations! they are most certainly not the exact same after 34 years. if you look at the unique 3rd year ones its obviously a pattern that occurs no more often than every 34 years between truly cyclic cicadas.

thats why the populations are so strong, but so dominant and so pure.

im so sorry i just posted that long of a message.