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Can you give me an example of such a species ? Because I don't know any. The type of growth you're referring to would be like rabbits versus cats, and their num

by waps 13y ago

Can you give me an example of such a species ? Because I don't know any. The type of growth you're referring to would be like rabbits versus cats, and their numbers are anything but stable. And frankly, even if you can actually do that, give a stable species, the fact is that humans follow a pattern of massive expansion followed by large die-offs, rinse and repeat. http://en.wikipedia.org/wiki/File:World_population_growth_(lin-log_scale).png http://en.wikipedia.org/wiki/File:World_population_growth_(l... Note the logarithmic scale. Realize what it means if, on that graph, there is a very slight but visible drop. Note that "details" like the holocaust + all worldwide WWII victims simply don't register on that graph at all (events like that have been a near constant throughout history, just read what happened during islamic expansion in Europe over 700-800 years, with constant extermination campaigns usually, but not exclusively, by the invaders. And that's something that barely registers if you compare it to the islamic massacres in India). Then realize that this is a smoothed graph, where you wouldn't even see the majority of die-offs at all. The minimum you'd need to see it on that graph at all is a 10% die off, and that would be a flat horizontal line. Can you imagine a 10% die-off ? The minimum we'd need to detect it >200 years back, is a plague-sized event. There were lots of those, as you can see. That's the species we are. That's how our numbers have evolved. That's the reason evolution works. Still a fan ?

lutusp 13y ago
> Can you give me an example of such a species ? You need examples of species whose numbers aren't changing, but that are subject to the process of natural selection? Where shall I start? Well, there's one obvious starting point -- the fact that the theory of evolution models stable populations mathematically: http://en.wikipedia.org/wiki/Logistic_function http://en.wikipedia.org/wiki/Logistic_function > ... even if you can actually do that, give a stable species, the fact is that humans follow a pattern of massive expansion followed by large die-offs, rinse and repeat. You just answered your own question. From the standpoint of natural selection there's no difference between a species whose numbers don't change, and one whose numbers fluctuate up and down around a maximum defined by its environment. In any case, apart from humans there are thousands of species whose numbers are limited by their environments, and natural selection continues to choose which members of that species survive, based on the changing nature of the environment. This is evolution 101. > Still a fan ? What are you going on about? Do you or do you not want to understand evolution? You have already accepted, and given examples of, the idea that natural selection applies to growing populations and declining populations -- all you need to do now is fill in the blank space lying between the two.
- waps 13y ago
  I note you failed to actually illustrate species with stable numbers. What the logistic function has to do with anything, I don't know. When reading through the reason they choose this function to model population growth it is exactly to construct a stable population growth, not because this was observed in practice. And most certainly the human population curve looks nothing like the logistic function. It was going up much faster than the logistic function predicts. And the current slowdown of human population growth is so much faster than the ramp-up it's ridiculous to compare them. In the logistic function the slowdown mirrors the ramp-up. That's obviously not happening to humans. I can give plenty of popular examples of wildly fluctuating population numbers. Cats versus kangaroos/wallabies versus rabbits versus birds in Australia. Buffalo's versus beavers versus cats versus ... in Yellowstone park. Those are well studied examples of major flips in population density. I also grew up in an area with lots of farms, and I know that for example the number of wolves living in nature follows this pattern. Some years it is so bad they actually attempt to eat adult humans (and sometimes succeed), sometimes there are none. We had a rabbit problem while I was at university, and the biology department investigated. There was an exchange between the number of cats (ex-housecats) and the number of rabbits. First the cats would eat nearly all the rabbits, then they'd starve to the point that few cats remained (and human interference like milk bowls does indeed make things worse), after that the rabbit population multiplied in two years by a factor of more than 1000, after which the cat numbers started growing again. In all these cases you will observe massive swings in the population numbers. The swings were so large that just the swings themselves were at risk of making the species die off entirely (if a swing hits the number 1 or 0, the species never recovers, and has to be reintroduced. In practice that number is 9-10 according to the biology department. For rabbits or cats it never takes long for the species to be reintroduced of course). The biology department paper also claimed that while the timeframes vary wildly from species to species, these swings are the status-quo (within one habitat, the global population is more stable), not the exception. I do know this more from an algorithmic point of view, and I learn biology only as I need it, or if I'm bored or stuck. Which is why I asked you for a few examples of these stable population numbers, as I wouldn't really know. In genetic algorithms stable population numbers don't occur. Normally, because from time t -> t+1 you either let every current try duplicate n -> kn (higher k is better, but requires more resources), which is of course exponential growth. Then you kill all the ones that underperform (which is always basically all of them), or you select the k best performers. Or you can try to be smarter and model sexual reproduction, at which point you grow like n -> k n * (n - 1), which is even faster. There are plenty of variations, but almost all the ones I've ever seen work have exponential growth + 90%+ die offs. Even then genetic algorithms are disappointingly slow in most cases. On the plus side, genetic algorithms will find answers no other algorithm is able to find (much better coverage of the search space). However this comes at a truly massive cost in resources (as you would expect, but it'd be nice if it didn't). So you have an exponential growth, followed by a 99% dieoff (the number that die off has to increase the greater the population size becomes due to memory/cpu constraints).

by waps 13y ago

lutusp 13y ago

> Can you give me an example of such a species ? You need examples of species whose numbers aren't changing, but that are subject to the process of natural selection? Where shall I start? Well, there's one obvious starting point -- the fact that the theory of evolution models stable populations mathematically: http://en.wikipedia.org/wiki/Logistic_function http://en.wikipedia.org/wiki/Logistic_function > ... even if you can actually do that, give a stable species, the fact is that humans follow a pattern of massive expansion followed by large die-offs, rinse and repeat. You just answered your own question. From the standpoint of natural selection there's no difference between a species whose numbers don't change, and one whose numbers fluctuate up and down around a maximum defined by its environment. In any case, apart from humans there are thousands of species whose numbers are limited by their environments, and natural selection continues to choose which members of that species survive, based on the changing nature of the environment. This is evolution 101. > Still a fan ? What are you going on about? Do you or do you not want to understand evolution? You have already accepted, and given examples of, the idea that natural selection applies to growing populations and declining populations -- all you need to do now is fill in the blank space lying between the two.

waps 13y ago
I note you failed to actually illustrate species with stable numbers. What the logistic function has to do with anything, I don't know. When reading through the reason they choose this function to model population growth it is exactly to construct a stable population growth, not because this was observed in practice. And most certainly the human population curve looks nothing like the logistic function. It was going up much faster than the logistic function predicts. And the current slowdown of human population growth is so much faster than the ramp-up it's ridiculous to compare them. In the logistic function the slowdown mirrors the ramp-up. That's obviously not happening to humans. I can give plenty of popular examples of wildly fluctuating population numbers. Cats versus kangaroos/wallabies versus rabbits versus birds in Australia. Buffalo's versus beavers versus cats versus ... in Yellowstone park. Those are well studied examples of major flips in population density. I also grew up in an area with lots of farms, and I know that for example the number of wolves living in nature follows this pattern. Some years it is so bad they actually attempt to eat adult humans (and sometimes succeed), sometimes there are none. We had a rabbit problem while I was at university, and the biology department investigated. There was an exchange between the number of cats (ex-housecats) and the number of rabbits. First the cats would eat nearly all the rabbits, then they'd starve to the point that few cats remained (and human interference like milk bowls does indeed make things worse), after that the rabbit population multiplied in two years by a factor of more than 1000, after which the cat numbers started growing again. In all these cases you will observe massive swings in the population numbers. The swings were so large that just the swings themselves were at risk of making the species die off entirely (if a swing hits the number 1 or 0, the species never recovers, and has to be reintroduced. In practice that number is 9-10 according to the biology department. For rabbits or cats it never takes long for the species to be reintroduced of course). The biology department paper also claimed that while the timeframes vary wildly from species to species, these swings are the status-quo (within one habitat, the global population is more stable), not the exception. I do know this more from an algorithmic point of view, and I learn biology only as I need it, or if I'm bored or stuck. Which is why I asked you for a few examples of these stable population numbers, as I wouldn't really know. In genetic algorithms stable population numbers don't occur. Normally, because from time t -> t+1 you either let every current try duplicate n -> kn (higher k is better, but requires more resources), which is of course exponential growth. Then you kill all the ones that underperform (which is always basically all of them), or you select the k best performers. Or you can try to be smarter and model sexual reproduction, at which point you grow like n -> k n * (n - 1), which is even faster. There are plenty of variations, but almost all the ones I've ever seen work have exponential growth + 90%+ die offs. Even then genetic algorithms are disappointingly slow in most cases. On the plus side, genetic algorithms will find answers no other algorithm is able to find (much better coverage of the search space). However this comes at a truly massive cost in resources (as you would expect, but it'd be nice if it didn't). So you have an exponential growth, followed by a 99% dieoff (the number that die off has to increase the greater the population size becomes due to memory/cpu constraints).