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Evolution

Posted Feb 22, '13 at 3:29pm

aknerd

aknerd

1,431 posts

Evolution!

People LOVE to "debate" evolution. But that's silly, and doesn't really solve anything. If you are in a debate about whether or not evolution is a valid theory, you are either debating someone who has little to no idea what what evolution is, or ARE the person who has little to no idea what evolution is. That doesn't sound like very much fun, so let's not do that, okay?

Instead, this thread will be about topics in evolution, because it is much more entertaining to talk about specific cases and ideas than one big overarching theory. The topics will be chosen by whoever has the best topic, with all "lesser" topics being ignored and forgotten.

Now, I'll start us off with what actually made me want to start this thread: randomness. I was reading Mage's post at the bottom of this thread, and immediately thought about genetic drift.

Here is a classic example of genetic drift in a fruit fly population:

Basically, genetic drift states that random sampling has a lot to do with the evolution of small populations. Think about it: say you have a population of four individuals, two males and two females. One female homozygous allele for blue fur, the others all have a homozygous allele for red fur. Mating between blue and red fur produces a heterzygous purple fur creature. We would therefore expect the next generation to have some purple and red individuals, and the one after that to have all three colors represented. Basic Mendelian stuff.

Now, it gets interesting. Lightening strikes the blue female. She's dead, and will never reproduce. Now, all individuals in this population will be forevermore purely red. Note that this is regardless of the fitness of these genes. Blue fur might have been much more beneficial (perhaps these creatures lived in blue grass, and it provided camouflage), due entirely to random events (as opposed to evolutionary pressures) it is RED fur that becomes fixed in the population.

Going back to and contradicting Mage's comment from before, due to genetic drift, having the same selective factors won't guarantee a particular evolutionary outcome, due to simple random events.

So.... Discuss?

 

Posted Feb 22, '13 at 3:37pm

aknerd

aknerd

1,431 posts

(Its worth noting that my example is actually more about bottlenecking than genetic drift. Genetic drift typically refers to random sampling involving breeding/genetic recombination as opposed to random events involving death. But, in essence, they have the same result. Just adding this to avoid any later confusion)

Also, some conversation topics:

How important is genetic drift really? When is it important (ie, for which populations)? How big can the effects be?

 

Posted Feb 22, '13 at 3:51pm

HahiHa

HahiHa

5,820 posts

Moderator

Genetic drift doesn't lead to a smaller gene pool like bottlenecks. Bottlenecks really just mean that only a few genes gets passed on to the next generations (due to extinction events or migration) and those genes then build all of that population. Genetic drift means that the frequency of certain alleles change and replace other alleles over time. So no, not quite the same.

The effects of genetic drift can be that two populations, if separated, can evolve differently and form two distinct species over time. It is an important factor in long-time evolution.

 

Posted Feb 22, '13 at 5:54pm

MageGrayWolf

MageGrayWolf

9,798 posts

Knight

Going back to and contradicting Mage's comment from before, due to genetic drift, having the same selective factors won't guarantee a particular evolutionary outcome, due to simple random events.


The particular random event would also be a factor. This is what I meant when I said "If you were able to reproduce all the same selective factors" In such a case you would also have to reproduce the death of the blue furred female in order to reproduce all the selective factors involved.
 

Posted Feb 22, '13 at 8:09pm

aknerd

aknerd

1,431 posts

Genetic drift doesn't lead to a smaller gene pool like bottlenecks. Bottlenecks really just mean that only a few genes gets passed on to the next generations (due to extinction events or migration) and those genes then build all of that population. Genetic drift means that the frequency of certain alleles change and replace other alleles over time. So no, not quite the same.


Yes, the end result is. If only a few genes get passed on, then clearly the frequency of the genes is changing. The end result is that the population tends to move away from heterozygosity, though the mechanism is different (which is pretty much exactly what I said). In my example, the frequency of Blue alleles changed from .25 to 0 over time. A bit more sudden than in most genetic drift cases, to be sure. Don't worry, I'm putting in a better example later in this post.

The particular random event would also be a factor. This is what I meant when I said "If you were able to reproduce all the same selective factors" In such a case you would also have to reproduce the death of the blue furred female in order to reproduce all the selective factors involved.


Lightening is a selective factor? Usually, when we talking about selection, we mean selection due to environmental pressures such as competition for food. Its not like the blue furred creatures were especially attractive to lightening or anything. But no matter, I have a far better real life example!

Here's a graph and caption from a classic genetic drift lab experiment:

http://media.wiley.com/mrw_images/els/articles/a0001698/image_n/nfgz001.gif
Figure 1. The effects of genetic drift on 107 laboratory populations of the fruit fly, Drosophila melanogaster. The populations were maintained at a size of 16 individuals, giving a total of 32 possible different alleles (two per individual). The two horizontal axes respectively give the number of generations since the populations were all started (initial allele frequency of 0.5) and the number of mutant brown eye alleles in the population. The vertical axis reports how many of the populations possess that many alleles at a given time period. Looking across all 107 populations shows that genetic drift generates variation among the populations that increases with time, eventually ending in fixation of one or the other of the two alleles. Data from Buri (1956); figure from Hartl and Clark (1997).


So, in this experiment, we basically have 107 populations of fruit flies, that are then taken through 19 generations of breeding. Each population is maintained at 16 individuals. So basically, for each generation they would let all of the populations breed and produce eggs, then for the next generation they would randomly select 16 of those eggs out of each population to grow and become the next generation. And so on. What we see happen is that while the first generation tended to be well mixed for the eye color gene (white or brown), over time the populations moved to fixation, with the entire population being either entirely white eyed or brown eyed.

The point here is under the exact same environmental condition, some individuals populations became white eyed, and the others became brown eyed. This is because there was NO environmental pressure that determined eye color.
 

Posted Feb 22, '13 at 8:58pm

MageGrayWolf

MageGrayWolf

9,798 posts

Knight

Lightening is a selective factor?


Random doesn't really mean something doesn't have a pattern, just that the pattern is one in which we are unable to follow resulting in an uncertain outcome.

Its not like the blue furred creatures were especially attractive to lightening or anything.


The argument was that if we did the same things we would end up with the same results. There was an attempt to counter this with how we don't get this with evolution. However if all the same random events took place that influenced that species evolution (which would have to be included if we are doing all of the same things) you would end up with the same results.

I did admit that the reproduction of events at such a level is next to impossible. So let's just say for the sake of your argument I agree.
 

Posted Feb 22, '13 at 9:27pm

aknerd

aknerd

1,431 posts

However if all the same random events took place that influenced that species evolution (which would have to be included if we are doing all of the same things) you would end up with the same results.


How can it be a random event then, if it happens again the second time? I have had an example of this up on my about for a long time now.

When we look at things on the level of lightening striking, or the random selection in the fruit fly example, it no longer comes down to our ability to recreate an event, but rather or not there exists such a thing as true randomness. In other words, I feel like you are arguing that evolution is an example of causal determinism. I don't want to put words in your mouth, so correct me if I'm wrong on that point.

Actually, thats a far better topic of discussion than the current one:
Is evolution purely deterministic? Or, do some evolutionary events just... sort of happen for no reason?
 

Posted Feb 22, '13 at 10:05pm

Kasic

Kasic

5,746 posts

How can it be a random event then, if it happens again the second time? I have had an example of this up on my about for a long time now.

When we look at things on the level of lightening striking, or the random selection in the fruit fly example, it no longer comes down to our ability to recreate an event, but rather or not there exists such a thing as true randomness. In other words, I feel like you are arguing that evolution is an example of causal determinism. I don't want to put words in your mouth, so correct me if I'm wrong on that point.


Theoretically, if one were to know all the existing conditions, and I mean all of them, a lightning strike is not random. Nor are any other form of natural disaster. As for what gets caught where, if one had a perfect understand of how something would react to specific stimuli, predicting what something would do would be possible.

I saw theoretically, because as Mage said, that's so extreme it may as well be impossible, even if technically it is possible.
 

Posted Feb 22, '13 at 10:52pm

aknerd

aknerd

1,431 posts

Theoretically, if one were to know all the existing conditions, and I mean all of them, a lightning strike is not random.


And what theory, exactly is that? Lets suppose that we ignore all aspects of quantum physics that tell us that there are probabilistic forces at work which could change (ie randomize) the path of least resistance between the cloud and the ground, and thus the path of the lightening strike. Let's just set all that aside for now, and say no matter what, given the exact same conditions, the lightening strike will always happen the same way.

But.... what about the blue furred animal? Basically, you would have to make the claim that it has no free will, and will always be in the spot where the lightening hits it. Because if it had free will, then even with the exact same conditions, it might decide to meander somewhere else, and thus survive. What does free will have to do with evolution?
 

Posted Feb 22, '13 at 11:16pm

Kasic

Kasic

5,746 posts

And what theory, exactly is that?


I said theoretically, meaning technically possible but not really possible.

As I said, if we knew all of the factors, it would not be considered 'random.' I'm not saying it's actually possible.

Basically, you would have to make the claim that it has no free will, and will always be in the spot where the lightening hits it.


I would argue that free will doesn't really exist. At the most base level, we process stimuli and react biologically. The only reason we consider it free will is because it's so complex it may as well be that. If it were understood how someone would react when presented with any given stimuli, is that free will?

What does free will have to do with evolution?


This is the interesting point, philosophically. Did someone -choose- to perform a specific action which resulted in not dying, or were they simply responding to surrounding stimuli? Would they always react in that say way, if the exact same conditions took place? I believe that they would.
 
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