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Author Topic:   What is the mechanism that prevents microevolution to become macroevolution?
RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 28 of 301 (344858)
08-29-2006 7:15 PM
Reply to: Message 21 by Equinox
08-29-2006 12:57 PM


bottlenecks
Wow, this is an easy to understand, powerful test. Biologists can find and approximately date past bottlenecks as RickJB gave an example of. A bottleneck often reduces a population down to just a few hundred or thousand individuals.
We could start by listing all the species that we know had bottlenecks and then see how the data cluster for those species.
For instance there is evidence of a human bottleneck ~100,000 years ago:
BBC - Human Bottleneck Evidence (click)
Clues from genetics, archaeology and geology suggest our ancestors were nearly wiped out by one or more environmental catastrophes in the Late Pleistocene period. At one point, the numbers of modern humans living in the world may have dwindled to as few as 10,000 people.
"Our data suggests there was a bottleneck that was not that recent," says Goldstein. The genetic data puts the likely date for this event at just before 100,000 years ago.
And then from
The population bottleneck, supervolcanoes and the coming end of the world - Everything2.com
For example, Lynn Jorde and Henry Harpending 2 from the University of Utah have studied the patterns of mitochondrial DNA (mtDNA) within the human population and have concluded that it is consistent with a dramatic reduction in population size at some point in our past, which they calculate occurred roughly 70-80,000 years ago when the human population was reduced to as few as 5 or 10,000 individuals.
... it is believed that the last supervolcano to erupt was at Toba in Sumatra, the biggest volcanic eruption the world had ever seen, 10,000 times the size of the 1980 Mount St. Helens eruption, blowing a big 100 kilometres by 60 kilometres hole in the earth that is now known as Lake Toba.
And when did this happen? 74,000 years ago, right within the 70 to 80,000 year time frame that messrs Jorde and Harpending believe that the human population bottleneck occured.
Also see
Toba catastrophe theory - Wikipedia
Anyone know when the cheetah bottleneck occurred?
Enjoy.

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This message is a reply to:
 Message 21 by Equinox, posted 08-29-2006 12:57 PM Equinox has not replied

Replies to this message:
 Message 29 by jar, posted 08-29-2006 7:22 PM RAZD has not replied

RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 50 of 301 (345167)
08-30-2006 6:49 PM
Reply to: Message 32 by Faith
08-29-2006 8:32 PM


are bottlenecks tied to speciation?
THAT'S WHAT SPECIATION DOES, IT SEVERELY REDUCES GENETIC DIVERSITY. That's what a bottleneck is, severely reduced genetic diversity.
I don't think these - speciation and bottlenecks - are necessarily related.
Speciation may cause a bottleneck, if it is of the founding population variety and the population is small.
A bottleneck event may cause speciation, as in the Yucatan meteor extinction event and the subsequent rapid speciation of many types to fill the voids left by extinct species (most well know would be foraminifera)
But does one necessarily follow from the other?
If the bottleneck is caused by a random event that does not select one set of genes over others, it could leave behind nearly as much diversity as there was before, diversity that would be quickly recirculated into the population as a whole, and the missing amount made up with subsequent mutation rates, but the population could still be the same species generations after the bottleneck event has passed.
If speciation occurs in a whole population through drift over time then there is no bottleneck involved and the amount of diversity in any one generation is the same as the one before and after.
Or speciation where a population divides into two or more subpopulations that no longer mate -- there is no loss in diversity there, as it is divided between the two populations.
There are other factors involve that make a strict relationship problematical, imh(ysa)o.

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This message is a reply to:
 Message 32 by Faith, posted 08-29-2006 8:32 PM Faith has replied

Replies to this message:
 Message 68 by Faith, posted 09-01-2006 4:09 AM RAZD has replied

RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 88 of 301 (345859)
09-01-2006 9:30 PM
Reply to: Message 68 by Faith
09-01-2006 4:09 AM


Re: are bottlenecks tied to speciation?
interesting strikeouts.
What I'm saying is that a bottleneck is simply an extreme version of a number of the selecting and population-splitting processes that cause new traits to appear in the phenotype
The question is whether it must always result in this. I don't think so.
Speciation may cause a bottleneck, if it is of the founding population variety and the population is small.
But a founding population IS like a bottleneck and it's the bottleneck or founder effect that is causing the speciation, not the other way around.
What I'm arguing is that this is one case where they are related, there are others I give where they aren't.
Well, I suppose it's possible that the bottleneck simply might select out the very alleles that are already most expressed in the population and there would be little phenotypic change. I can't think of another way this might happen.
It may make no selection of alleles at all. Think of a population of 10,000 individuals and 1 in 10 survive a random catastrophe by luck not genetics\selection -- they just happened to be in the right place.
The distribution of alleles in both populations is the same, both in kinds of alleles involved and in their relative number -- say a bell curve distribution -- so that the shape of the distribution is the same, just the total population is reduced. The result is the same degree of diversity (the same bell curve) just fewer individuals.
The species will still have the same distribution of alleles.
Yes, drift is the situation of no population split which we've been acknowledging may change the phenotype without reduction in diversity. It's the natural playing out of changing allelic frequencies in the population that brings this about in this case.
Speciation without bottleneck, bottleneck without speciation, therefore not necessarily related. It's like a grid:
----------------------------------
| no-speciation | speciation |
| bottleneck | bottleneck |
----------------------------------
| no-speciation | speciation |
| no-bottleneck | no-bottleneck |
----------------------------------
Any population can fall into any one of those four quadrants at different times.
There are other factors involve that make a strict relationship problematical, imh(ysa)o.
Only mutation. Nothing else.
No, mutation has no bearing on whether population fall into one quadrant or another -- there are other factors that affect which quadrant they are in that can override any relation between speciation and bottlenecks. The only way that a strict relationship could exist is if two corners of the grid could not be populated with different species at different times.
But there is definitely a loss of diversity IN the subpopulations and this is what we are talking about. If they can't interbreed then they can't recombine their alleles so the diversity they share between them is meaningless.
It does NOT reduce the diversity in the total population of life on the planet, and it allows the now separated populations to expand their population diversity with subsequent mutation, thus ending up with more diversity than the total population of life on the planet started with: that is the issue.
So there does seem to be this idea that speciation CAUSES bottlenecks.
That is the other problem with the supposed relationship - in some cases {A} can happen before {B} and in some cases {B} can happen before {A}. That makes it hard to show that {A} causes {B} eh?
  • some speciations cause bottlenecks in daughter populations
  • some speciations don't cause bottlenecks in daughter populations
  • some bottlenecks cause speciation
  • some bottlenecks don't cause speciation
    Conclusion: bottlenecks and speciation are not necessarily related events.
    Enjoy.

  • This message is a reply to:
     Message 68 by Faith, posted 09-01-2006 4:09 AM Faith has replied

    Replies to this message:
     Message 145 by Faith, posted 09-04-2006 9:02 PM RAZD has replied

    RAZD
    Member (Idle past 1405 days)
    Posts: 20714
    From: the other end of the sidewalk
    Joined: 03-14-2004


    Message 254 of 301 (347857)
    09-09-2006 8:37 PM
    Reply to: Message 145 by Faith
    09-04-2006 9:02 PM


    Re: are bottlenecks tied to speciation?
    Thought I better get to this before the thread is closed for the 300 limit.
    Well, I'm trying to avoid being all that strict, I'm trying to argue a TREND here, a trend TOWARD speciation that involves ...
    Only looking at the data that fits the trend you want to find? Isn't that begging the question? No, you need to look at all the evidence and if the trend is clear you have something, if it is a football shaped scatter of points you have an indication of a trend but it is obscured by other factors and it could be totally unrelated.
    I don't know why you are focused on a "strict relationship" since I've been trying to say that this is trend, ...
    That's what a strict relationship is -- a trend that clearly shows in the data.
    Otherwise you have some data that meets your trend and some data that doesn't meet your trend, and then you have to deal with the data that doesn't meet the trend in order to show that the trend has any predictive value. If you can't predict when a result will be on the {general sort of trendish kinda line maybe) trend and when it will be totally off in some other corner, then you can't predict a result from the trend you've selected.
    The idea that mutation now takes over and produces new alleles is pure fantasy, ...
    Denial of evidence does not make it go away. You can measure the frequency of alleles in a population before speciation and again several generations afterwards, after a series of mutations have occurred, and you get new alleles showing up, ones that were not in the original population: where do they come from? Mutations.
    Well, but the whole point of the bottleneck (and founder effect) example is that it is not at all likely that you would get anything like the same distribution as was in the original population, because the new population is so much smaller.
    We are not talking about situations where one end or the other of a distribution of alleles was selected by a survival event, but one where the survival was completely random and not based on any genetic advantage or disadvantage.
    And the probability is that the individuals will be randomly selected in proportion to their existing distribution of alleles, so the 'bottleneck' population will have the same distribution.
    Think of how public polls are conducted, and consider each question on a poll to be a gene and each possible answer is an allele variation.
    Pollsters claim (based on the mathematics of population distributions) to be able to sample a thousand people and represent the opinions of ~300 million (american) people with something like a 5% error, right?
    http://www.ropercenter.uconn.edu/pom/polling101.html
    In other words, the allele distribution in the 'bottleneck' population (the thousand that were polled with the questions) represents 95% of the opinion allele distribution of the full population (of ~300 million americans) -- and the error doesn't mean that some opinions were NOT expressed, just that some of them were NOT expressed in the same proportion as in the total population -- they are still there in the 'bottleneck' population.
    some speciations cause bottlenecks in daughter populations
    some speciations don't cause bottlenecks in daughter populations
    some bottlenecks cause speciation
    some bottlenecks don't cause speciation
    Conclusion: bottlenecks and speciation are not necessarily related events.
    Um, I hope the above has clarified what I was saying since none of this represents it.
    Which then is why your thinking is not valid as a representation of all the possiblities. I'll make it simpler:
  • sometimes bottlenecks and speciations occur together, and sometimes they don't
  • when they do both occur, sometimes one comes before the other, and sometimes the other happens first
  • CONCLUSION: there is no relation whereby a bottleneck OR a speciation event - alone - can predict whether the other also occurs.
    There are other factors that are involved that have as much or more to do with whether speciation occurs or whether there is a bottleneck event.
    Hope that helps.

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  • This message is a reply to:
     Message 145 by Faith, posted 09-04-2006 9:02 PM Faith has replied

    Replies to this message:
     Message 255 by Faith, posted 09-09-2006 11:16 PM RAZD has replied

    RAZD
    Member (Idle past 1405 days)
    Posts: 20714
    From: the other end of the sidewalk
    Joined: 03-14-2004


    Message 277 of 301 (347997)
    09-10-2006 8:59 PM
    Reply to: Message 255 by Faith
    09-09-2006 11:16 PM


    Re: are bottlenecks tied to speciation?
    You aren't really thinking about the situation of a sharply reduced population.
    Opinions aren't like alleles. Bottlenecks don't "sample" a population.
    Only 1000 out of 300,000,000 is not a sharply reduced population???
    That's 0.00033% of the original population.
    The population after a bottleneck event is nothing less than a sample of the population before the bottleneck event.
    And that leaves mutation as THE ONLY process that MIGHT actually add new information.
    I'll assume (in the absence of any metric being provided to quantify and measure "information" in any kind of genetic sense) that novel behavior would be evidence of "new" information -- new as in never seen before behavior based on a genetic change ... and we have the nylon eating bacteria, bacteria that have evolved to eat a substance (a) they could NOT consume when it was first introduced and (b) did not EXIST before man created it.
    I expect you'll quibble on this, but when you do: have a metric that measures the "information" content otherwise it is just opinion.
    You seem to think that a mutation that just moves DNA from one place to another cannot create new information in the process. Consider these phrases (1):
  • Woman, without her man, is nothing.
  • Woman, without her, man is nothing.
    I think you'll agree that the second phrase has a whole 'new' meaning that was not contained in the first even though all that was moved was one comma. How was this "new" information introduced eh?
    Please supply evidence of this. ... Show me these brand new alleles in this completely isolated population that has no gene flow with other populations of the same species.
    Again, we have the nylon eating bacteria, the alleles that allow them to consume this material did not exist before they evolved this capability.
    I expect you'll quibble on this, but it doesn't really matter: life will go on evolving regardless of your opinion on the matter.
    I never said there was, RAZD. Please quote where you think I said that. I remember saying clearly that of COURSE bottlenecks don't ALWAYS cause speciation -- or even always eliminate alleles.
    You seem to regard this Message 50 issue as only in response to your pet theory, when it has been more concerned with the lack of relation between bottleneck and speciation -- reread the linked post. I was (heh) introducing "new" information ... k?
    Enjoy.

    (1) - from old Stone Soup Cartoon, the Mom was teaching the teenage Holly the importance of punctuation.
    (Today on Stone Soup - Comics by Jan Eliot - GoComics)

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    we are limited in our ability to understand
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    RebelAAmericanOZen[Deist
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    to share.

  • This message is a reply to:
     Message 255 by Faith, posted 09-09-2006 11:16 PM Faith has replied

    Replies to this message:
     Message 279 by Faith, posted 09-10-2006 9:37 PM RAZD has not replied

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