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Author Topic:   How many generations does speciation take?
custard
Inactive Member


Message 1 of 52 (188812)
02-26-2005 9:52 PM


I'm not sure how to phrase this question, so I'll just come out and ask it.
Assuming the following:
1- Common decent from a single species
2- Rate/frequency of mutation is constant for all species
3- No evolutionary stasis/stagnation - i.e. a species does not remain unchanged for 60 million years
4- No cataclysmic events wiping out significant numbers of species.
To draw a clear, unequivocal line between species I want to use the following, restrictive definition of speciation (from talk origins), which as Pink Sasquatch has pointed out is NOT the currently accepted version of BSC:
"... that stage of evolutionary progress at which the once actually or potentially interbreeding array of forms becomes segregated into two or more separate arrays which are physiologically incapable of interbreeding." (Dobzhansky 1937)
It is important to note that this is a highly restrictive definition of species. It emphasizes experimental approaches and ignores what goes on in nature.
How many generations of offspring would have to be produced to achieve a similar level of speciation we see today - say 50 million species- from a single (Alpha) species over 3.5 billion years?
This question arises as a result of several things I have read recently: Jay Gould's Structure of Evolutionary Theory, some stuff on neo-darwinism, Haldane's dilemma, and from some things I've seen in ongoing threads that keep using analogies such as "imagine evolution is a walk down the street from house A to house G and the fossil record is a series of snapshots..." implying a gradual rate of mutation that leads to eventual speciation.
I realize this question might seem very open ended, but I'm just looking for a hypothetical mathmatical model that I can use as a starting point to help me understand how frequently mutations need to occur, and how frequently speciation needs to occur, for a Common Decent model of evolution to work.
I couldn't find anything this specific, in this forum, but if this has been explored in other threads, or if you know of links that would be helpful, please point the way.
Thanks.
This message has been edited by custard to actually add the definition of speciation I keep referring to , 02-26-2005 21:57 AM
This message has been edited by custard, 03-03-2005 17:13 AM

Replies to this message:
 Message 3 by pink sasquatch, posted 02-27-2005 5:14 PM custard has replied
 Message 33 by Brad McFall, posted 03-03-2005 5:06 PM custard has replied

  
custard
Inactive Member


Message 4 of 52 (188993)
02-27-2005 6:17 PM
Reply to: Message 3 by pink sasquatch
02-27-2005 5:14 PM


Re: another, difficult assumption needed...
Great point. And let me restate that this exercise is just speculation - I'm not trying to 'prove' anything; just looking at Haldane's dilemma got me thinking and I thought playing around with a similar equation would help me better understand some things (certainly the complexity involved) about evolution from a more mathmatical point of view than I am used to seeing.
I was hoping someone could help devise some of these variables, as the one you pointed out, or to point to similar work others had done, in order to come up with some values that would fall within parameters that seem likely (yeah, subjective I know).
I was looking at some of the Haldane stuff where he calculates that it takes approx 300 generations for new genes to be 'fixed' in the population.
I'm sure this has been discussed here, and I was hoping for some help coming up with figures, or a range of figures, that people on this forum would feel comfortable with and see how the numbers play out.
The point of this is really just a sort of hands on learning exercise for me; and I thought this might be the best place to do it because perhaps some others will calloborate, or at least offer insight and criticism.
So back to your point, perhaps the 'frequency rate' I'm looking for is a combination between the number of generations it would take for new genes/mutations to 'stick' in the population AND the number of mutations necessary to create BCS type speciation (org A can't produce viable offspring with org B).
As you said, this could theoretically occur in a single generation, but is there a mean number/rate we could find acceptable that we could use in this equation?
Maybe it would be easier to stick with just one order, like Coleoptera (beetles). It's sufficiently large, I think, to get a sense of scale of the time involved.
Also, I'm not adverse to working backwards to develop some of these variables. Say using the oldest known Coleoptera fossil as a starting point for the timeline, and using 2005 as the end point.
Then extrapolating a 'mutation rate' and see how that compares to other orders?
This message has been edited by custard, 02-27-2005 18:31 AM

This message is a reply to:
 Message 3 by pink sasquatch, posted 02-27-2005 5:14 PM pink sasquatch has not replied

Replies to this message:
 Message 5 by NosyNed, posted 02-27-2005 6:26 PM custard has replied

  
custard
Inactive Member


Message 6 of 52 (189001)
02-27-2005 6:49 PM
Reply to: Message 5 by NosyNed
02-27-2005 6:26 PM


Re: Speciation events
ned writes:
I don't know pop. genetics or the math here but that strikes me as a nonsense number right off the top. It would seem to me that the time taken for fixation would depend on too many things for there to be any such single number. The population size is one obvious one, the degree that a change is selected for (how beneficial is it), how it relates to other genes and so on. It stikes me that no such single number would say anything meaningful at all. Perhaps a geneticist can help here.
Good points. And I'm certainly not trying to devise some sort of 'golden ratio' that I will apply to evolution and say "see! It does/doesn't work!"
I'm just trying to learn more about pop genetics and achieve a better understanding of what really needs to happen to achieve a level of biodiversity similar to what we see on earth today; because the explanation "evolution = mutation + NS + time" sounds great, but it is almost to the point of being a platitude.
Trying to comprehend exactly what COULD occur or what would HAVE to occur over 4 billion years without really digging into it, for me, is like trying to comprehend just 'how much' one million trillion dollars will buy. Sure it will buy a lot, but 'a lot' is still an abstraction at that point.
ned writes:
Another thing that might be true (but I'm guessing again) is the you don't have a "population" until you have a speciation event. Until that happens you have gene flow all over.
Great point. Obviously there is going to be a lot of guessing involved here. That's why I am soliciting your, and other folks' help, in making or reviewing some of my guesses.

This message is a reply to:
 Message 5 by NosyNed, posted 02-27-2005 6:26 PM NosyNed has replied

Replies to this message:
 Message 7 by NosyNed, posted 02-27-2005 7:01 PM custard has replied

  
custard
Inactive Member


Message 8 of 52 (189011)
02-27-2005 7:40 PM
Reply to: Message 7 by NosyNed
02-27-2005 7:01 PM


Re: Some numbers.
For starters, how many different individual multicellular (to keep the number only astronomical) organisms have lived on the planet in the last 600 million years?
Sure thing. You want fries with that?
Let me try this with beetles first. I'll post what I come up with and y'all can shoot it full of holes.
**side note: You know, if anything, this thread should be some indication to creationists of how much scrutiny scientists undergo when they present something to their peers. This is just an online forum, yet no one here is about to let me get away with anything - which is hardly a WHIFF of the type of scrutiny an actual scientist would get from his peers.**
This message has been edited by custard, 02-27-2005 19:40 AM

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 Message 9 by RAZD, posted 02-27-2005 8:29 PM custard has replied

  
custard
Inactive Member


Message 10 of 52 (189038)
02-27-2005 9:46 PM
Reply to: Message 9 by RAZD
02-27-2005 8:29 PM


Re: Some numbers.
RAZD writes:
if you can take a group where all (Z) species are known for the last (X) years and during that time there have been (Y) speciation events
then you can say for this group you get Y/X/Z speciation events per year per species
OK, here's what I came up with so far:
Using my Coleoptera example I found that the earliest known Coleoptera fossil was about 265 million years old.
Currently there are at least 350,000 species of Coleoptera.
Using the fecundity rate of the western corn rootworm beetle (for no other reason than it is convenient), the fecundity rate of my Coleoptera are, on average, 1 new generation per year.
Not accounting for extinction at this point the average number of new species that HAS to occur per year to reach 350K species is:
0.001320755 or ~ 1 new species every 757 years.
350,000 species/ 265 mil years
Now that I write this I already see two major problems:
1-Obviously there have been more than 350,000 Coleoptera species in the last 265 mil years, so to estimate the total number of Coleoptera I need to use a species extinction rate. I've decided to go with .01% extinctions/century as that falls within the estimated range of natural extinction rates .001% - 1% per century.
2- And this is where I am really blowing it I think, using my 1 generation/year fecundity rate after achieving my first speciation event 757 years in, won't I be dealing with two populations so now my fecundity rate is really 1 generation/year/species? Does that mean that I have a fecundity rate of 2 generations per year (one from pop A and one from pop A1)?
Freaking exponentials.
AS for RAZD's equation X = 265 million years. Z= 350,000. But I'm not sure what you mean be "speciation event." What is the difference between Z and Y?

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 Message 9 by RAZD, posted 02-27-2005 8:29 PM RAZD has replied

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 Message 13 by mick, posted 03-02-2005 4:09 PM custard has replied

  
custard
Inactive Member


Message 14 of 52 (189801)
03-03-2005 2:09 PM
Reply to: Message 13 by mick
03-02-2005 4:09 PM


Re: Some numbers.
Awesome. Thanks for the suggestion and the link Mick. I'll take a look.
You are absolutely right that some of the problems with my initial approach are that I've backed myself into a model where I'm using too many hypothetical variables.
RAZD suggested using a more restrictive model, say something that has been observed over 40 years, but to the best of my knowledge, there have been no observed speciation events that meet the criteria of the BSC (biological species concept):
quote:
"... that stage of evolutionary progress at which the once actually or potentially interbreeding array of forms becomes segregated into two or more separate arrays which are physiologically incapable of interbreeding."
And, frankly, I'm starting to wonder where the evidence for this type of speciation can be found. Looking at wolf-like canids alone I have to ask WHY haven't we seen this type of speciation (BSC) despite evidence that humans have segregated canid sub-species populations and bred them selectively for what, 10,000 years or so?
Yet wolves, coyotes, and pugs can still interbreed and produce viable offspring. The typical evo argument "well enough time hasn't passed" is starting to ring hollow. How much time is 'enough time?'
What is the minimum number of generations necessary for BSC speciation? 100,000? 10 million?
It's not that I doubt evolution occurs, we certainly went from populations of single celled organisms to our current state of biodiversity, but I'm really beginning to question HOW it occurs; specifically, the common explanations of how it occurs which I encounter in this forum daily. These explanations are beginning to seem simplistic to me and smack of ignorance of the actual process, and, yes, even 'faith' in a process that isn't nearly as well understood as one would think reading some of these threads.

This message is a reply to:
 Message 13 by mick, posted 03-02-2005 4:09 PM mick has replied

Replies to this message:
 Message 15 by Loudmouth, posted 03-03-2005 2:32 PM custard has replied
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custard
Inactive Member


Message 17 of 52 (189818)
03-03-2005 3:13 PM
Reply to: Message 15 by Loudmouth
03-03-2005 2:32 PM


Re: Some numbers.
loudmouth writes:
However, we can't predict long term patterns with any specificity because the forces in motion are not amenable to modeling. It comes down to the randomness of mutations, the randomness of environmental changes, and the inherent chaos that our universe is in. Explanations are simplistic because the specifics are always different. The effects of speciation are consistent, but the causes of speciation are always complicated and inconsistent.
This is a good answer, yet I still hear you saying "we know that evolution occurs, but we can't actually predict when it will occur, how it will occur, why it doesn't occur when, where, or how we expect it to, etc."
You can see how some might find that explanation eerily similar to creation arguments about why god designed things this way or that way, don't you?
Even with our limited knowledge of climatology we have enough data to make predictions that bear out. I think it is reasonable to expect us to come up with reasonable parameters about how long it SHOULD take to achieve speciation.
Any model hits the old wall of "the map is not the territory". Every model is going to be insufficient, at least in my opinion. I think it is a topic worthy of consideration and debate, but in the end I think it will be a Fool's Errand.
I'm getting sick of that map phrase (no offense - but I swear I've read it about fifty times in the last week or so), and ultimately it smacks of a bit of a cop out. Sometimes a simple "we just don't know" is the most honest and accurate answer. Platitudes are rarely satisfying - how many religious platitudes do evos find solace in?
I read "the map is not the territory" and I hear "that's just the will of god" echoing in my head.
Folly to attempt simple speciation models? Probably. Yet in pursuing this folly I hope to at least get a better understanding of things. Yet in this type of foolishness, I find myself in good company: the scientists and thinkers who look for impossible answers to impossible questions.

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 Message 15 by Loudmouth, posted 03-03-2005 2:32 PM Loudmouth has replied

Replies to this message:
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custard
Inactive Member


Message 18 of 52 (189823)
03-03-2005 3:47 PM
Reply to: Message 16 by pink sasquatch
03-03-2005 2:59 PM


Chihuahua + Saint Bernard = ?
pink writes:
But Saint Bernards and Chihuahuas cannot. (And I'm not entirely sure that a wolf and a pug could successfully reproduce.)
Cannot? Or do not? If you inseminated a Saint Bernard bitch with Chihuahua semen no viable offspring would be produced?

This message is a reply to:
 Message 16 by pink sasquatch, posted 03-03-2005 2:59 PM pink sasquatch has replied

Replies to this message:
 Message 19 by pink sasquatch, posted 03-03-2005 3:56 PM custard has replied

  
custard
Inactive Member


Message 22 of 52 (189830)
03-03-2005 4:02 PM
Reply to: Message 16 by pink sasquatch
03-03-2005 2:59 PM


Re: hormonal butterflies
pink writes:
One, basically. A single mutation can result in reproductively incompatibility.
Hypothetically, sure. How many biologists are willing to walk that narrow, swaying limb and say that this actually DOES occur. Plus, you still have to have a population of your new species. One reproductive anamoly does not a species make.
(Ah, I see you make that point here:
Now, these mutations/reproductive incompatibilites arise in a single generation, but it may take several generations for fixation into separate populations.
I'm more interested in 'what is likely' vs what is theoretically possible. Haldane took a stab at it, but seemed to get more criticism than anything else. I'm having difficulty finding similar research.
Another example of premating isolation as the result of a single mutation was witnessed by researchers in a population of snails - snails with the mutation had the opposite shell
Ahh the snails. This doesn't seem to meet the criteria I established in the OP - using the BSC definition of speciation, which would include artificial insemination.
I know the BSC is restrictive, but I think it is the clearest way to show non-evolutionists that speciation, not hybridization and the odd mutation - actually occurs.
In any case, I don't think the snails are a good example. As Wounded King pointed out (I'll look for the post) they could still reproduce through artificial insemination. An analogy would be a man who has a low sperm count (genetic) and can't produce viable offspring with his wife without artificial means. Is he really a member of a different species?
[qspink]An example of postmating speciation that comes to mind is the Robertsonian chromosomal fusions in wild mice (I believe a substantial body of work has been done characterizing these reproductively isolated populations in the Alps). [/qs]
Cool. I'll check this out. This could be exactly what I am looking for.
As always, you provide good food for thought.

This message is a reply to:
 Message 16 by pink sasquatch, posted 03-03-2005 2:59 PM pink sasquatch has replied

Replies to this message:
 Message 24 by pink sasquatch, posted 03-03-2005 4:22 PM custard has replied

  
custard
Inactive Member


Message 23 of 52 (189832)
03-03-2005 4:11 PM
Reply to: Message 21 by Loudmouth
03-03-2005 3:58 PM


Re: Some numbers.
loudmouth writes:
For instance, no one can predict the temperature in NY city for December 21, 2015. Does that mean that we don't understand the mechanisms of climatology? Of course not. What SHOULD the temperature be on December 21, 2015? At best, between -100 and 100 degrees F.
Great point. I would add that we know enough about climatology to predict the weather parameter for 2015 will be much narrower than that barring some superdupernino event.
And that's what I'm looking for with are current knowledge of how evolution works - or how we THINK it works. How valid, or useful, is a theory that says "well a new species may or may not evolve in the next twenty thousand years." Crap, present that model to the Kansas School Board and ID will be part of the curriculum faster than boiled asparagus.
We have lots and lots of information about evolution, I'm sure there have to be models out there that have been devised, or are being devised, that provide more insight into the frequency and likelihood of evolution than the weather in NY analogy. At least I hope so.
loudmouth writes:
The voices in your head sound a lot more entertaining than mine do though.
That reminds me, I need to up my lithium dosage...

This message is a reply to:
 Message 21 by Loudmouth, posted 03-03-2005 3:58 PM Loudmouth has replied

Replies to this message:
 Message 25 by Loudmouth, posted 03-03-2005 4:23 PM custard has replied
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custard
Inactive Member


Message 26 of 52 (189840)
03-03-2005 4:25 PM
Reply to: Message 19 by pink sasquatch
03-03-2005 3:56 PM


Re: Chihuahua + Saint Bernard = St. Hua! Hua!
pink writes:
If the only way two populations can/will reproduce is by human transfer of semen, then those two populations are not the same species by the BSC definition.
OK, I see where I'm miscommunicating. I think.
(Using the talkorgins defintions) the BSC definition I'm using, which I think I stated in the OP, is:
"... that stage of evolutionary progress at which the once actually or potentially interbreeding array of forms becomes segregated into two or more separate arrays which are physiologically incapable of interbreeding." (Dobzhansky 1937)
It is important to note that this is a highly restrictive definition of species. It emphasizes experimental approaches and ignores what goes on in nature.
Yes, Dobzhansky modified his definition in 1942:
He defined species as
"... groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups."
The examples you've provided to meet the latter criteria, but that is not restrictive enough for me in this thread. I'm aware of the examples of speciation cited that meet looser criteria, but I don't think the stricter definition is at all unreasonable to use when one considers that evolution accounts for speciation from single celled organisms to multi-cellular plant and animal life.

This message is a reply to:
 Message 19 by pink sasquatch, posted 03-03-2005 3:56 PM pink sasquatch has replied

Replies to this message:
 Message 29 by pink sasquatch, posted 03-03-2005 4:33 PM custard has replied

  
custard
Inactive Member


Message 28 of 52 (189844)
03-03-2005 4:31 PM
Reply to: Message 25 by Loudmouth
03-03-2005 4:23 PM


Re: Some numbers.
loudmouth writes:
Natural selection also pushes species in two directions, one force pushes species towards stability while the other force pushes towards change. To trot out another worn phrase, future speciation is being controlled by the Butterfly Effect. One small change early in the process could have large ramifications further down the pipeline.
I think this concept doesn't get much play with creos (or some of the evos even) here. This makes me think that a variable (for a much grander model than what I'm futzing about with) would be some sort population plateau where the sheer number of an existing species would prevent continued evolution because any and all new mutations are eventually cycled back into the population at large; then the mutations are simply watered down and exist in isolated pockets, or just die out.
Once the species reaches a certain level, it would become extremely resistant to additional speciation because the baseline genes (for lack of a better phrase) would keep the overall species characteristics near the mean.
I think this would be a sort of punctuated equilibrium argument, no?

This message is a reply to:
 Message 25 by Loudmouth, posted 03-03-2005 4:23 PM Loudmouth has replied

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custard
Inactive Member


Message 30 of 52 (189846)
03-03-2005 4:42 PM
Reply to: Message 27 by pink sasquatch
03-03-2005 4:30 PM


Re: 20,000?
Neither description of the BSC includes human intervention as an exception.
Do you honestly believe a Saint Bernard and a Chihuahua are seperate species simply because their reproductive organs don't fit together?
You just can't rule out genetics and rely solely on morphology. Our current taxonomy overemphasized morphology and needs to be re-evaluated with more emphasis on genetics.
Similarly, speciation solely as a result of geographic isolation is also incredibly weak. Europeans didn't encounter Australian aborigines until thousands of years later. Are caucasians and aborigines truly a seperate species?

This message is a reply to:
 Message 27 by pink sasquatch, posted 03-03-2005 4:30 PM pink sasquatch has replied

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custard
Inactive Member


Message 31 of 52 (189848)
03-03-2005 4:45 PM
Reply to: Message 29 by pink sasquatch
03-03-2005 4:33 PM


quote mine? Please.
Your definition is NOT the one promoted by TalkOrigins, rather it is a quote-mine, mistaken or not.
.
It would be a quote mine only if I were misreprenting the quote. Look back at the OP, I clearly stated I wanted to use a very restrictive definition of BSC.
If you like I'll REVISE it to say the "1937 Dobzhansky definition of BSC."
Regardless, this is the definition I stated that I am using and I have explained why I'm using it. I am NOT arguing that more liberal definitions of the BSC are incorrect.

This message is a reply to:
 Message 29 by pink sasquatch, posted 03-03-2005 4:33 PM pink sasquatch has replied

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custard
Inactive Member


Message 32 of 52 (189850)
03-03-2005 4:55 PM
Reply to: Message 24 by pink sasquatch
03-03-2005 4:22 PM


Re: not my BSC
custard writes:
One reproductive anamoly does not a species make.
Pink responds:
Why yes, yes it does. That's all biological speciation is - reproductive incompatibility.
So Joe Lowspermcount is a separate species from homo sapiens because he is unable to reproduce? Are you really saying that?
Doesn't genetic similarity come into play at some point?
This message has been edited by custard, 03-03-2005 16:55 AM

This message is a reply to:
 Message 24 by pink sasquatch, posted 03-03-2005 4:22 PM pink sasquatch has replied

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