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Author Topic:   All species are transitional
robinrohan
Inactive Member


Message 166 of 246 (255171)
10-27-2005 4:40 PM
Reply to: Message 163 by mick
10-27-2005 3:04 PM


Re: From Lightly to Heavily speckled
I agree that it seems unlikely that there are whole bunch of genes that control the amount of speckling on an animal's coat. But that isn't really the way that the speckling is being specified. The amount of speckling will likely be determined by some threshold mechanism that operates during development; Perhaps there is a hormone or something that causes pigmentation to develop when it reaches a local threshold, and this hormone is in a feedback loop with an inhibitor such that if one part of the skin is high in concentration of the hormone, it's neighbours will be low. Slight changes to the threshold level of the hormone's activity and slight changes to the decay rate, the feedback mechanism, etc. might well produce a huge variety of different specklinesses, from spots to stripes, dots, cheetah spots, etc. etc.

So what you are saying is that more mutations are not necessarily required? That's what I want to know.


"Turning out pigs for creationists makes me blue and blurry."--Brad McFall
This message is a reply to:
 Message 163 by mick, posted 10-27-2005 3:04 PM mick has responded

Replies to this message:
 Message 188 by mick, posted 10-28-2005 1:06 PM robinrohan has responded

  
robinrohan
Inactive Member


Message 167 of 246 (255174)
10-27-2005 4:50 PM
Reply to: Message 165 by crashfrog
10-27-2005 3:59 PM


Re: speckles
I don't understand how you could. It's self-evident to me that gene flow exists between a parent and its offspring; thus, no reproductive isolation.

You're right. I misstated it.


This message is a reply to:
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robinrohan
Inactive Member


Message 168 of 246 (255176)
10-27-2005 5:18 PM
Reply to: Message 160 by RAZD
10-27-2005 7:42 AM


Re: speckles
Final divergence is achieved when NS disappears due to sexual selection of NN for only NN {AND?\OR?} of SS for only SS.

Let's say this happened.

We had semi-isolation, as you described, for a while, and then "final divergence" occurred. Could we pin that event down to a particular date? What does final divergence consist of? I guess we could say that when the last lightly speckled creature died, at that moment in time--100 hundred million years ago, give or take a few days--we suddenly had 2 distinct species--heavily speckled Eutherians and black, unspeckled Eutherians. That's according to the definition of "gene pool isolation."

Seems like a quite definite moment in time to me.


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 Message 169 by Percy, posted 10-27-2005 5:37 PM robinrohan has responded

  
Percy
Member
Posts: 18309
From: New Hampshire
Joined: 12-23-2000
Member Rating: 2.7


Message 169 of 246 (255178)
10-27-2005 5:37 PM
Reply to: Message 168 by robinrohan
10-27-2005 5:18 PM


Species Transition Point
When does bay become ocean? When do foothills become mountains? When does a boy become a man?

As the genetic similarity between two populations declines from 100% to 99.9999% to 99.9998% and so forth, at what point should the two populations be deemed separate species?

These are rhetorical questions. Any chosen dividing line is arbitrary.

--Percy


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 Message 168 by robinrohan, posted 10-27-2005 5:18 PM robinrohan has responded

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robinrohan
Inactive Member


Message 170 of 246 (255180)
10-27-2005 5:47 PM
Reply to: Message 169 by Percy
10-27-2005 5:37 PM


Re: Species Transition Point
As the genetic similarity between two populations declines from 100% to 99.9999% to 99.9998% and so forth, at what point should the two populations be deemed separate species?

The moment they are totally isolated. What's arbitrary about that?


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Replies to this message:
 Message 171 by crashfrog, posted 10-27-2005 7:10 PM robinrohan has not yet responded
 Message 172 by NosyNed, posted 10-27-2005 7:13 PM robinrohan has responded
 Message 173 by RAZD, posted 10-27-2005 7:14 PM robinrohan has responded

  
crashfrog
Inactive Member


Message 171 of 246 (255203)
10-27-2005 7:10 PM
Reply to: Message 170 by robinrohan
10-27-2005 5:47 PM


Re: Species Transition Point
The moment they are totally isolated. What's arbitrary about that?

The moment that they are "totally isolated" is completely arbitrary. That's what's arbitrary about it - it's arbitrariness.


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NosyNed
Member
Posts: 8838
From: Canada
Joined: 04-04-2003


Message 172 of 246 (255204)
10-27-2005 7:13 PM
Reply to: Message 170 by robinrohan
10-27-2005 5:47 PM


Totally Isolated
In the contrived example we are discussing the isolation becomes complete when the mixed population dies away. So if you take this as the "speciation" you're saying that the heavy speckles are not a species at one moment and then when something over the nearby hill gets swallowed by a boa it suddenly becomes a species.

That may be correct in some way, but it is a bit odd.


This message is a reply to:
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RAZD
Member
Posts: 19756
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 5.5


Message 173 of 246 (255205)
10-27-2005 7:14 PM
Reply to: Message 170 by robinrohan
10-27-2005 5:47 PM


Re: Species Transition Point
But can you guarantee that sexual isolation remains a dividing factor?

Perhaps if a survival stress were applied to the area where the asian green warbler ring species overlaps that there would exist individuals that would interbreed even after having been sexually isolated.

You could have transition back and forth.


we are limited in our ability to understand
by our ability to understand

RebelAAmerican.Zen[Deist
... to learn ... to think ... to live ... to laugh ...
to share.


This message is a reply to:
 Message 170 by robinrohan, posted 10-27-2005 5:47 PM robinrohan has responded

Replies to this message:
 Message 175 by robinrohan, posted 10-27-2005 7:57 PM RAZD has responded

  
robinrohan
Inactive Member


Message 174 of 246 (255209)
10-27-2005 7:55 PM
Reply to: Message 172 by NosyNed
10-27-2005 7:13 PM


Re: Totally Isolated
So if you take this as the "speciation" you're saying that the heavy speckles are not a species at one moment and then when something over the nearby hill gets swallowed by a boa it suddenly becomes a species.
That may be correct in some way, but it is a bit odd.

That's it exactly. While the lightly speckled Eutherian was still alive, there was the possibility of gene flow between the two other groups, since the lightly speckled one could mate with both groups, but the other two groups couldn't mate with each other, as you and RAZD explained. The moment that lightly speckled one died, there was total isolation.

This is why I have a problem with that particular definition of "species"--it's not arbitrary, by which I mean it's not a matter of just labelling something a different species out of convenience.

However, if we adopt another definition--physical changes--the labelling is arbitrary. The only difference between the 2 groups is that one is speckled and one isn't. Otherwise they are identical. One could call them variants using the other definition. But you can't do that with "gene pool isolation."

This lack of arbitrariness matters if the various analogies about seemlessness are going to work (color spectrums, etc.)

This message has been edited by robinrohan, 10-27-2005 07:02 PM


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robinrohan
Inactive Member


Message 175 of 246 (255211)
10-27-2005 7:57 PM
Reply to: Message 173 by RAZD
10-27-2005 7:14 PM


Re: Species Transition Point
Perhaps if a survival stress were applied to the area where the asian green warbler ring species overlaps that there would exist individuals that would interbreed even after having been sexually isolated.

I'm not sure what you are referring to here.


This message is a reply to:
 Message 173 by RAZD, posted 10-27-2005 7:14 PM RAZD has responded

Replies to this message:
 Message 176 by RAZD, posted 10-27-2005 8:06 PM robinrohan has responded

  
RAZD
Member
Posts: 19756
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 5.5


Message 176 of 246 (255215)
10-27-2005 8:06 PM
Reply to: Message 175 by robinrohan
10-27-2005 7:57 PM


Re: Species Transition Point
The sexual selection barrier may apply when the living is easy, but when times get tough the selection of mates may be less picky when survival is at stake.

This was observed on the Galapagos Islands when two finch species interbred during a drought that did not interbreed before or after the drought.

Line ... no line ... line ... :rolleyes:


we are limited in our ability to understand
by our ability to understand

RebelAAmerican.Zen[Deist
... to learn ... to think ... to live ... to laugh ...
to share.


This message is a reply to:
 Message 175 by robinrohan, posted 10-27-2005 7:57 PM robinrohan has responded

Replies to this message:
 Message 177 by robinrohan, posted 10-27-2005 8:35 PM RAZD has responded
 Message 178 by Nighttrain, posted 10-27-2005 8:41 PM RAZD has responded

  
robinrohan
Inactive Member


Message 177 of 246 (255222)
10-27-2005 8:35 PM
Reply to: Message 176 by RAZD
10-27-2005 8:06 PM


Re: Species Transition Point
This was observed on the Galapagos Islands when two finch species interbred during a drought that did not interbreed before or after the drought.

Any way to know why they didn't interbreed before that?


This message is a reply to:
 Message 176 by RAZD, posted 10-27-2005 8:06 PM RAZD has responded

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Nighttrain
Member (Idle past 2071 days)
Posts: 1512
From: brisbane,australia
Joined: 06-08-2004


Message 178 of 246 (255223)
10-27-2005 8:41 PM
Reply to: Message 176 by RAZD
10-27-2005 8:06 PM


Re: Species Transition Point
The sexual selection barrier may apply when the living is easy, but when times get tough the selection of mates may be less picky when survival is at stake.
This was observed on the Galapagos Islands when two finch species interbred during a drought that did not interbreed before or after the drought.

So the blocking mechanism preventing mating between different species, barring environmental factors, is tied in with physical appearance or a surface level. As against a block on the cell level where different species may mate but produce no viable issue?

Wish I could explain that to my neighbour`s Dalmatian who repeatedly humps a concrete statue of Venus deMilo in his garden. :D


This message is a reply to:
 Message 176 by RAZD, posted 10-27-2005 8:06 PM RAZD has responded

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RAZD
Member
Posts: 19756
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 5.5


Message 179 of 246 (255232)
10-27-2005 9:27 PM
Reply to: Message 178 by Nighttrain
10-27-2005 8:41 PM


Re: Species Transition Point
Wish I could explain that to my neighbour`s Dalmatian ...

What you are seeing is (usually male) sexual behavior with object less and less similar to potential mates due to a lack of better opportunities. This is one of the driving forces for the trend to regress species diversity in times of survival stress.

Or it is in love with an image of the master. :laugh:


we are limited in our ability to understand
by our ability to understand

RebelAAmerican.Zen[Deist
... to learn ... to think ... to live ... to laugh ...
to share.


This message is a reply to:
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RAZD
Member
Posts: 19756
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 5.5


Message 180 of 246 (255233)
10-27-2005 9:30 PM
Reply to: Message 177 by robinrohan
10-27-2005 8:35 PM


Re: Species Transition Point
Any way to know why they didn't interbreed before that?

General lack of opportunity coupled with plentiful normal opportunity would by my assumption. When species are in survival stress they tend to move outside native territories looking for ones more like what they knew before, and this puts them into a position of more interaction with other species. On the Galapagos we have descrete islands so it is easy to focus on when the barriers are crossed.


we are limited in our ability to understand
by our ability to understand

RebelAAmerican.Zen[Deist
... to learn ... to think ... to live ... to laugh ...
to share.


This message is a reply to:
 Message 177 by robinrohan, posted 10-27-2005 8:35 PM robinrohan has not yet responded

  
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