Register | Sign In


Understanding through Discussion


EvC Forum active members: 57 (9175 total)
2 online now:
Newest Member: Neptune7
Post Volume: Total: 917,628 Year: 4,885/9,624 Month: 233/427 Week: 43/103 Day: 1/11 Hour: 0/1


Thread  Details

Email This Thread
Newer Topic | Older Topic
  
Author Topic:   Galapagos finches
Tamara
Inactive Member


Message 1 of 104 (84189)
02-07-2004 10:05 AM


I've been reading Milton, and some of what he says about the finches makes sense to me. Wanted to run that by y'all.
He says that the finches fluctuate in beak size over wet and dry seasons, with little net change. That they interbreed, producing vigorous offspring. And that division into thirteen species may be wishful thinking.
Now I am not questioning that they demonstrate natural selection in action. I am questioning speciation here. It seems to me that when the definition of speciation in higher animals was diluted from Dobzhansky's original spec (cannot physiologically interbreed with other groups) then the door was opened for cheating.
Can it be argued that the Galapagos finch is one species with regional variations, and that it shows nothing whatsoever about macroevolution?
I mean, humans vary far more than the finches, and we are still one species....

Replies to this message:
 Message 2 by PaulK, posted 02-07-2004 6:11 PM Tamara has not replied

  
PaulK
Member
Posts: 17838
Joined: 01-10-2003
Member Rating: 3.8


Message 2 of 104 (84334)
02-07-2004 6:11 PM
Reply to: Message 1 by Tamara
02-07-2004 10:05 AM


Have you any objective measure of how different the finches are ? The variations in humans seem obvious to us but genetically we really are't that different.
Drawing a fine line between sub-species and species is not possible and there are always arguments (which is to be expected given that new species do form by evolution), however I do not think that there is any reasonable chance that the "finches" represent a single species.

This message is a reply to:
 Message 1 by Tamara, posted 02-07-2004 10:05 AM Tamara has not replied

  
Tamara
Inactive Member


Message 3 of 104 (84443)
02-08-2004 10:01 AM


Wells says:
Writing in Science in 1992, the Grants [finch researchers of good and long repute living on the islands] noted that the superior fitness of hybrids among populations of Darwin's finches "calls into question their designation as species." The following year, Peter Grant acknowledged that if species were strictly defined by inability to interbreed then "we would recognize only two species of Darwin's finch on Daphne," instead of the usual four. "The three populations of ground finches on Genovesa would similarly reduced to one species." Grant continued. "At the extreme, six species would be recognized in place of the current 14, and additional study might necessitate yet further reduction."
Peter R Grant and B. Rosemary Grant, "Speciation and hybridization in island birds", Phil. Trans. of the Royal Soc. of London B 351 (1996), pp765-772.
Also, P Grant, Ecology and Evolution of Darwin's Finches, p206.
Also, Grants' article in Endless Forms (Howard and Berlocher eds 1998), pp 404-422.

Replies to this message:
 Message 4 by PaulK, posted 02-08-2004 10:10 AM Tamara has not replied
 Message 5 by Coragyps, posted 02-08-2004 10:45 AM Tamara has not replied

  
PaulK
Member
Posts: 17838
Joined: 01-10-2003
Member Rating: 3.8


Message 4 of 104 (84444)
02-08-2004 10:10 AM
Reply to: Message 3 by Tamara
02-08-2004 10:01 AM


Well Wells is not exactly trustworthy but even if he is correct here, six is still significantly greater than one.
This essay comments on Wells claims about the Galapagos finches
Jonathan Wells and Darwin's Finches

This message is a reply to:
 Message 3 by Tamara, posted 02-08-2004 10:01 AM Tamara has not replied

  
Coragyps
Member (Idle past 819 days)
Posts: 5553
From: Snyder, Texas, USA
Joined: 11-12-2002


Message 5 of 104 (84448)
02-08-2004 10:45 AM
Reply to: Message 3 by Tamara
02-08-2004 10:01 AM


I think the Grants' work just reinforces the concept that ol' Mother Nature is a lot messier than we humans would like her to be - we want a species to be a single thing that we can hold the archetype for in our hand, and reality just isn't that way. Johnathan Weiner's The Beak of the Finch is a pretty readable summary of the Grants' studies, BTW.

This message is a reply to:
 Message 3 by Tamara, posted 02-08-2004 10:01 AM Tamara has not replied

  
Tamara
Inactive Member


Message 6 of 104 (84495)
02-08-2004 2:51 PM


The above linked article says: But wait a minute. Are species defined "strictly by inability to interbreed"? Not by any species concept commonly used today. The Biological Species concept as described by Mayr emphasizes reproductive isolation rather than lack of interfertility. The key to the concept is barriers to gene exchange, which can include infertility, but are not restricted to it by any means. Discussions of prezygotic reproductive barriers can be found in any decent textbook. Wells knows this. He also knows that reproductive isolation in the finches on the Galapagos is primarily of the prezygotic type, because his sources by the Grants emphasize it over and over. So, Wells has no real point here. However, the general public not familiar with species concepts as used by biologists might consider his arguments authoritative.
Well, no, not so fast. Species was defined by Dobzhansky as based on the physiological inability to interbreed, originally. This concept has been moved away from, the literature says, because it creates problems in plants and asexual organisms. It is also impossible to apply to fossils. However, when it comes to higher animals of the still existing category, it has the advantage of preventing wishful thinking of the kind that may well have happened with the finches, where we have a bunch of birds that are almost identical, with some differences in beaks, songs, and the food they eat, among whom preferences for mating with their own in-group has been noted, but has not been exclusive. If this kind of thinking were to be applied to humans, the Chassids would be a separate species!
The concept of a species is not a clean one and never will be. However, since the key issue about the theory of evolution is accounting for how one organism can evolve into another PROFOUNDLY DIFFERENT organism, I think biology should be careful about not trivializing the concept of species.
For more info on speciation: Observed Instances of Speciation
Yes, six is more than one, but please note Grant thinks that further reduction could well come with further reevaluation.
[This message has been edited by Tamara, 02-08-2004]
[This message has been edited by Tamara, 02-08-2004]

Replies to this message:
 Message 7 by PaulK, posted 02-08-2004 3:11 PM Tamara has not replied

  
PaulK
Member
Posts: 17838
Joined: 01-10-2003
Member Rating: 3.8


Message 7 of 104 (84498)
02-08-2004 3:11 PM
Reply to: Message 6 by Tamara
02-08-2004 2:51 PM


Let us be clear. According to the quote Grant thinks that six is the minimum based on the current data and only that new data *might* reduce the number further. So the idea that there's just one species is a pretty much a non-starter.
And why do you say that biology is "trivialising" the concept of species ? The definition is being adjusted to try and deal with the very real problems of taxonomy because we don't have clear boundaries - as evolution predicts.
[This message has been edited by PaulK, 02-08-2004]

This message is a reply to:
 Message 6 by Tamara, posted 02-08-2004 2:51 PM Tamara has not replied

  
Tamara
Inactive Member


Message 8 of 104 (84501)
02-08-2004 3:29 PM


An interesting perspective on the species issue could come from Dawkins' formula which calls a species a group that has the same number of chromosomes as well as the same number of nucleotides on each. I have read that the finches all have the same number of chromosomes but have not seen any info on the nucleotides. Anyone?
Re trivializing, Paul, see my argument ad absurdum (Chassids, above). People should not be calling any group a species just because it has a few different characteristics. Btw, I just heard that wolves, coyotes and dogs have been combined into one species, Canis lupus, with appropriate subspecies. About time! Jackals, however, still roam at large as a separate species.

Replies to this message:
 Message 9 by PaulK, posted 02-08-2004 3:51 PM Tamara has not replied
 Message 11 by Trixie, posted 02-08-2004 4:36 PM Tamara has not replied

  
PaulK
Member
Posts: 17838
Joined: 01-10-2003
Member Rating: 3.8


Message 9 of 104 (84506)
02-08-2004 3:51 PM
Reply to: Message 8 by Tamara
02-08-2004 3:29 PM


Well if you really think that small birds have the intelligence to set up inward-looking communities on the same basis as the Chassids then you might have a point.
But lack of interfertility isn't even appropriate to asexually reproducing species - and that includes at least one vertebrate species (whiptail lizards).
On the other heand we have so-called "cryptic" species which are almost impossible to distinguish by their physical forms, yet do not interbreed.
I hadn't heard that coyotes had been classified as the same species as wolves - but it wouldn't surprise me. Taxonomy is a constant battle between "lumpers" and "splitters".
Then there are other species concepts, such as the ecological species concept or the recognition species concept.
No single species concept actually works perfectly.

This message is a reply to:
 Message 8 by Tamara, posted 02-08-2004 3:29 PM Tamara has not replied

  
Tamara
Inactive Member


Message 10 of 104 (84513)
02-08-2004 4:23 PM


True. But unless we come up with something that works for birds in such a way that wishful thinking does not play a major role, the Galapages finches remain an illustration for natural selection or even adaptive radiation. But as an illustration of speciation they are not credible, IMO.
A quote from the Beak of the Finch: "You can't distinguish these three species by their plumage and usually not by their build or body size either. You have to tell them apart by their beaks. In the jargon of taxonomy, the sullen art of classification, the beak of the ground finch is diagnostic: it is the bird's chief taxonomic character. But because the finches and their beaks are so variable, many of them "are so intermediate in appearance that they cannot safely be identified-a truly remarkable state of affairs. . . ."

Replies to this message:
 Message 12 by PaulK, posted 02-08-2004 4:47 PM Tamara has not replied

  
Trixie
Member (Idle past 3790 days)
Posts: 1011
From: Edinburgh
Joined: 01-03-2004


Message 11 of 104 (84515)
02-08-2004 4:36 PM
Reply to: Message 8 by Tamara
02-08-2004 3:29 PM


Same number of nucleotides??
I wouldn't be too pleased if they started to define a species as individuals having the same number of chromosomes and the same number of nucleotides for the simple reason that you find human individuals with a deleted segment in comparison to their parents, or maybe a different number of trinucleotide repeats. Are we to start dividing up the entire human population based on the number of nucleotides they have on each chromosome?

This message is a reply to:
 Message 8 by Tamara, posted 02-08-2004 3:29 PM Tamara has not replied

  
PaulK
Member
Posts: 17838
Joined: 01-10-2003
Member Rating: 3.8


Message 12 of 104 (84517)
02-08-2004 4:47 PM
Reply to: Message 10 by Tamara
02-08-2004 4:23 PM


Unless the evidence actually indicates that the "finches" are best classified as a single species - and so far there is only a chance that the number could be finally reduced to less than six, which is the lowest number suggested by the most recent data we do have there's a very good case that we do have a genuine example of speciation here.
And it is hardly the only example we have.

This message is a reply to:
 Message 10 by Tamara, posted 02-08-2004 4:23 PM Tamara has not replied

  
Tamara
Inactive Member


Message 13 of 104 (84518)
02-08-2004 5:10 PM


Trixie, thanks for the feedback. I guess Dawkins's suggestion does not make sense after all...
quote:
And it is hardly the only example we have.
That's a good thing, then, because this one is skating on thin ice. Maybe we should ask the Grants what they think about this...
You talk about evidence, Paul. I have been looking for evidence that the historical classification is on solid footing. I have not found it. So far. If anyone here has it, I'll be happy to look at it.
[This message has been edited by Tamara, 02-08-2004]

Replies to this message:
 Message 14 by PaulK, posted 02-08-2004 5:50 PM Tamara has not replied
 Message 15 by MrHambre, posted 02-08-2004 9:24 PM Tamara has not replied

  
PaulK
Member
Posts: 17838
Joined: 01-10-2003
Member Rating: 3.8


Message 14 of 104 (84523)
02-08-2004 5:50 PM
Reply to: Message 13 by Tamara
02-08-2004 5:10 PM


In case you haven't noticed I haven't been disagreeing with the Grants at all. You're the one who wants to jump to there only being one species, and that isn't supported at all.

This message is a reply to:
 Message 13 by Tamara, posted 02-08-2004 5:10 PM Tamara has not replied

  
MrHambre
Member (Idle past 1477 days)
Posts: 1495
From: Framingham, MA, USA
Joined: 06-23-2003


Message 15 of 104 (84567)
02-08-2004 9:24 PM
Reply to: Message 13 by Tamara
02-08-2004 5:10 PM


Beaks Are For Evolving
I like how creationists still act surprised to learn that it's considerably difficult to determine when a new species has emerged. In Darwinian terms, a species is just convenient shorthand that stands in for a distinction that only a creationist thinks should be straightforward. Creationism, as far as anyone can tell, alleges that certain forms of life may share ancestry, only no one's been able to determine how much. The theory of common descent asserts that all life shares ancestry, so all differences are matters of degree and never of essence.
The Galapagos finches are fascinating for the fact that they show how a formerly unified population has exploited separate niches and developed structures and instincts best suited to their individual environments. The effect of geographical distribution on the rate of speciation is dramatic and persuasive to any rational observer. Unfortunately, creationists have a vested interest in denying that speciation events take place, and for that reason only, they can't consider the finches separate species.
Regardless of the designation of species or subspecies, it's quite obvious that evolution by natural selection has been responsible for a significant amount of observable variation in descendants of fairly recent common ancestors. Creationists never tire of telling us that the Galapagos finches tell us nothing about the mechanisms of evolution, that this isn't Darwinian evolution at all, and that we should ignore the clear lessons these birds teach us about the development of life on Earth.

The dark nursery of evolution is very dark indeed.
Brad McFall

This message is a reply to:
 Message 13 by Tamara, posted 02-08-2004 5:10 PM Tamara has not replied

  
Newer Topic | Older Topic
Jump to:


Copyright 2001-2023 by EvC Forum, All Rights Reserved

™ Version 4.2
Innovative software from Qwixotic © 2024