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Author Topic:   Isolation---by distance as well as barriers?
InGodITrust
Member (Idle past 1669 days)
Posts: 53
From: Reno, Nevada, USA
Joined: 05-02-2009


Message 1 of 16 (511667)
06-11-2009 4:07 AM


Hi Folks. Help me understand Darwin when he wrote that two or more varieties could be formed in a strictly continuous area. He also wrote he believed "many perfectly defined species have been formed on strictly continuous areas".
Isn't isolation neccesary for evolution? So if there are no geographical barriers to separate different groups of a species, can mere distance serve to isolate them?
Hypothetically, I'm thinking of a species of hare that has a range...let's say 300 miles wide. Wouldn't the genes of all the would-be varieties keep criss-crossing across the range, and keep the species pure? Or if the distance is great enough, can varieties form?
Thanks for any help.

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Adminnemooseus
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Message 2 of 16 (511670)
06-11-2009 4:35 AM


Thread moved here from the Proposed New Topics forum.

  
Dr Adequate
Member (Idle past 284 days)
Posts: 16113
Joined: 07-20-2006


Message 3 of 16 (511673)
06-11-2009 5:07 AM
Reply to: Message 1 by InGodITrust
06-11-2009 4:07 AM


Hypothetically, I'm thinking of a species of hare that has a range...let's say 300 miles wide. Wouldn't the genes of all the would-be varieties keep criss-crossing across the range ...
Consider a species of hare with a variety that lives above the snowline and a variety that lives below, each adapted to their environments, and suppose them capable of interbreeding. Nonetheless, it might be the case that any cross between the two varieties would be inferior to the below-the-snowline variety in living below the snowline, and inferior to the above-the-snowline variety in living above the snowline. Then natural selection would keep the two types separate, with only a thin band of hybrids between them. The amount of gene flow between the two varieties would be small, and natural selection would keep the two varieties distinct.
Just because there is no geographical barrier between them doesn't mean that they must blend.
Does that start to answer your question?

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Blue Jay
Member (Idle past 2698 days)
Posts: 2843
From: You couldn't pronounce it with your mouthparts
Joined: 02-04-2008


Message 4 of 16 (511693)
06-11-2009 8:59 AM
Reply to: Message 1 by InGodITrust
06-11-2009 4:07 AM


Hi, InGodITrust.
Welcome to EvC!
IGIT writes:
So if there are no geographical barriers to separate different groups of a species, can mere distance serve to isolate them?
There is an ecological phenomenon referred to as the Allee effect, which is that reproduction decreases as a species's density decreases.
So, if you have a population that is spread out over a very wide area, and has different densities in different parts of its range, you will find little interbreeding in low-density areas and more breeding in high density areas.
Thus, you can have new mutations build up quickly in the densely populated areas, and diffuse very slowly through the sparsely populated areas. So, two densely populated areas separated by a wide stretch of sparsely populated area can accumulate mutations that don't cross between populations very readily.
-----
Similar to what Dr Adequate is saying, many species of fly and non-stinging wasp lay their eggs inside a host plant, and the larvae develop inside the host (these insects are called "parasitoids"). Some of these parasitoids may use multiple different host species. But, each plant will exert different selection pressures on the insect, so it's possible that those laying eggs in different plants will start to diverge.
I supplied a link to a discussion about the topic of parasitoid flies a few months ago: Speciation in Fruit Flies.
-----
You can also have speciation by sexual selection.
If females of a species prefer either of two mutually-exclusive male phenotypes (external traits), you can easily restrict gene flow between male types, provided the female preference is genetic (and there are many cases when it is).
-----
There are probably many other examples people could give, too, but these are sufficient for now.

-Bluejay (a.k.a. Mantis, Thylacosmilus)
Darwin loves you.

This message is a reply to:
 Message 1 by InGodITrust, posted 06-11-2009 4:07 AM InGodITrust has replied

Replies to this message:
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InGodITrust
Member (Idle past 1669 days)
Posts: 53
From: Reno, Nevada, USA
Joined: 05-02-2009


Message 5 of 16 (511738)
06-11-2009 1:34 PM
Reply to: Message 4 by Blue Jay
06-11-2009 8:59 AM


Thanks for the replies and examples. You've answered my question. Basically, natural selection can act faster than crossbreeding over a wide range can counter it.
This is important to me when contemplating the theory of evolution, because it effects the speed at which evolution can proceed. It would take a lot longer if evolution had to wait for a species to migrate through a narrow pass in a barrier and fill the other side, or for geologic upheaval.
Edited by InGodITrust, : No reason given.
Edited by InGodITrust, : No reason given.
Edited by InGodITrust, : No reason given.
Edited by InGodITrust, : No reason given.

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


Message 6 of 16 (511772)
06-11-2009 7:45 PM
Reply to: Message 5 by InGodITrust
06-11-2009 1:34 PM


and breeding times
Hi InGodITrust, and welcome to the fray.
Basically, natural selection can act faster than crossbreeding over a wide range can counter it.
Remember that the key to natural selection is that the organisms survive to breed: no survival, and no contribution to the next generation; no breeding, and no contribution to the next generation. You need both.
Another example of how speciation can occur is with timing of breeding: if one population breeds at one time of the year and another population breeds at another time of year, then they can diverge even though they live quite close.
In the early study of malaria, scientists were puzzled as some populations of a mosquito species seemed to be carriers, while other did not. Turns out one breeds in the morning and the other in the afternoon, and further investigation determined they were different species, no longer able to interbreed.
Enjoy.

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This message is a reply to:
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CosmicChimp
Member
Posts: 311
From: Muenchen Bayern Deutschland
Joined: 06-15-2007


Message 7 of 16 (513514)
06-29-2009 12:04 PM
Reply to: Message 5 by InGodITrust
06-11-2009 1:34 PM


How Do You Counter Natural Selection?
Can it be that you're attributing too much of an active roll to natural selection? It's not a thinking entity. Crossbreeding doesn't "counter it." Natural selection is more like the consequences of the circumstances facing organisms.
Edited by CosmicChimp, : fixed the subtitle

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Replies to this message:
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Taz
Member (Idle past 3291 days)
Posts: 5069
From: Zerus
Joined: 07-18-2006


Message 8 of 16 (513556)
06-29-2009 11:04 PM
Reply to: Message 1 by InGodITrust
06-11-2009 4:07 AM


IGIT writes:
Isn't isolation neccesary for evolution?
Nope. Others have explained so I'm not going to waste my time.
So if there are no geographical barriers to separate different groups of a species, can mere distance serve to isolate them?
Yes. Others have explained so I'm not going to waste my time.
Hypothetically, I'm thinking of a species of hare that has a range...let's say 300 miles wide. Wouldn't the genes of all the would-be varieties keep criss-crossing across the range, and keep the species pure? Or if the distance is great enough, can varieties form?
I'd like to point out that you're also forgetting about time as a barrier.
Yes, the genes of all the would-be varieties would keep criss-crossing. But that doesn't necessarily mean a species remain "pure", whatever that means. We know that mutation is bound to occur. And every once in a while, a mutation is bound to create a new phenotype, adding variation to the gene pool. The population as a whole just evolved.
The population of hare at the said location isn't the same population of hare at the same location a million years ago. And it won't be the same population of hare a million years from now. Enough phenotypic changes over long periods of time could act as a barrier and give us a completely new species.

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 Message 1 by InGodITrust, posted 06-11-2009 4:07 AM InGodITrust has not replied

  
Taz
Member (Idle past 3291 days)
Posts: 5069
From: Zerus
Joined: 07-18-2006


Message 9 of 16 (513557)
06-29-2009 11:06 PM
Reply to: Message 5 by InGodITrust
06-11-2009 1:34 PM


IGIT writes:
Thanks for the replies and examples. You've answered my question. Basically, natural selection can act faster than crossbreeding over a wide range can counter it.
This is important to me when contemplating the theory of evolution, because it effects the speed at which evolution can proceed. It would take a lot longer if evolution had to wait for a species to migrate through a narrow pass in a barrier and fill the other side, or for geologic upheaval.
Um, I don't think you understand what the theory of evolution is. At this point, I'm not sure how to explain it to you to clear the misconceptions you've shown in the quoted post above. I'll get back to you on this.

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pandion
Member (Idle past 3000 days)
Posts: 166
From: Houston
Joined: 04-06-2009


Message 10 of 16 (513561)
06-29-2009 11:37 PM
Reply to: Message 7 by CosmicChimp
06-29-2009 12:04 PM


Re: How Do You Counter Natural Selection?
CosmicChimp writes:
Can it be that you're attributing too much of an active roll to natural selection? It's not a thinking entity.
I think that you have misunderstood what was intended. I don't think that he was attributing any intent. I believe that he is saying that natural selection on the extremes of a widely distributed species will cause those sub-populations to diverge faster than "crossbreeding", i.e., gene flow between the sub-populations, can counter it. Thus, speciation can occur in a contiguous population.
Crossbreeding doesn't "counter it."
Of course not. Natural selection will always act to adapt the species to the environment. However, gene flow does prevent speciation.
Natural selection is more like the consequences of the circumstances facing organisms.
Differential reproductive success. That success is the result of heritable characters that are adaptive to the environment.

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Replies to this message:
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CosmicChimp
Member
Posts: 311
From: Muenchen Bayern Deutschland
Joined: 06-15-2007


Message 11 of 16 (513562)
06-30-2009 12:03 AM
Reply to: Message 10 by pandion
06-29-2009 11:37 PM


Mixing prevents clumping
Nice post I agree with most of it. I am mainly trying to counter the personification of Natural selection. All of these verbs keep getting attached to it that I just can't make myself accept no matter how hard I try over all these years. =)
Even you say this tidbit in your above clarification of the other man's post:
Natural selection will always act to adapt the species to the environment.
I see Natural Selection as a passive force. There's nothing behind it. To me the "moving components" are the organisms, their genes and the genetic drift in the population.
{ABE}Plus, I'm trying to find out whether or not InGodITrust believes that NS is a god or maybe even a devil, thinking entities he would presumably believe are capable of action.
Edited by CosmicChimp, : zpe11in
Edited by CosmicChimp, : added new material

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Replies to this message:
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Coyote
Member (Idle past 2106 days)
Posts: 6117
Joined: 01-12-2008


Message 12 of 16 (513563)
06-30-2009 12:19 AM
Reply to: Message 11 by CosmicChimp
06-30-2009 12:03 AM


Re: Mixing prevents clumping
I see Natural Selection as a passive force. There's nothing behind it. To me the "moving components" are the organisms, their genes and the genetic drift in the population.
Sorry, I can't agree with that.
"Natural selection" is a term scientists use to describe a very real phenomenon whereby some critters reproduce more successfully than others. The environment acts as the selector, and the range of variability within a population is the subject of that selection.
One end of the bell curve will have a much tougher time--for any given trait--than the other. Add up all of those hundreds or thousands of bell curves within a population, factor in the correct differential weights for each, and you can begin to model the selection pressures. We can't do that all that well yet, but that doesn't mean that the phenomenon doesn't exist.

Religious belief does not constitute scientific evidence, nor does it convey scientific knowledge.

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pandion
Member (Idle past 3000 days)
Posts: 166
From: Houston
Joined: 04-06-2009


Message 13 of 16 (513564)
06-30-2009 12:26 AM
Reply to: Message 4 by Blue Jay
06-11-2009 8:59 AM


Bluejay writes:
...many species of fly and non-stinging wasp lay their eggs inside a host plant, and the larvae develop inside the host (these insects are called "parasitoids"). Some of these parasitoids may use multiple different host species. But, each plant will exert different selection pressures on the insect, so it's possible that those laying eggs in different plants will start to diverge.
What's worse than finding a worm in an apple? So everyone knows that apples sometimes have worms, actually the larvae of the apple maggot fly. The case is interesting because apples are not native to North America. They were cultivated from seeds brought from Europe. Thus, apple parasitoids didn't exist in North America. John Chapman (Johnny Appleseed) brought apple seeds from his native Massachusetts (where they had been cultivated from seeds brought from Europe) and planted apples in the Ohio River valley. He did that in the 1st half of the 19th century. He died in 1845. Shortly after that, in the 1850s, worms began to appear in apples. There are a couple of possibilities - special creation by a magical spirit, or the infestation of apples by a native species. The latter seems to be the case since the apple maggot fly is identical to the hawthorn maggot fly. There are several species of hawthorn in at least two genera that I know of in the family Rosaceae and the sub-family Maloideae that are all infested with the hawthorn maggot fly. The hawthorns, as well as the fly, are native to North America. As it happens, the apple is also in the Rosaceae family and the Maloideae sub-family. The problem for maggot flies is that they do not set fruit at the same time. They are separated by a period of weeks. But somehow, some poor female maggot fly was early/late (I'm not sure which) by enough time that the usual host species (the hawthorn) was not available, so it settled on an apple tree.
Studies have indicated that hawthorn maggot flies and apple maggot flies rarely, if ever, interbreed. Their reproduction is in sync with the time the various plants set fruit. Thus, they reach sexual maturity some weeks apart. Moreover, they just seem to prefer the host on which they were born.
There is also the pear maggot fly. Pears, like apples, are not native to North America, but they are in the same family and sub-family. Thus, they have also been infested by maggot flies. These various flies, even though they may inhabit the same territory, rarely interbreed. They prefer their particular host when there is a choice (established by experimentation) and their time of sexual maturity is in cycle with that host.
If these various parasitoids are not separate species, they are at the least obvious examples of incipient species. They are evidence of the fact that evolution happens, and in fact, that macroevolution happens or is in the process of happening.
The term for this, by the way, is sympatric specieation, i.e., the divergence of a single species into two (or more) species as events contingent on environmental opportunities.
But they are still maggot flies and but a single pair was aboard the ark with Noah.
Edited by pandion, : No reason given.

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pandion
Member (Idle past 3000 days)
Posts: 166
From: Houston
Joined: 04-06-2009


Message 14 of 16 (513567)
06-30-2009 12:52 AM
Reply to: Message 11 by CosmicChimp
06-30-2009 12:03 AM


Re: Mixing prevents clumping
CosmicChimp writes:
Nice post I agree with most of it.
Thanks.
I am mainly trying to counter the personification of Natural selection. All of these verbs keep getting attached to it that I just can't make myself accept no matter how hard I try over all these years. =)
Far be it from me to personify natural selection. We know that there is no intent or purpose to natural selection. Natural selection is the differential reproductive success of individuals that possess heritable characters that lend a survival advantage in a particular environment.
Even you say this tidbit in your above clarification of the other man's post:
quote:
Natural selection will always act to adapt the species to the environment.
Indeed. But it is a limit of the language and your understanding of my intent. Natural selection does "act," but that does not imply intent. We can't make up new words for each and every natural phenomenon. In science we use words that may also be used in common discourse. We assume that, in the discussion of science, the other party understands the "special case" meaning of terms. Certainly, this has not been the case in discussions with creationists who continue to insist that evolution is only a theory, while ignoring the fact that gravity, light, heliocentric solar system, etc. are too.
{ABE}Plus, I'm trying to find out whether or not InGodITrust believes that NS is a god or maybe even a devil, thinking entities he would presumably believe are capable of action.
I don't think so. I'm pretty sure that if InGodITrust is a theist, he does not consider NS to be either a god or a devil. Hopefully, he does not believe that natural processes are capable of intent.

This message is a reply to:
 Message 11 by CosmicChimp, posted 06-30-2009 12:03 AM CosmicChimp has replied

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CosmicChimp
Member
Posts: 311
From: Muenchen Bayern Deutschland
Joined: 06-15-2007


Message 15 of 16 (513568)
06-30-2009 1:07 AM
Reply to: Message 12 by Coyote
06-30-2009 12:19 AM


Re: Mixing prevents clumping
Am I not correct when I contend that the term Natural selection is a sort of cobbled together (and inaccurate) way of expressing the ideas you quite well gave in your above post Coyote? I still cling to the notion that it is not an active force, it is a passive force. It does no selecting in and of itself. It doing so would even imply that it is deciding. These verbs are limited to living beings (or some mechanisms of chance I suppose). You cannot apply them to an inanimate phenomena like NS. Your post is quite good but please realize that I am objecting to the personification of NS.
Also when I said "... nothing behind it." I did not mean as I think you may have interpreted that it is immaterial or of no consequence. I have always been a strong adherent to the ToE since I first learned about it. Accordingly I wouldn't want you to think I thought NS was anything other than a profound and mighty force or phenomena in the natural universe.

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