Punctuated Equilibrium and Stasis
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17-06-2011, 09:03 AM
Punctuated Equilibrium and Stasis
For the most part any discussions on evolution on this and every other forum I read are centered around gradualism (the primary concept devised by Darwin). In a gradualism scenario all populations are in perpetual transistion from previous generations to future generations. That is evolution is a step by step process that occurs every generation very slowly that eventually results in what we would classify as a new species. This most certainly occurs in species that exist today and in the past but it is not the only possibility. There exists Eldredge and Gould's concept of Punctuated Equilibrium and Stasis.

In this scenario a species will exist for a geologically significant amount of time in stasis (that is unchanged). There may be some vartiation through time but the overall change is negligible (some variation about a mean for example). Good examples include trilobites, bivalves, gastropods and numerous other invertebrates (I am more familiar with the invertebrates so I will stick with them). These periods of stasis are interrupted by some punctuation event. This event could be an increase in the rate of climate change (such as the formation of ice on Antarctica or the rapid release of large amounts of mehtane gas from the destabalization of methane clathrates). These events induce a rapid speciation event (rapid would still mean several generations). The reasons are fairly simple. 1) If you are well suited to your environment then there is no need for any major changes. This would mean that species would prefer stasis since it would be the most cost efficient method in terms of energy use. 2) Any sufficiently large population would have such a large gene pool that shifting the population in any one direction under normal conditions would be nearly impossible. In order to change a large population it needs to be reduced (an extinction event like a large bolide for example) or seperated spatially (like being geographically seperated by an ocean/mountain chain/river/etc...). Once the size of the poulation is reduced and the size of the gene pool is shrunk change can occur more rapidly (I am a geologist so rapid for me is still a pretty dadgum long time).

I just want to see what you guys think or know about stasis and Punctuated Equilibrium.
*Note: I am in the middle of nowhere Wyoming for another few weeks so I may not be capable of responding but I will try.

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17-06-2011, 09:25 AM
RE: Punctuated Equilibrium and Stasis
Well, The Hardy-Weinberg Equilibrium mentions that if a population is large enough such that any loss of an organism will not affect the gene frequency of the population, there is random mating, there is no natural selection, no mutation, and no gene flow, evolution and thus speciation should not occur.

No mutation is impossible, but the others are possible. As long as the environment is isolated, there is enough resources, as you mentioned, there is no need to adapt. Such conditions are rare, but possible.

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17-06-2011, 01:00 PM
RE: Punctuated Equilibrium and Stasis
I'd say it definitely has validity also to an extent Hardy-Weinberg does. Though according to Darwin sexual selection is part of the natural form and still occurs within such groups. The idea of random mating is only viable if the individual is not the chooser. A study with guppies found that if there are no predators present in their environment the females will prefer the guppies which stand out the most and there will be a much larger number of male guppies which contrast the environment

The main reason that we always discuss gradual evolution is because that is the huge debate that we're trying to get across. Usually our discussions on the topic are dealing with the cultural argument rather than seeking a better understanding of all the science.

Punctuated equilibrium and stasis is a good answer for distinct variations, but for me it allows for less diversity in species as changes are then confined to specific events. I would have to suggest not choosing one over the other but accepting that there are multiple ways in which evolution can occur.

I'm not a non believer, I believe in the possibility of anything. I just don't let the actuality of something be determined by a 3rd party.
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17-06-2011, 02:00 PM
RE: Punctuated Equilibrium and Stasis
There is no doubt that both occur simultaneously but rather stasis and punc eq seem to be ignored. Variation still occurs within populations that are in a period of stasis. These variations that we see on short timescales are essentially insignificant over longer intervals. A good example would be us. There is a lot of variation amongst humans as far as size, color and fitness are concerned but overall the population has remained unchanged for several thousand generations (excluding technology, medicine and agriculture). Punc eq and stasis are concerned with the overall variation on longer time intervals than just generation to generation and is variation on these timescales that leads to speciation.

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17-06-2011, 02:11 PM
RE: Punctuated Equilibrium and Stasis
I think when we discuss things further we discuss all of evolution more often, but this site is often hounded by prove Darwin demands. I agree that it's excessively important in the understanding of evolution and find this to be a great study, I'll be reading some books on it once I purchase them so that I have a more comprehensive grasp of the ideas. Thanks for mentioning this as I'm gaining a better grasp of it and becoming more interested. I took a long break from intellectual pursuits due to the inability to discuss my findings with others well. Now with TTA I'm regaining my zeal for knowledge.

I'm not a non believer, I believe in the possibility of anything. I just don't let the actuality of something be determined by a 3rd party.
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18-06-2011, 11:11 AM
RE: Punctuated Equilibrium and Stasis
Would this be why there are living fossils?

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08-07-2011, 12:51 PM
RE: Punctuated Equilibrium and Stasis
'Living fossils' is a misleading term. This implies that an organism has not changed at all since it was first discovered in the fossil record. What we actually see is that there is change but for some species the change is minimal. Most species (I have to use the term most rather loosely here) do not change very much over a few million years unless some punctuation event causes a disruption within their environment to necessitate change. For some organisms (living fossils) there has been little to no change in the environment they live in since they first appeared in the fossil record and therefore the mechanism for change is not as strong.

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11-08-2011, 09:51 AM
RE: Punctuated Equilibrium and Stasis
(17-06-2011 09:03 AM)TheBeardedDude Wrote:  2) Any sufficiently large population would have such a large gene pool that shifting the population in any one direction under normal conditions would be nearly impossible. In order to change a large population it needs to be reduced (an extinction event like a large bolide for example) or seperated spatially (like being geographically seperated by an ocean/mountain chain/river/etc...). Once the size of the poulation is reduced and the size of the gene pool is shrunk change can occur more rapidly (I am a geologist so rapid for me is still a pretty dadgum long time).

Not a scientist, just an interested layperson, so I apologize if this is obvious, but the above statement raised a speculation on my part, interested to hear what those of you who know this stuff think:

Is there a point at which a large population can in fact create its own isolation? Obviously this would be tied to the specific species in question and their locomotive capabilities, but can there be a population where the individuals at one geographic edge are sufficiently isolated from the opposite edge that in fact, without any natural geographic barriers other than sheer physical distance, they begin to evolve separately? To put it another way, is there an upward limit on population relative to locomotion where evolution becomes inevitable?
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11-08-2011, 11:24 AM
RE: Punctuated Equilibrium and Stasis
That is an intriguing concept but I do not know of any specific examples of such. I assume what your asking is there a population that is so large that it segregates itself by some method thus driving evolutionary change? If so humans would be a good example. Before international travel remixed our populations we had a lot of variation that was the result of tribal segregation. These different groups and tribes left Africa and colonized other areas. Geography and climate were important drivers for evolution in this case so it is not strictly what you were asking for.

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11-08-2011, 11:34 AM
RE: Punctuated Equilibrium and Stasis
(11-08-2011 11:24 AM)TheBeardedDude Wrote:  That is an intriguing concept but I do not know of any specific examples of such. I assume what your asking is there a population that is so large that it segregates itself by some method thus driving evolutionary change? If so humans would be a good example. Before international travel remixed our populations we had a lot of variation that was the result of tribal segregation. These different groups and tribes left Africa and colonized other areas. Geography and climate were important drivers for evolution in this case so it is not strictly what you were asking for.

Yes, that's the gist of it if I'm reading you correctly. Humans are too messy a species (what with our artificial travel capabilities) to demonstrate this effectively though. I was thinking slow moving or small ground animal without the need for large territorial hunting grounds or the like. Perhaps some insect species or even a micro-organism?
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