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Punctuated Equilibrium Discussion

RuvDraba
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5/25/2016 7:55:38 PM
Posted: 6 months ago
Punctuated Equilibrium is an idea about evolution proposed in the 1970s by paleobiologists Niles Eldridge and Stephen Jay Gould. [https://en.wikipedia.org...] It wasn't the last refinement to understanding species traits -- that's still continuing -- but was one of the last big changes to species modelling before evolution became generally accepted by biologists and paleologists as the only viable model explaining speciation, and providing a comprehensive understanding of how it all fit together.

The idea behind PE is that rather than new species being formed from gradual progressive improvements occurring over the life of a species, big improvements in adaptation occur through environmental mechanisms that suddenly create new species.

As far as I can recall, we haven't talked all that much about Punctuated Equilibrium here in Science. So it might come as a surprise to see it talked about in the Religion forum (and it may come as even more of a surprise when you see the Original Poster initiating the discussion. )

Anyway, against all odds, there's a serious discussion about PE under Religion, and I thought I'd link it here for the interest of members who (understandably) might not frequent that forum (or only page through it, screaming, with their eyes half-shut.) The discussion started from a thoughtful question by member Danb6117, and I acknowledge his contribution. Here's a link from his question onward: [http://www.debate.org...]
Chaosism
Posts: 2,674
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5/25/2016 8:18:36 PM
Posted: 6 months ago
At 5/25/2016 7:55:38 PM, RuvDraba wrote:
Punctuated Equilibrium is an idea about evolution proposed in the 1970s by paleobiologists Niles Eldridge and Stephen Jay Gould. [https://en.wikipedia.org...] It wasn't the last refinement to understanding species traits -- that's still continuing -- but was one of the last big changes to species modelling before evolution became generally accepted by biologists and paleologists as the only viable model explaining speciation, and providing a comprehensive understanding of how it all fit together.

The idea behind PE is that rather than new species being formed from gradual progressive improvements occurring over the life of a species, big improvements in adaptation occur through environmental mechanisms that suddenly create new species.

As far as I can recall, we haven't talked all that much about Punctuated Equilibrium here in Science. So it might come as a surprise to see it talked about in the Religion forum (and it may come as even more of a surprise when you see the Original Poster initiating the discussion. )

Anyway, against all odds, there's a serious discussion about PE under Religion, and I thought I'd link it here for the interest of members who (understandably) might not frequent that forum (or only page through it, screaming, with their eyes half-shut.) The discussion started from a thoughtful question by member Danb6117, and I acknowledge his contribution. Here's a link from his question onward: [http://www.debate.org...]

I saw that this hadn't come up in the referenced thread as of yet, but I think that Punctuated Equilibrium is often misconceived as a non-gradual saltation theory (https://en.wikipedia.org...[biology]), and in looking at the "flat" phyletic diagrams (https://en.wikipedia.org...), I can see where one could derive this. Of course, a driving bias to negatively interpret evolutionary notions in the most ridiculous way possible helps, too. From the Wiki Source:

Confusion with punctuated equilibrium
It is a popular misconception that punctuated equilibrium is a saltationist theory, often mistaken for Richard Goldschmidt's hypothesis of "Hopeful Monsters." However, punctuated equilibrium refers instead to a pattern of evolution where most speciation occurs relatively rapidly from a geological perspective (tens of thousands of years instead of millions of years), but through neo-Darwinian evolution, not by saltations. Punctuated equilibrium differs from hopeful monsters in that the former acts on populations rather than individuals, is theoretically more gradual (which proposes to take 50,000 to 100,000 years), functions by the evolution of reproductive isolation (through mechanisms such as allopatric speciation), and the latter says nothing of stasis.

Supplemental Source: http://www.stephenjaygould.org...
RuvDraba
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5/25/2016 8:28:10 PM
Posted: 6 months ago
At 5/25/2016 8:18:36 PM, Chaosism wrote:
I saw that this hadn't come up in the referenced thread as of yet, but I think that Punctuated Equilibrium is often misconceived as a non-gradual saltation theory

Yes. Mayr picks up on this too, and points out that geographic speciation was never other than a gradualist mechanism [http://www.genetics.org...][http://www.stephenjaygould.org...]

I didn't mention it to Dan yet, because he's already chewing on a lot, but he's a methodical reader and an astute thinker. I'm sure it'll come up. :)
keithprosser
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5/25/2016 9:41:43 PM
Posted: 6 months ago
It's interesting why the idea of 'uniformish gradualism' came about in the first place.

Recall Darwin's original theory was purely 'natural selection' - he had nothing to say about mutation or genes because they weren't known about in his day. HOwever Darwin knew that there was always some natural variation between the individuals that made up a population - some individuals were bigger than others, some were less hairy and so on, 'for reasons unknown' at the time.

As such variation between individuals was - presumably - always present and natural selection always operates, ergo evolution is a continuous, gradual and fairly uniform process. Had people known about genes and mutation they might have come to a different conclusion, but that knowledge was not availble in 1859.

It seems that until E&G came along 'uniform gradualism' was an assumption people didn't fully realise they were making. 'Linear' models are easier to work with, and if they seem to work people will stick with them for obvious reasons. Until there were advances in the ability to date fossils accurately (and having enough fossils to date) there would be reason to question (or notice) the assumption of linearity.

At the time PE was often touted as a challenge to the theory of evolution, but in reality that was 'hype', some of it encouraged by Gould himself. In reality, PE was a minor amendment to evolutionary theory. The assumed linearity of evolution was never a central plank of the theory anyway. PE didn't upset even small fruit bowl, let alone an apple cart.
RuvDraba
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5/25/2016 11:21:41 PM
Posted: 6 months ago
At 5/25/2016 9:41:43 PM, keithprosser wrote:
It's interesting why the idea of 'uniformish gradualism' came about in the first place.
I think that's a fair take, Keith.

I'd suggest though that Darwin wasn't himself wedded to the idea of uniform selection rates, and in fact knew the opposite. Uniform rates of generational variation, perhaps, he might endorse, but he knew that at some point, finches had flown to adjacent islands, and some had survived better than others. Since the principal benefit of adaptation is improved survival rates, he must've known -- or suspected -- that there were plenty of deaths in new or changing environments (especially since this is exactly what happened when colonists tried Old World agriculture in New World lands he visited in just this period.) Here for example, he's talking about mass deaths and extinctions that might arise from climate change:

We shall best understand the probable course of natural selection by taking the case of a country undergoing some slight physical change, for instance, of climate. The proportional numbers of its inhabitants will almost immediately undergo a change, and some species will probably become extinct. We may conclude, from what we have seen of the intimate and complex manner in which the inhabitants of each country are bound together, that any change in the numerical proportions of the inhabitants, independently of the change of climate itself, would seriously affect the others. [http://www.gutenberg.org...]

So he knew survival rates must fluctuate in response to new or changed environments. Even with uniform generational variations, that's not consistent with uniform rates of species change.

But Darwin had great trouble getting his ideas accepted, and is known to have compromised them around the edges in order to make them easier to understand and accept.

For example, the notion of 'survival of the fittest' wasn't one he readily subscribed to. It was language adopted in later editions of On the Origin of Species, and borrowed from philosopher Herbert Spencer. Spencer had a sort of progressive, moralistic view of evolution, and I haven't found that view expressed in The Origin of Species, except in the adoption of Spencer's Language in the title of a single chapter. It seems that Darwin found the struggle to survive captured by the term Survival of the Fittest preferable to the idea of ordained predestination that many were construing from Natural Selection. Even so, he knew that some variations would not be beneficial:

The variability, which we almost universally meet with in our domestic productions is not directly produced [...] by man; he can neither originate varieties nor prevent their occurrence; he can only preserve and accumulate such as do occur. [...] Can it then be thought improbable, seeing that variations useful to man have undoubtedly occurred, that other variations useful in some way to each being in the great and complex battle of life, should occur in the course of many successive generations? If such do occur, can we doubt (remembering that many more individuals are born than can possibly survive) that individuals having any advantage, however slight, over others, would have the best chance of surviving and procreating their kind? On the other hand, we may feel sure that any variation in the least degree injurious would be rigidly destroyed. This preservation of favourable individual differences and variations, and the destruction of those which are injurious, I have called Natural Selection, or the Survival of the Fittest. Variations neither useful nor injurious would not be affected by natural selection, and would be left either a fluctuating element, as perhaps we see in certain polymorphic species, or would ultimately become fixed, owing to the nature of the organism and the nature of the conditions. [http://www.gutenberg.org...]

It wouldn't damage the science if Darwin had shared those views, since it's okay for scientific conjectures to be wrong; I just don't think he actually did.
keithprosser
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5/25/2016 11:46:45 PM
Posted: 6 months ago
Quite. PE is, let's not forget, a gradualist theory. All PE does is make explicit that evolution is 'variable speed gradual', not 'constant speed gradual'. Even the 'spurts' of evolution suggested by PE are very slow by human standards, just not quite as slow as at other times!

I am sure that Darwin never insisted evolution was a simple 'linear function of time'. I'm not sure anybody working in the field did think it was simply linear - but it was better 'copy' if E&G were presented as radical mavericks challenging the foundations of science than the truth which was that they had dotted an i and/or crossed a t.
Axonly
Posts: 1,802
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6/6/2016 7:57:24 AM
Posted: 6 months ago
At 5/25/2016 7:55:38 PM, RuvDraba wrote:
Punctuated Equilibrium is an idea about evolution proposed in the 1970s by paleobiologists Niles Eldridge and Stephen Jay Gould. [https://en.wikipedia.org...] It wasn't the last refinement to understanding species traits -- that's still continuing -- but was one of the last big changes to species modelling before evolution became generally accepted by biologists and paleologists as the only viable model explaining speciation, and providing a comprehensive understanding of how it all fit together.

The idea behind PE is that rather than new species being formed from gradual progressive improvements occurring over the life of a species, big improvements in adaptation occur through environmental mechanisms that suddenly create new species.

As far as I can recall, we haven't talked all that much about Punctuated Equilibrium here in Science. So it might come as a surprise to see it talked about in the Religion forum (and it may come as even more of a surprise when you see the Original Poster initiating the discussion. )

Anyway, against all odds, there's a serious discussion about PE under Religion, and I thought I'd link it here for the interest of members who (understandably) might not frequent that forum (or only page through it, screaming, with their eyes half-shut.) The discussion started from a thoughtful question by member Danb6117, and I acknowledge his contribution. Here's a link from his question onward: [http://www.debate.org...]

Punctuated Equilibrium makes me <3
Meh!