Ask some questions about evolution here.
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08-10-2015, 05:02 PM
Ask some questions about evolution here.
(08-10-2015 04:51 PM)Chas Wrote:  
(07-10-2015 06:31 AM)TheBeardedDude Wrote:  No, punctuated equilibrium is different. It isn't only a matter of timescale.

No, that's just like the micro - macro evolution baloney.

Quote:Punctuated equilibrium postulates that some species (not all because some examples of evolution clearly are a better fit for gradualism) remain constant (in stasis) with respect to their morphological disparity over time (with the only variability being fluctuations about a mean with no net change) because there is no selection pressure to drive change during stasis.

Which is what I said.

Quote:For instance, we see it quite often in the fossil record (especially with invertebrates like brachiopods and trilobites and bivalves, etc) where some environments are constant for millions of years and as a result, the same species will persist with little to no morphological change over the same stretch of time.

Which is what I said.

Quote:Basically, if there is no selection pressure to drive morphological change, there won't be any morphological change.

Which is what I said.

Quote:That is the equilibrium part of it (stasis). But periods of stasis are punctuated by intervals of rapid change. This rapid change is some alteration to the selection pressures that had remained constant, that then drives either adaptation (and therefore morphological change) or extinction.

Which is what I said.

Quote:So, gradualism is essentially constant change over time (no meaningful deviation from the rate of evolutionary change) but punctuated equilibrium are periods of stasis (no net change) punctuated by rapid (short intervals of time) evolutionary change. For the first image, the horizontal lines represent no net change in the punc eq model, in reality it would be more like b in the second image where there is variability but no net change. In the second image, c (or a) would be similar to punc eq. where a change in selection pressure causes a shift in the mean, speciation, and e would be what some might call punctuated gradualism.

I did not contrast "punctuated equilibrium" with "gradualism". I am saying all of evolution is punctuated equilibrium; they are one and the same. There aren't two kinds of evolution.

Quote:[Image: outil_bleu09_img02.jpg]
(the y-axis is labeled funny in this one. I don't know what "evolution" is really supposed to mean here, but we can assume it means either change in allele frequency, for the biologists, or morphological change)

If you stand back, both pictures look the same.

Quote:[Image: F1.large.jpg]

Sorry, what's the point of that pic? Consider

The point of the second image is to show that variance can mimic directional trends if viewed at timescales that are too short. And that what appears to be gradual change, is variance within stasis.

Stasis would be defined in evolution as no statistically significant change from the beginning value. Punctuated equilibrium is stasis followed by a period of sudden (geologically) change followed by stasis or gradualism. Gradualism is change such that the mean at any given time within the geologic record is statistically different from the starting value and that the change is directional.

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08-10-2015, 05:07 PM (This post was last modified: 08-10-2015 05:14 PM by TheBeardedDude.)
Ask some questions about evolution here.
Had to delete it, couldn't get the pictures I wanted to link.

Here, check this out. http://evolution.berkeley.edu/evolibrary...ctuated_01

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08-10-2015, 05:20 PM
Ask some questions about evolution here.
And both gradualism and punctuated equilibrium are susceptible to the same selection pressures. It's the rate of change that differs.

And gradualism has no period of stasis. It is a constant rate.

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