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Author Topic:   Stasis and Evolution
Blue Jay
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From: You couldn't pronounce it with your mouthparts
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Message 1 of 2 (528249)
10-05-2009 11:17 AM


Near the end of Calypsis4's "Living fossils" thread, Arphy expressed an interest in debating the importance of stasis in evolutionary biology (Source: Arphy's Summation).
It is his contention that the ToE should not allow the long bouts of stasis that we see in the fossil record. Elsewhere, other creationists (including Kaichos Man) have brought up issues related to the rate of change and the quantity of change.
I think the topic deserves some special attention, so I propose a thread to discuss stasis in evolution.
My perspective is that Arphy’s contention is a misunderstanding of evolution that stems mainly from the format of discourse in the biological sciences. Biologists talk about mutation and natural selection, and often characterize them as mechanisms, which creationists find troubling because of the apparent circularity or vague, story-like feel to the definition.
In a post in the free-for-all Lossy Adaptation via..., I gave a description of the actual mechanisms behind mutation and natural selection (AChristianDarkly used a three-part, A-B-C model to link a source, a mechanism and an outcome, and that’s the motif I used in that post).
The problem is that neither mutation nor natural selection really refers to anything mechanistic. Biology has hundreds, probably thousands of actual mechanisms at play, and these can be collected into two groups based on the effects they have on organisms:
  • Mutation: random processes that add diversity (these mechanisms are usually chemical processes that act at the molecular level)
  • Natural Selection: non-random processes that diminish diversity (these mechanisms are ecological processes that act at the organismal level).
With this in mind, one should remember that, when a biologist says, Natural selection favors the fit, he is not referring to an actual force or entity that is causing some things to die, while allowing others to live. Rather, he is referring to a collection of mechanisms (or a subset of mechanisms from that collection) that are unrelated, but relatively similar in outcome.
Examples of mechanisms include predation, pathogens, resource fluctuations, sparring for dominance, mate preferences, etc. They are all different, and each has varying shades of influence on fitness depending on the effectiveness of the predator, the severity and character of the resource flux, the lethality of the pathogen, the rules of the sparring contest, or the personality of the choosy mate.
Since all of these mechanisms are part of evolution, and since they don’t all have the same influence in all scenarios, we should expect to see a variety of responses (in terms of quantity, direction, rate and form of the response) in different animals. And, organisms will have to deal with multiple mechanisms over time, so sequence will also come into play. So, there are literally millions of ways these different mechanisms can interact to shape evolution of life on Earth, and that’s why there are literally millions of different types of organisms, each responding to a different set of pressures that act on different time scales, with different intensities, and different fluctuations.
Here is a tabular representation, with a number of pressures, or mechanisms, listed across the top, and the characteristics of the response along the side:
Response of one organism to a plethora of natural selection mechanisms
Predator 1Predator 2Pathogen 1Pathogen 2Prey 1Prey 2Water availabilityStrength of male competitorsPreference of females
Amount of change0.143.156.63.012.782.00.440.0990.1
Direction of change1.04.12.30.80.199.134.4215.362.1
Rate of change6.0813.145.234.4512.316.187.726.517.13
Form of changeABCDEFGHI
(Don’t get hung up on the numbers: they’re just fillers). This is just for one organism. It is conceivable, (and probable, under the evolutionary model), with so many different possible ways to respond to so many different mechanisms, which act on so many different temporal and spatial scales, that there would be great variety in the outcome of selection on different lineages of organisms.
So, in summary, my position is that Arphy’s view (that stasis should not happen if things evolve) comes from an oversimplified understanding of evolution, and of the processes and functions of life.
Forum recommendation: Biological Evolution"
Edited by Bluejay, : column missing from table
Edited by Bluejay, : Better formatting and a couple additions around the table

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

AdminNosy
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Message 2 of 2 (528253)
10-05-2009 11:28 AM


Thread Copied to Biological Evolution Forum
Thread copied to the Stasis and Evolution thread in the Biological Evolution forum, this copy of the thread has been closed.

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