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Author Topic:   Reduction of Traits by Natural Selection (Faith and Bluejay Only)
Blue Jay
Member (Idle past 2697 days)
Posts: 2843
From: You couldn't pronounce it with your mouthparts
Joined: 02-04-2008


Message 1 of 2 (553157)
04-01-2010 4:59 PM


GREAT DEBATE: FAITH AND BLUEJAY ONLY!
I would like to continue the discussion Faith began in The End of Evolution By Means of Natural Selection in the Great Debate forum, if she is interested in continuing it.
I’ll focus my comments on this portion of her OP there:
Faith writes:
But whether we are talking only about a change in a single trait or in many traits at once, the trend is ALWAYS toward genetic depletion. You can add as many new alleles as you think mutation can come up with at any point in this progression, but when these selection and isolating processes go to work on them the very same thing happens. You may get a new trait but you'll always get it at the expense of all the other genetic possibilities, and when this occurs with many traits you eventually get speciation, fixed loci, and such limited ability for further variation evolution is for all intents and purposes at an end.
This topic has caused a lot of frustration (primarily for Faith herself), so I’ll try to tread softly and take it easy. I’ll provide a basic comment on each sentence from the above quotation: these will serve as prompts that can be used by Faith to start her side of the discussion however she chooses.
Faith, please let me know what I may have misunderstood from your statements, and help me find if and where I'm off base on any or your points.
Faith writes:
But whether we are talking only about a change in a single trait or in many traits at once, the trend is ALWAYS toward genetic depletion.
I can only address this statement by appealing to mutation, which is known to happen at extremely higher rates than natural selection happens. If mutation is disallowed, then this statement may very well be quite true.
However, if mutation is allowed, then it becomes a question of comparing the rate of selection-mediated diversity loss to the rate of mutation-mediated diversity gain.
-----
Faith writes:
You can add as many new alleles as you think mutation can come up with at any point in this progression, but when these selection and isolating processes go to work on them the very same thing happens.
For this one, we need to consider a timeline of events, including the following events---
  1. Onset of selection pressure
  2. Emergence of new alleles
  3. Extermination of alleles selected against
---and, the following considerations---
  1. Other concurrent selection pressures
  2. Genetic linkage between different alleles
  3. Magnitude of each selection pressure
If we choose to pursue this complex model, I think we’ll quickly find that decreasing genetic diversity is not so inevitable as you have argued.
-----
Faith writes:
You may get a new trait but you'll always get it at the expense of all the other genetic possibilities, and when this occurs with many traits you eventually get speciation, fixed loci, and such limited ability for further variation evolution is for all intents and purposes at an end.
I explained a bit about genetic fixation in a few other places. Fixation is what you’re talking about: the elimination of all alleles for a certain gene except for one.
I do not think that fixation is inevitable, and I’m certain will never occur at all positions in the genomes of all individuals within a single population.
Selection pressures simply cannot be orchestrated such that any single organism can contain all the best alleles for all genes: so, naturally, we should expect that no single combination of alleles will be absolutely superior to all other possibilities in a population.
As an example, let me present Uta stansburiana, the rock-paper-scissors lizard I referred to earlier in your thread. This is an (admittedly unusual) example of a population that has reached a relatively stable balance between different genotypes. This sort of balancing act is what is going on in nearly all populations, all the time: the equilibrium oscillates between different character states, occasionally leading to the complete extinction of a certain trait, but also often leading to a complete rebound of a rare allele.
-----
I look forward to your responses, and I hope I won’t upset you and frustrate you too much in our discussion.

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

AdminSlev
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Message 2 of 2 (553179)
04-01-2010 7:10 PM


Thread Copied to The Great Debate Forum
Thread copied to the Reduction of Alleles by Natural Selection (Faith and ZenMonkey Only) thread in the The Great Debate forum, this copy of the thread has been closed.

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