Comments on: The Three Necessary and Sufficient Conditions of Natural Selection https://gregladen.com/blog/2022/04/20/the-three-necessary-and-suffic-2/ Thu, 14 Apr 2022 00:39:38 +0000 hourly 1 https://wordpress.org/?v=6.4.8 By: billnut https://gregladen.com/blog/2022/04/20/the-three-necessary-and-suffic-2/#comment-543116 Thu, 09 Dec 2010 20:02:27 +0000 http://scienceblogs.com/gregladen/2009/08/25/the-three-necessary-and-suffic-2/#comment-543116 “Natural selection is E (energy) temporarily constrained in an m (mass) format.
Period.”

Really, my chair is natural selection?

]]> By: Dov Henis https://gregladen.com/blog/2022/04/20/the-three-necessary-and-suffic-2/#comment-543115 Fri, 09 Apr 2010 05:33:35 +0000 http://scienceblogs.com/gregladen/2009/08/25/the-three-necessary-and-suffic-2/#comment-543115 Natural Selection
Beyond Historical Concepts

Natural selection is E (energy) temporarily constrained in an m (mass) format.
Period.

Dov Henis
(Comments From The 22nd Century)
03.2010 Updated Life Manifest
http://www.the-scientist.com/community/posts/list/54.page#5065
Cosmic Evolution Simplified
http://www.the-scientist.com/community/posts/list/240/122.page#4427
“Gravity Is The Monotheism Of The Cosmos”
http://www.the-scientist.com/community/posts/list/260/122.page#4887

]]> By: Jim Thomerson https://gregladen.com/blog/2022/04/20/the-three-necessary-and-suffic-2/#comment-543114 Sat, 29 Aug 2009 14:08:28 +0000 http://scienceblogs.com/gregladen/2009/08/25/the-three-necessary-and-suffic-2/#comment-543114 If we presume no human intervention, I would see Great Danes and Chiuahuas as having strong premating isolation and likely postmating isolation as well. Whether extinction would occur is speculative and irrelivant.

In the topminnows mentioned above, there is the fusion of two small acrocentrics to form one large metacentric. The hybrids have 44 chromosomes. In meiosis two little acrocentrics line up with each metacentric, and meiosis proceeds right along. Interestingly enough, there is a natural population with 44 chromosomes which is not the result of interspecific hybridization. I am pleased that colleagues are carrying on further investigation of these species.

]]> By: marcie https://gregladen.com/blog/2022/04/20/the-three-necessary-and-suffic-2/#comment-543113 Fri, 28 Aug 2009 21:43:34 +0000 http://scienceblogs.com/gregladen/2009/08/25/the-three-necessary-and-suffic-2/#comment-543113 Artificial insemination is a normal and regular practice
in certain breeds of dog where natural mating is difficult. My question was not about how nature prevents genetically compatible species from interbreeding. I want to know how genetic incompatibility developes. How do changes in chromosomes come about for example?

]]> By: Greg Laden https://gregladen.com/blog/2022/04/20/the-three-necessary-and-suffic-2/#comment-543112 Fri, 28 Aug 2009 21:00:25 +0000 http://scienceblogs.com/gregladen/2009/08/25/the-three-necessary-and-suffic-2/#comment-543112 Jim: one. But it would quickly go extinct depending on certain details.

Marcie: There are a lot of things that can make two populations unable to reproduce that can be genetic other than chromosome differences, but chromosome differences certainly could have more importance than we usually assign.

]]> By: Jim Thomerson https://gregladen.com/blog/2022/04/20/the-three-necessary-and-suffic-2/#comment-543111 Fri, 28 Aug 2009 20:05:40 +0000 http://scienceblogs.com/gregladen/2009/08/25/the-three-necessary-and-suffic-2/#comment-543111 With horses and donkeys it is a matter of number and make-up of chromosomes. This is not always the case. I crossed blackstripe topminnows (40 chromosomes) with blackspotted topminnows (48 chromosomes) and got fertile hybrids. There are sixteen known localities where these two species occur together. They produce a few hybrids, but there is no evidence of of nuclear gene introgression beyond the area where they are together.

Isolating mechanisms for species can be divided into premating and postmating. Basically the premating mechanisms keep them from trying and the post mating mechanisms keep them from succeeding. The basic idea here, which is not always true, is that individuals who hybridize have reduced fitness.

Suppose all canids except Great Danes and Chiuahuas became extinct. How many species of canids would be left? One or two?

]]> By: marcie https://gregladen.com/blog/2022/04/20/the-three-necessary-and-suffic-2/#comment-543110 Fri, 28 Aug 2009 19:36:45 +0000 http://scienceblogs.com/gregladen/2009/08/25/the-three-necessary-and-suffic-2/#comment-543110 What you are describing is selective breeding done by nature, not man. The problem is that selective breeding produces new breeds and varities but not new species. I am talking about species that can not interbreed with the parent species due to genetic incapatibility, not species that simply don’t for a variety of reasons. I think genetic incapatibility in closely related species must have something to do with changes in the chromosomes. I have been curious about this for a long time but a never had anyone to ask. So, how do these changes occur? How come horses and donkeys cannot produce fertile offspring, but all the very different looking dog breeds, wolves and coyotes can?

]]> By: Carl Bajema https://gregladen.com/blog/2022/04/20/the-three-necessary-and-suffic-2/#comment-543109 Fri, 28 Aug 2009 08:48:43 +0000 http://scienceblogs.com/gregladen/2009/08/25/the-three-necessary-and-suffic-2/#comment-543109 Science educators need a good scientific description of how selection operates in nature. What are the causes and consequences of evolutionary processes?
The following is my proposed scientific description of natural selection.

Charles Darwin (1859:62) used the metaphor â??Struggle for Existenceâ? to describe the ecological interactions that individual organisms have with (1) the physical conditions of their environment, (2) individuals of other species, and (3) individuals of the same species. These ecological interactions cause the natural (including sexual) selection of hereditary variations, that is, cause the selective survival of genes, the selective exponential multiplication of genes and the selective recombination of genes (via mate choice) that affect adaptations (designs) for survival and reproductive success each generation.
The adaptations we observe today are the product of natural selection operating on genetic variation produced by mutations, sampling error (genetic drift) and selective recombination (via mate choice) each generation over billions of generations.

Science educators need some kind of comprehensive description like this to help students better understand what processes cause adaptive evolution and its relationship to nonadaptive evolutionary processes. Evolution is the result of “chance and necessity” with necessity (selection) superimposed on chance every generation.
This is a proposal. There probably are better ways to summarize the causes and consequences of selection that also include interations with accidents–mutations and sampling error.

]]> By: Jim Thomerson https://gregladen.com/blog/2022/04/20/the-three-necessary-and-suffic-2/#comment-543108 Thu, 27 Aug 2009 21:37:52 +0000 http://scienceblogs.com/gregladen/2009/08/25/the-three-necessary-and-suffic-2/#comment-543108 One of my colleagues, a biochemist, claimed expertise on sickel cell anemia. She felt that we field biologists were operating on a lower level. Once I got interested in sickle cell, I followed it in the literature and was pleased to call her attention to articles she had not seen. Because my interests were broader than hers, I read literature which she did not see. Anyway, so long as one is not homozygous for sickle, it is pretty neat stuff.

]]> By: Hilary Miller https://gregladen.com/blog/2022/04/20/the-three-necessary-and-suffic-2/#comment-543107 Thu, 27 Aug 2009 17:16:38 +0000 http://scienceblogs.com/gregladen/2009/08/25/the-three-necessary-and-suffic-2/#comment-543107 [14] The term “elimination” does not mean “elimination from a population” .. it means elimination on a case by case basis, via selection on individuals.

Ah, there’s the discrepancy. I was taking your definition to mean on a population level (as thats how I tend to think about allele frequencies), not elimination of individuals with particular alleles. In that case I fully agree with your definition!

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