All, I think this question is important, in that apparently there are a variety of opinions out there as to what Natural Selection does and does not. In all this discussion, nobody that believes NS favors extinction has put NS into a logical framework (premises, assumptions, - basically, a syllogism) that would explain the process. AND, it seems to me that most that opine that NS favors extinction, seem also to think that extinction only occurs by "evolution by NS."
I would say that extinction can occur for many reasons that have nothing to do with natural selection. In today's world, habitat loss, disease, exploitation, and so on. Probably was true in the past as well. It is not true that every extinction was the result of a struggle between a winning species and a losing species. The syllogism that best explains (in my book) NS is the following: IF 1. Individuals vary phenotypically for some trait or traits, AND 2. Those traits are due to genotypic variability, AND 3. Fitness is associated with those phenotypic trait or traits, THEN, Individuals with the trait associated with greater fitness will leave MORE genes of that phenotypic trait in subsequent generations. Ergo, Natural Selection. If conditions favor that same process for many generations, we are likely to have evolution by natural selection. And, remember, phenotypic variation may be only environmental. Now, I would say, with this syllogism, just like the expression "SH__ HAPPENS" we can say "extinction happens" with or without natural selection. . Finally, we can think of evolution by natural selection as a process that generates adaptations. Adaptations are advantages given a certain set of environmental circumstances. Sure, adaptations in the wrong circumstances can become hindrances, but natural selection did not "make" them to hinder the organism. Rather circumstances changed (Ice Age, for example). Difficult to imagine natural selection favoring a maladaptation.... Fitness is defined as differential reproductive success, not natural selection. Cheers, Jim Jane Shevtsov wrote: > Imagine a stable population in which a favorable new genotype has > appeared and is increasing. That sure looks like selection FOR the new > genotype to me. On the other hand, if we start with the same > population and change the environment so some of the old genotypes no > longer do well, I'd call that selection AGAINST those genotypes. > > This is all just semantics. If confused, stick to "differential > reproduction". > > Jane > > At 07:16 AM 7/13/2006, Malcolm McCallum wrote: >> Am I understanding you correct? =20 >> Natural Selection selects against unfavorable phenotypes. >> Sexual Selection selects for favorable phenotypes. >> =20 >> =20 >> =20 >> VISIT HERPETOLOGICAL CONSERVATION AND BIOLOGY www.herpconbio.org = >> <http://www.herpconbio.org>=20 >> A New Journal Published in Partnership with Partners in Amphibian and = >> Reptile Conservation >> and the World Congress of Herpetology. >> =20 >> Malcolm L. McCallum >> Assistant Professor >> Department of Biological Sciences >> Texas A&M University Texarkana >> 2600 Robison Rd. >> Texarkana, TX 75501 >> O: 1-903-223-3134 >> H: 1-903-791-3843 >> Homepage: https://www.eagle.tamut.edu/faculty/mmccallum/index.html >> =20 >> >> ________________________________ >> >> From: Ecological Society of America: grants, jobs, news on behalf of = >> James J. Roper >> Sent: Thu 7/13/2006 6:37 AM >> To: [email protected] >> Subject: Re: Maldaptation, Extinction and Natural selection >> >> >> >> But Wirt, >> >> Natural selection doesn't "cull" but rather it "favors." And selecting >> "for" something is very different than selecting "against" something.=20 >> Favoring a trait leads to adaptation. That is, those with a trait leave >> more descendents. Even so, it is not that simple. At any rate, John >> Endler does a wonderful job of clearing things up with "Natural >> Selection in the Wild" and I highly recommend it for anyone who has not >> read it, and, don't forget, "The Extended Phenotype" by Dawkins, that >> should also be required reading. >> >> > Interpreting literally what I wrote leads to a condition that I = >> normally rail >> > against myself. Selection never selects "for" anything. Selection = >> operates >> > only as a culling mechanism, removing the least appropriate, least = >> competitive >> > phenotypes of the demic excess that currently fills the competitive = >> arena. >> > =20 >> What the heck does "demic excess" really mean? >> >> Cheers, >> >> Jim > > ================================================================================================== > > > "The whole person must have both the humility to nurture the Earth and > the pride to go to Mars." --Wyn Wachhorst, The Dream of Spaceflight > > Jane Shevtsov > co-founder, <http://www.worldbeyondborders.org/>World Beyond Borders > visit my blog, <http://perceivingwholes.blogspot.com/>Perceiving Wholes > > "Perhaps one day... the world, our world, won't be upside down, and > then any newborn human being will be welcome. Saying, "Welcome. Come. > Come in. Enter. The entire earth will be your kingdom. Your legs will > be your passport, valid forever."" --Eduardo Galeano, Latin American > writer > -- ------------------------------------- James J. Roper, Ph.D. Universidade Federal do Paraná Depto. de Zoologia Caixa Postal 19020 81531-990 Curitiba, Paraná, Brasil ===================================== E-mail: [EMAIL PROTECTED] Phone/Fone/Teléfono: 55 41 33611764 celular: 55 41 99870543 e-fax: 1-206-202-0173 (in the USA) ===================================== Zoologia na UFPR http://www.bio.ufpr.br/zoologia/ Ecologia e Conservação na UFPR http://www.bio.ufpr.br/ecologia/ ------------------------------------- http://jjroper.sites.uol.com.br
