|
Author
|
Topic: John A. Davison: Is Evolution Finished?
|
Moderator
Administrator
Member # 1
|
posted 22. February 2004 22:47
Is Evolution Finished?*
by John A. Davison
Abstract: Few scientists question the reality of evolution. I assume, with the majority, that it has occurred. What else can be said concerning this most mysterious of all biological processes? There is little more of which one can be certain. No one knows how, or how many times, life has originated. The more we learn about the complexity of even the simplest living systems, the less likely becomes the probability that life originated by chance. You may notice that the last three sentences are presented in the past tense. As evolutionists we can be certain that life did originate in the distant past. We can also be certain that evolution occurred in the past. But what can we say about the present? Can we be certain that evolution is in progress today? In this essay I will present evidence that evolution is no longer in progress. Before I do, I will define what I mean by evolution so there will be no ambiguity with respect to my claims. I will use the term evolution to indicate macroevolution, by which I mean the appearance of new diploid species of plants or animals. I accept the physiological definition of species. Two forms that can produce a viable hybrid will be considered separate species if that hybrid proves to be sterile. This is the hard definition proposed by Dobzhansky and will suffice for my purposes.
*This paper will appear in a forthcoming issue of Rivista di Biologia
To read the entire paper, please click here.
IP: Logged
|
|
Salvador T. Cordova
Member
Member # 959
|
posted 03. March 2004 16:43
Dr. Davison,
I very much enjoyed reading your paper. After reading about your plight as a professor, many of us at ISCID are deeply grateful you were willing to follow your academic and scientific conscience in the face of strong disagreement. Several of us here at ISCID are very sympathetic to your views.
I look forward to reading anything else you will publish in regard to these matters.
Cordially,
Salvador T. Cordova
IP: Logged
|
|
nosivad
Member
Member # 767
|
posted 03. March 2004 19:51
Thank you very much Salvador. I hope your post will serve to "break the ice". I am anxious to defend my views with respect to the great mystery of organic evolution.
IP: Logged
|
|
Mohammed Safar
Member
Member # 1167
|
posted 04. March 2004 19:53
The evolution will not be finished. take into your consideretion my special opinionabout this topic> When we speak about evolution, we uninteniollay as I guess, means increasing in ....
Why we ignore the reduction in species as part of evolution process?
The reduction phenomena are apparent for most people and iy usualyy takes place due to the enfluence of poeple themselves.
forgive my poor english
IP: Logged
|
|
The Pixie
Member
Member # 548
|
posted 15. March 2004 07:28
You seem to be claiming that only non-sexual reproduction can lead to macro-evolution. If we assume common descent for the moment, this would require that every species that ever existed was capable of non-sexual reproduction or its immediate species-ancestor was. Of all the mammalian species that have ever existed (for example) a large majority must have been capable of non-sexual reproduction. So why did none of these species survive to the present day?
The Pixie
IP: Logged
|
|
nosivad
Member
Member # 767
|
posted 15. March 2004 11:02
Pixie - Thank you for reactivating this thread. I prefer the term presexual to asexual. I have explained why I think sexual reproduction prevails today. It is to PREVENT evolution and stabilize the species. The first meiotic division can generate a great deal of genetic diversity as I explained in the Manifesto. Most importantly, it can produce genetic and chromosomal homozygosity in a single cytological event starting with a single heterozygous structural alteration in any cell destined to become an oocyte. This follows from the universal property of the first meiotic division that the sister (identical) strands (chromosomes) always remain together. Sexual reproduction is an extraordinarily conservative mechanism which at best can produce varieties or, if you prefer, subspecies. It is also perfectly possible that the semi-meiotic mode and the sexual mode coexisted in the past and could do so again for all I know. In any event, the term asexual unfortunately suggests clonal reproduction which is certainly not a property of the semi-meiotic mode. As a matter of fact, as I and others have experimentally verified, the first meiotic division can, for certain loci, produce more heterozygosity that the theoretical maximum of 50% for the sexual mode. Again, for verification, I refer you to the Manifesto and the sources cited there, including the 1961 paper by myself in the Journal of Heredity. That experience was instrumental in leading me to the semi-meiotic hypothesis, although it took 23 years to crystallize in my mind. I am a slow learner but I have a very good memory. I hope this helps to answer your question and I thank you for your interest.
[ 15. March 2004, 11:04: Message edited by: nosivad ]
IP: Logged
|
|
nosivad
Member
Member # 767
|
posted 16. March 2004 10:32
Pixie - I neglected to respond to your question about why no creatures reproduce by the semi-meiotic mode today. There is one very clear example of extant semi-meiotic reproduction. It is precisely how certain flagellate protozoa in the genus Spirotrichosoma reproduce. In the words of L.R. Cleveland, who discovered these forms -
"Nuclear division of these polyploids can be seen very plainly, especially those with 4 rod-shaped chromosomes. Every division is exactly alike: synapsis in the prophase, followed by formation of tetrads, and movement of the chromosomes to the poles as dyads, i.e. every division is exactly like the first division in meiosis".
I have further elaborated on this in section IV-3 of the Manifesto. It is also perfectly possible that this reproductive mode may be going on even as we correspond. Our knowledge of the details of reproduction is limited to relatively few life forms and a single rare event can have enormous consequences. The significant and universal fact is that meiosis requires two steps. If the sole purpose of meiosis was to produce haploid gametes, it would most simply proceed as follows. The homologous chromosomes would synapse, undergo crossing over and then separate in a single reduction division. No life form produces gametes this way. What I have proposed, and still believe, is that in meiosis we are observing the historical sequence of cytological events, in which the first division, a perfectly normal form of diploid reproduction, had to temporally precede the second division. Once the second division became mandatory, sexual reproduction became equally mandatory as the only way to restore diploidy. When that took place macroevolution came to a standstill. It is also important to recognize that there is no universal cytogenetic means of either sex determination or sex expression, which further supports my conclusion that sex determining mechanisms have independently evolved many times. That represents a capsule view of the semi-meiotic hypothesis and my view of contemporary evolutionary stasis generally. I hope this helps.
IP: Logged
|
|
charlie d.
Member
Member # 159
|
posted 17. March 2004 10:47
quote:
nosivad:
It is also important to recognize that there is no universal cytogenetic means of either sex determination or sex expression, which further supports my conclusion that sex determining mechanisms have independently evolved many times.
So, does the fact that all mammals, as far as we know, use the same mechanism for sex determination (XY heterogametic, SRY gene-dependent) indicate that all mammals are derived from a single "semi-meiotic speciation" event (and therefore that all mammals are "varieties or, if you prefer, subspecies" of the same semi-meiotic super-species), or that all current mammalian species just happened to reivent the same exact mechanism for sex determination after they speciated semi-meiotically?
[ 17. March 2004, 10:50: Message edited by: charlie d. ]
IP: Logged
|
|
nosivad
Member
Member # 767
|
posted 17. March 2004 15:38
Certainly not, although it is interesting that all mammals do share the same site for germ cell origin in the endoderm of the allantois. Similarly, the ZW-ZZ system of all birds is correlated with a universal origin of the germ cells from the extraembryonic endoderm anterior and lateral to the head. In the reptiles there are various sources for the germ cells which also correlates with variable cytogenetic mechanisms for sex determination. These correlations are what led me to the conclusion that sex was a secondary development, independently evolved many times, as Vorontsov had suggested long ago. The strictly sexual (Mendelian) model for evolution would indicate a universal sex determining and sex expressing system. Such is certainly not the case. While a universal molecular basis for sex determination may well be the case (I am far from convinced of that), the cytogenetic manifestation of that basis is certainly far from universal. The most significant feature of meiosis remains the indisputable fact that it occurs in two discrete steps, the first of which has been experimentally proven to be capable of producing fertile offspring of both sexes. To answer your question more directly, it is perfectly reasonable that in the past, and even now, animals might be able to reproduce both semi-meiotically and sexually as I indicated in an earlier post. It is unfortunate that the semi-meiotic hypothesis remains untested as the means are available in common amphibian material. I can only wonder why this is not being attempted. Perhaps it is for the same reasons the Darwinians stopped testing their own hypothesis. After all, Darwinism never was an experimental science. There is no point in testing something that just HAS to be true. Pardon my cynicism. It has developed over the years.
IP: Logged
|
|
charlie d.
Member
Member # 159
|
posted 17. March 2004 19:55
Actually, I don't think you have answered my question at all. Let me rephrase it. Do all mammalian species share the same mechanism for sex determination because:
a) they are all derived from the same "semi-meiotic species" (and therefore all mammalian groups are subspecies or variants thereof)?
or
b) they happened to re-evolve the same exact mechanism of sex determination after each and every one of their own unique "semi-meiotic" speciation events?
I don't think there are oher possibilities, are there?
As for empirical testing, I seem to remember you were on the faculty at UV for over a decade after you formulated the semi-meiotic hypothesis. Have you conducted any test of it? If so, what were the results, and where were they published? If not, why not?
IP: Logged
|
|
nosivad
Member
Member # 767
|
posted 17. March 2004 23:42
Charlie d. As I understand your question, you are asking me if there has been a single origin of the mammalian line. I don't know. The mammals and the birds may very well have had several different origins from separate reptilian ancestors. The same can be said for any other group. The Darwinian view has always favored a monophyletic origin for evolution generally, although there is no way for that to be substantiated. As I indicated in this paper, we have no idea how many times life has originated and we are equally ignorant of how it originated. As for your question about my activities after the 1984 paper, I will only tell you that, for reasons entirely beyond my control, I was unable to test the semi-meiotic hypothesis. That is the primary reason I have concentrated on the theoretical aspects of the evolutionary problem. I don't intend to further characterize my unfortunate experience with the administration of the University of Vermont. The reality is that I could not, and accordingly, did not test the semi-meiotic hypothesis and it remains untested twenty years later. I can only speculate, as I have, about the reasons. I am sure that you, like myself, realize how very little we really know for certain about the cytogenetic events that were responsible (past tense) for macroevolution, a process which I no longer see in operation. The semi-meiotic hypothesis recognizes this inadequacy and offers an opportunity to pursue what I regard as a potentially rewarding line of experimental inquiry. If you, or anyone for that matter, is satisfied with the Darwinian sexual model there is little I can do to dissuade you. I regard it as completely without foundation and, having published that conclusion, have joined with the six to whom I have dedicated my efforts, and on whose insights my own work so firmly rests. In any event, the truth will out.
[ 18. March 2004, 00:00: Message edited by: nosivad ]
IP: Logged
|
|
charlie d.
Member
Member # 159
|
posted 18. March 2004 08:03
quote:
nosivad:
Charlie d. As I understand your question, you are asking me if there has been a single origin of the mammalian line.
No, that's not what I asked. You said that according to the semi-meiotic hypothesis sexual reproduction has to be reinvented every time after a semi-meiotic speciation event. I asked therefore if existing mammalian species, which all use the same sex determination mechanism, are all derived from the same semi-meiotic speciation event (and are all therefore, semi-meiotically speaking, sub-species), or if they all rediscovered sex in the same identical manner after each and every semi-meiotic speciation event (however many you envision). That's a fairly straightforward question.
As for the testing, I am not sure what UV could have done about what you chose to do with your own time in your own lab - I would imagine, nothing. As far as I know they got upset at you for teaching students a view which is currently (as was then) held by a single biologist in the world (you), and neglecting to teach them the scientific consensus which they had paid to learn. Frankly, that seems like a reasonable position to me, as far as required courses go (of course, any faculty should be allowed to teach whatever they want in elective courses, from the semi-meiotic hypothesis to belly-dancing, provided the content is fairly outlined beforehand)
Anyway, back to the test: what exactly does it imply, experimentally? Don't wax philosophical, give me an experimental plan: aims, design and methods, expected results.
IP: Logged
|
|
nosivad
Member
Member # 767
|
posted 18. March 2004 11:12
charlie d. I don't care for your tone or innuendo. As for what I presented in the classroom, it was balanced and objective I can assure you. That is precisely why I was treated the way I was. You ask about the test for the semi-meiotic hypothesis. It is clearly spelled out in the Manifesto and is based on the experimental methods employed by Nace, Hertwig, Loeb and other developmental biologists, including myself. Here is one variant on a number of potential possible tests. Ovulating female frogs have their eggs experimentally activated with heavily irradiated sperm. Such sperm contribute no genetic information and if nothing else is done the eggs will develop into haploids all of which fail to reach adulthood. To prevent the second meiotic division from taking place, the eggs can be heated briefly to prevent the second meiotic division. Such eggs develop into normal diploid animals of BOTH sexes. Any oogonial line which has undergone a structural rearrangement in any chromosome will produce two karyotype homozygotes in equal frequency, the original wild type karyotype and a new homozygous karyotype, in principle a new species produced instantly without intermediates. Of course this explanation would be quite unnecessary for anyone with even a passing understanding of vertebrate oogenesis and meiosis, especially since I have already presented this material in my Manifesto and published papers, material which you have obviously either not read or not comprehended, I cannot tell which. I hope this serves to answer your question. I also note, completely ignorant of the academic scene at the University of Vermont, your remarkable interpretation of what constitutes academic freedom. For me to continue to support the Darwinian myth in any form would be intellectually criminal. I will be happy to respond to any further questions provided only that they be presented in a civilized fashion. Otherwise I will simply refer to published findings and let the inquisitors find it out for themselves as I have done. To paraphrase an old saw -
"You can lead a man to the literature but you cannot make him read (or comprehend) it."
[ 18. March 2004, 11:19: Message edited by: nosivad ]
IP: Logged
|
|
Paul Lucas
Member
Member # 365
|
posted 19. March 2004 10:51
Novisdad said "we have no idea how many times life has originated and we are equally ignorant of how it originated. "
It is true that we have no idea how many times life has originated. Because of the identity of the genetic code amongst organisms, the hypothesis is that all organisms on the planet came from a common ancestor no matter how many times life has originated.
Data now indicate the life is still originating at hydrothermal vents. Of course, it comes into existence in the presence of life that has existed for 3.8 billion years and that life looks at the new life and yells "LUNCH".
However, there is an abundant literature on how life can come from non-life and, by the definition of life, life has already been generated from non-life. Some literature for you to read is:
4. SW Fox, Synthesis of life in the lab? Defining a protoliving system. Quarterly Review of Biology, 66: 181-185, 1991.
Protocells under prebiotic conditions:
Snyder WD and Fox, SW. A model for the origin of stable protocells in a primitive alkaline ocean. BioSystems 7: 222-229, 1975.
Rohlfing, DL. Thermal polyamino acids: synthesis at less than 100°C. Science 193: 68-70, 1976.
Syren RM, Sanjur A, Fox SW Proteinoid microspheres more stable in hot than in cold water. Biosystems 1985;17(4):275-80 (protocells at hydrothermal vents)
Yanagawa, H. and K. Kobayashi. 1992. An experimental approach to chemical evolution in submarine hydrothermal. systems. Origins of Life and Evolution of the Biosphere 22: 147-159.
Marshall, W. H. 1994. Hydrothermal synthesis of amino acids. Goechimica et Cosmochimica Acta 58: 2099-2106.
McAlhaney WW, Rohlfing DL. Formation of proteinoid microspheres under simulated prebiotic atmospheres and individual gases. Biosystems 1976 Jul;8(2):45-50
Fouche-CE Jr; Rohlfing-DL Thermal polymerization of amino acids under various atmospheres or at low pressures. Biosystems. 1976 Jul; 8(2): 57-65
SW Fox, Thermal polymerization of amino-acids and production of formed microparticles on lava. Nature, 201: 336-337, Jan. 25, 1964.
Hennon, G, Plaquet, R, Biserte, G. The synthesis of amino acid polymers by thermal condensation at 105° without a catalyst. Biochimie 57: 1395-1396, 1975.
Heinz, B, Reid, W. The formation of chromophores through amino acid thermolysis and their possible role as prebiotic photoreceptors. BioSystems 14: 33-40, 1981.
Structure and internal ordering:
Turcotte, PA, Paolillo, L, Ferrara, L, Benedetti, E, Andini, S. Structural characterization of thermal prebiotic polypeptides. J. Mol. Evol. 7: 105-110, 1976.
Rohlfing, DL. Thermal poly-a-amino acids containing low proportions of aspartic acid. Nature 216: 657-659, 1967.
Tyagi S, Ponnamperuma C Nonrandomness in prebiotic peptide synthesis. J Mol Evol 1990 May;30(5):391-9
Melius P. Structure of thermal polymers of amino acids. Biosystems 1982;15(4):275-80 Jul;8(2):45-50
SW Fox, Stereomolecular interactions and microsystems in experimental protobiogenesis. BioSystems 7: 22-36, 1975
SW Fox, Self-sequencing of amino acids and origins of polyfunctional protocells. Origins of Life, 14: 485-488, 1984.
Temussi, PA, Paolillo, L, Ferrara, L, Benedetti, I, Aninin, S. Structural characterization of thermal prebiotic polypeptides. J. Mol. Evol. 7: 105-110, 1976.
Pivcova, H, Saudek, V, Drobnik, J, Vlasak, J. NMR study of poly (aspartic acid) I. a- and b-peptide bonds in poly(aspartic acid) prepared by thermal polycondensation. Biopolymers 20: 1605-1614, 1981.
Nakashima, T, Jungck, JR, Fox, SW, Lederer, E, Das, BC. A test for randomness in peptides isolated from a thermal polyamino acid. Intl. J. Quantum Chem. QBS4: 65-72, 1977.
Luque-Romero MM, de Medina LS, Blanco JM. Fractionation and amino acid composition of an aspartic acid-containing thermal proteinoid population. Biosystems. 1986;19(4):267-72.
Bahn, P. and A. Pappelis. 2001. HPLC evidence of nonrandomness in thermal proteins. In First Steps in the Origin of Life in the Universe. Julián Chela-Flores, Tobias Owen, and François Raulin, eds., Kluwer Academic Publishers, Dordrecht, The Netherlands. Pp. 69-72.
Bahn, P. and A. Pappelis. 2001. IR spectra of protein, thermal protein, and thermal glycoprotein. In First Steps in the Origin of Life in the Universe. Julián Chela-Flores, Tobias Owen, and François Raulin, eds., Kluwer Academic Publishers, Dordrecht, The Netherlands. Pp.73-76.
Thermal proteins from DL and nonproteinous amino acids
Saunders MA and Rohlfing DL, Inclusion of nonproteinous amino acids in thermally prepared models for prebiotic protein. Biosystems 6. 81-92, 1974.
Metabolism:
Rohlfing, DL, Fox, SW. Catalytic activities of thermal polyanhydro-a-amino acids. Advances Catal. 20: 373-418, 1969.
Hydrolysis (energy gaining):
p-nitrophenyl acetate
Fox, S., Harada, K. Rohlfing, DL The thermal copolymerization of a-amino acids. In Stahmann, MA (ed) Polyamino Acids, Polypeptides, and Proteins (Univ. of Wisconsin Press, Madison) 47-54, 1962
Rohlfing DL and Fox, SW. The catalytic activity of thermal polyanhydro-a-amino acids for the hydrolysis of p-nitrophenyl acetate. Arch. Biochem. Biophys. 118: 127-132, 1967.
Usdin, VR, Mitz, MA, Killos, PJ. Inhibition and reactivation of the catalytic activity of a thermal a-amino acid copolymer. Arch. Biochem. Biophys. 122: 258-261, 1967.
p-nitrophenyl phosphate
Oshima, T. The catalytic hydrolysis of phosphate ester bonds by thermal polymers of amino acid. Arch. Biochim. Biophys. 126: 478-485, 1968.
Decarboxylation
Glururonic acid: Fox, SW and Krampitz, G. The catalytic decomposition of glucose in aqueous solution by thermal proteinoids. Nature 203: 1362-134, 1964
Pyruvic acid: Hardebeck, HG, Krampitz, G, Wulf, L. Decarboxylation of pyruvic acid in aqueous solution by thermal proteinoids. Arch. Biochem. Biophys. 123: 72-81, 1986.
Oxaloacetic acid: Rohlfing, DL THe catalytic decarboxylation of oxaloacetic acid by thermally prepared poly-a-aminoacids. ARch. biochem. Biophys. 118: 468-474, 1967.
Deamination
Krampitz, G, Haas, W. Baas-Diehl, S. Glutaminsaure-Oxydoreductase-Aktivitat von polyanhydro-a-aminosauren (proteinoiden). Naturwissenschaften 55: 345-346, 1968.
Anabolism:
Amination: Krampitz, g, Baars-Diehl,S, Haas, W, Nakashima,T. Aminotransferase activity of thermal polylysine. Experientia 24: 140-142, 1968.
Kolesnikov, M.P. 1991. Proteinoid microspheres and the process of prebiological, photophosphorylation. Origins of Life and Evolution of the Biosphere 21: 31-37. ADP + Pi + light yields ATP
RNA/DNA: JR Jungck and SW Fox, Synthesis of oligonucleotides by proteinoid microspheres acting on ATP. Naturwissenschaften, 60: 425-427, 1973.
Peptides:
T Nakashima and SW Fox, Synthesis of peptides from amino acids and ATP with lysine rich proteinoid. J. Mol. Evol. 15: 161-168. 1980.
Fox, SW, Jungck, JR, Nakashima, T. From proteinoid microsphere to contemporary cell: formation of internucleotide and peptide bonds by proteinoid particles. Origins of Life 5: 227-237, 1974.
Nakashima, T, Fox, SW. Formation of peptides by single or multiple additions of ATP to suspensions of nucleoproteinoid microparticles. BioSystems 14: 151-161, 1981.
Paecht-Horowitz M, Katchalsky A. J Synthesis of amino acyl-adenylates under prebiotic conditions. Mol Evol 1973;2(2-3):91-8
Oxidoreductions: H2O2 (catalase) and H2O2 and hydrogen donors (peroxidase reaction)
Dose, K, Zaki,L. The peroxidatic and catalase activity of hemoproteinoids. Z. Naterforsch 26b: 144-148, 1971.
Photoactivated decarboxylation -- glycoxylic acid, glucuronic acid, pyruvic acid.
Wood, A, Hardebeck, HG. Light-enhanced decarboxylations by proteinoids. In Rohlfing, DL and Oparin, AI (eds) Molecular Evolution (Plenum, New York), 233-245, 1972.
Hormone: Fox, SW, Wang, C-t. Melanocyte-stimulating hormone activity in in thermal proteins of a-amino acids. Science 160: 547-548, 1968.
Compartments within protocells:
Brooke S, Fox SW. Compartmentalization in proteinoid microspheres.Biosystems. 1977 Jun;9(1):1-22.
Photosynthesis:
Bahn PR, Fox SW. Models for protocellular photophosphorylation. Biosystems. 1981;14(1):3-14.
Masinovsky Z, Lozovaya GI, Sivash AA, Drasner M. Porphyrin-proteinoid complexes as models of prebiotic photosensitizers. Biosystems 1989;22(4):305-10.
Masinovsky Z, Lozovaya GI, Sivash AA. Some aspects of the early evolution of photosynthesis. Adv Space Res 1992;12(4):199-205.
Response to stimuli
Przybylski AT. Excitable cell made of thermal proteinoids. Biosystems 1985;17(4):281-288.
Vaughan G, Przybylski AT, Fox SW. Thermal proteinoids as excitability-inducing materials. Biosystems. 1987;20(3):219-23.
Ishima Y, Przybylski AT, Fox SW. Electrical membrane phenomena in spherules from proteinoid and lecithin. Biosystems. 1981;13(4):243-51.
Pappelis, A., S. W. Fox, R. Grubbs, and J. Bozzola. 1998. Animate protocells from inanimate thermal proteins: Visualization of the Process. In Exobiology: Matter, Energy, and Information in the Origin and Evolution of Life in the Universe. J. Chela-Flores and F. Raulin, eds., Kluwer Academic Publishers, Dordrecht, The Netherlands, Pp.195-198.
Growth and Reproduction:
Fox, SW, McCauley, RJ, Wood, A A model of primitive heterotrophic proliferation. Comp. Biochem. Physiol. 20: 773-778, 1967.
Fox, SW. Molecular evolution to the first cells. Pure Appld. Chem. 34: 641-669, 1973.
Communication:
Hsu, LL, Brooke, S, Fox, SW. Conjugation of proteinoid microspheres: a model of primordial communication. Curr. Mod. Biol. (now BioSystems) 4: 12-25, 1971.
Protocells as units of evolutionary selection:
Matsuno K Natural self-organization of polynucleotides and polypeptides in protobiogenesis: appearance of a protohypercycle. Biosystems 1982;15(1):1-11
Kenyon, DH. Prefigured ordering and protoselection in the origin of life. In Dose, K, Fox, SW, Deborin, GA, and Pavlovskaya, TE (eds) The Origins of Life and Evolutionary Biochemistry (Plenum Press, New York), 207-220, 1974.
Fox SW. Molecular selection and natural selection. Q Rev Biol. 1986 Sep;61(3):375-86.
Beginnings of genetic code:
Nakashima T, Fox SW. Selective condensation of aminoacyl adenylates by nucleoproteinoidmicroparticles (prebiotic-lysine-model system-genetic code).Proc Natl Acad Sci U S A. 1972 Jan;69(1):106-8.
Yuki A, Fox SW. Selective formation of particles by binding of pyrimidine polyribonucleotides orpurine polyribonucleotides with lysine-rich or arginine-rich proteinoids.Biochem Biophys Res Commun. 1969 Aug 15;36(4):656-63.
Protocells as new domain of life
Pappelis A, Fox SW. Domain Protolife. Journal of Biological Physics 20: 129-132, 1994.
http://www.asa3.org/archive/evolution/199907/0062.html
IP: Logged
|
|
Paul Lucas
Member
Member # 365
|
posted 19. March 2004 11:07
Novisad said "Sexual reproduction is an extraordinarily conservative mechanism which at best can produce varieties or, if you prefer, subspecies."
Sexual reproduction, by itself, does not produce a new species. It is natural selection selecting among the variations among individuals in a population that shifts, over generations, the alleles in the population such that the population is no longer the same species as the original.
As you say, sexual reproduction acts in two ways. One is conservative in combining maladaptive recessives into a single individual such that the recessives are then eliminated from the population. But the other is progressuve by producing greater variation in the population than can be produced by asexual reproduction. Asexual reproduction relies solely on mutation to produce variation since all offspring are clones. Sexual reproduction, however, introduces recombination where new combinations of alleles can be generated. Since most traits are polygenic, this provides more variations for selection to choose among. Thus, favorable variations for a particular environment can be generated by a combination of alleles without waiting for a new mutation.
As the reference list noted, the generation of new species in diploid organisms have been observed in both the lab and the wild. In terms of hybrid sterility, that depends on mutations in a particular cassette of genes. That cassette has now been identified.
1. M Nei and J Zhang, Evolution: molecular origin of species. Science 282: 1428-1429, Nov. 20, 1998. Primary article is: CT Ting, SC Tsaur, ML We, and CE Wu, A rapidly evolving homeobox at the site of a hybrid sterility gene. Science 282: 1501-1504, Nov. 20, 1998. As the title implies, has found the genes that actually change during reproductive isolation.
So, hybrid sterility -- one marker on the road to speciation -- is not a result of sexual reproduction, but mutational changes in a homeobox gene.
Finally, your defintion of "macroevolution" makes use of Dobzhansky's biological species concept. That concept is:
"A species is a group of individuals fully fertile inter se, but barred from interbreeding with other similar groups by its physiological properties. (producing either incompatibility of parents, or sterility of the hybrids, or both). (Dobzhansky 1935) " Evolutionary Biology, 3rd ed., by Douglas Futuyma, table 15.1 page 448
You used only sterility of hybrids, but Dobzhansky also stated bluntly that incompatibility of parents was also sufficient for a new species. If the members of two populations do NOT breed when in contact, for whatever reason, you have two species.
IP: Logged
|
|
|
Topic Closed
Printer-friendly view of this topic
