mark kennedy said:
Baloney! Natural Selection simply makes extinct the species or subspecies that is less fit. It is based on Maltusian geometric growth of populations and it is a mechanism for extinction by definition.
Natural selection works on
individuals, not on species or subspecies. What natural selection does is pick the
individuals with the best design for the situation. As you noted. Matthusian geometric growth itself guarantees that a lot of individuals are going to die. There are simply too many individuals for the limited resources to support. So the death of individuals has nothing to do with natural selection -- instead natural selection picks the individuals with the best designs and then, by inheritance, insures that those designs are passed to the next generation.
How? How are these characterizations produced? That is the question and you have no demonstratable mechanism for that.
Hmm, you changed the claim. Your first claim was that natural selection was "extinction". I used Darwin to point out to you that NS is
preservation. Well, you are not arguing that, but have switched claims. So I guess we can conclude that NS is preservation and not extinction. Your first claim is abandoned.
Now, as to your
new claim -- "how are these characterizations produced" -- the answer is in the first sentence:
If, during the long course of ages and under varying conditions of life, organic beings vary at all in the several parts of their organization, and I think this cannot be disputed; Those variations return as "But if variations useful to any organic being do occur, assuredly individuals thus characterized "
You know full well how the variations/characterizations are produced.
1. Sexual recombination.
2. Mutation.
Natural selection has
two components.
Both have to be present.
1. Variation.
2. Selection. As you noted, Malthusian geometric proliferation ensures that more offsrping are produced than can survive to reproduce. Thus, there
must be selection among all the members of the population for those that will survive and reproduce. The selection is done in the metaphorical Struggle for Existence, which Darwin and others have documented. The competition for those scarce resources. Individuals with the better designs will get the resources in the competition. Thus they will survive and reproduce, passing the good designs to the next generation.
I read your divisionary tactic and it doesnt provide a mechanism for this mythical monstrocity or address the issue of evolution during the cleavage stage.
I knew you wern't honest enough to read the material, but I hoped anyway.
What you are doing is looking at the physical results of cleavage and saying "there must be homology in the structure of cleaved blastocyst. Since there is no homology of structure, there is no homology". What developmental biologists are looking at are the genes that control the process and saying there is homology in the genes!
"HOMOLOGIES OF PROCESS
It is well established that certain structures are homologous. These include things like the arm of a human and the flipper of a seal and the eing of a bird. They are constructed from the same basic elements arranged in a similar manner. It is also well established that molecules can be homologous. Thus, the globin proteins or genes of humans are homologous to those of a horse or a bat. Homology indicates a similarity established through common descent. ...
"There is now evidence that certain developmental pathways are themselves homologous both within an organism and between phyla. This goes beyond the several developmental regulatory genes (
Pax6, finge, tinman, the Hox genes) that have been found to be extremely well conserved throughout animal evolution (see Gilbert, 1997). ...
However, whereas the structure and expression pattern of one set of genes may not be an indication of homology, the coordinated assembly of several genes and gene products into functional cassettes does indicate homologous relationships if these casettes are shared between species or between tissues within an organism. Here we see that pathways can be homologous, and we get into a new understanding of homology: the homology of process."
http://zygote.swarthmore.edu/evo7.html
Thus, the homology of cleavage is not homology of the structure of the cleaved blastocyst, but homology of the functional cassette of genes that controls the process of cleavage.
I knew you were unable to address this issue but I decided to remove you from the ignore list to see if you addressed the issue at hand. Here is the issue at hand, think about it before you respond:
"Given the hierarchical, step-wise logic or "architecture" of animal development, early stages such as cleavage and gastrulation lay the groundwork for all that follows... How then did these different starting points evolve from a common ancestor? "
You are in uncharted waters here, don't bother with the liniks, they can't help you here.
No, the waters aren't uncharted. Just unread by
you! I suggest you take your own advice and "actually reading the source material before you ramble on". Go to the source material and see if you can use that to refute the above. Good luck.
"
1. The Hedgehog-Wnt pathway
The concept of process homology can be traced to the observations of Howard Schneiderman. He observed homologous specification--the phenomena wherein transdifferentiating cells or the products of homeotic gene mutations have a pre-existing positional information relevant to where they reside in the imaginal disc. A piece of antenna tissue that differentiates as a leg will differentiate according to its location in the antennal disc. Schneiderman's observations (see Postlethwait and Schneiderman, 1971) were particularly important because they helped show that homology had to be defined at a particular level. Structures with no anatomical homology--the eye and the leg--may have an underlying homology of process. Hense his term, homologous specification. We are now becoming aware of the process homology that unites the eye, the wing, and the leg discs. It is the hedgehog/Wnt pathway. These two paracrine factors interact within the disc to specify the proximal/distal, dorsal/ventral, and anterior/posterior axes. The same molecules that specify these axes in the eye also specify them in the leg and wing discs. So we have a serial process homology. Moreover, the same pathway exists in vertebrates. Every member of the pathway in insects has a homologue in the vertebrate embryo, and the same interactions that transmit the Drosophila Wingless signal to the nucleus through armadillo and pangolin protein are seen in the vertebrates, wherein the Wnt signal is manifest in the entry of beta-catenin and Lef-1 into the nucleus. The genes are the same and the protein interactions are the same. Only the readout is changed from tissue to tissue and from species to species. Interestingly, the same Wnt/hedgehog interactions seen in producing the fly limbs are seen in the interactions that are involved in the morphogenesis of vertebrate limbs. If a vertebrate hedgehog protein (which is usually synthesized only in the posterior mesoderm) is expressed anteriorly, the limb develops a mirror-image duplication. This is the same phenomenon that occurs when hedgehog protein is induced to form in the anterior portion of the fly wing disc (see Ingham, 1994). " http://zygote.swarthmore.edu/evo7.html
"
Most discussions of homology have not discussed processes as being homologous. This is to be expected, since evolutionary biology and systematics has been predominantly a study of adult structures. But if homologies are to be observed in the embryo, they shouldbe homologies of processes, not structures. It was C. H. Waddington who emphasized the importance of processes. As Waddington (1975) wrote:
As far as scientific practice is concerned, the lessons to be learned from Whitehead were not so much derived from his discussions of experiences, but rather from his replacement of "things" by processes which have an individual character which depends upon the "concrescence" into a unity of very many relations with other processes."
In terms of embryos, Waddington envisioned the concrescences of numerous genes and their products into a stabilized pathways. These developmental pathways were real "things", and they were subject to natural selection. Whitehead was much respected by the embryologists of the 1930s because he viewed the concept of "becoming" as superior to that of "being." As Whitehead (1933) viewed reality, "the very essence of actual reality--that is, of the completely real--is process. Thus each actual thing is only to be understood in terms of its becoming and perishing...The process is itself the actuality..." Today, we are extending Waddington's Whiteheadian notion that developmental pathways are themselves real and selectable things by noting that like "things"--limbs, ribs, wings, nucleotide sequences, amino acid sequences--they can be homologous both within and between organisms. "
