by susu.exp wrote:A few quibbles:Calilasseia wrote:Plus, if you're about to erect the fatuous "no transitional fossils exist" creationist canard, then you really do need to go back to school and re-learn science from the ground up. Not least because, in case you hadn't worked this out, every living organism is a transitional form between its parents and its offspring.
That´s bollocks. Not because it´s wrong per se, but because it doesn´t use the technical definition of transitional form. A transitional form is an organism, extinct or extant, that allows us to infer something about the sequence of character evolution. We know that the plesiomorphic state for synapsids was hairless and laid amniote eggs. We know that placentalia have hair and give live birth. The duck billed platypus is a transitional form, because it tells us that hair evolved before vivipary. Being transitional is not a property of an organism, it´s a property of an organism discovered at some point of our study. If we found a new species of basal mammals showing the same set of symplesiomorphies that the platypus shows, it wouldn´t be transitional, because it wouldn´t tell us anything new about character evolution.
Transitional fossils are something else entirely. A gap in the fossil record is the time span between the first appearance of a clade and its sister clade. A transitional fossil is one that reduces such a gap, i.e. a fossil belonging to the clade with the younger first appearance date, leading to a new first appearance date, that is closer to the first appearance date of the sister clade. Tiktaalik is a good example (even though tetrapod tracks now have increased the gap again - tetrapods now have a first appearance date older than their sister group). Between the first appearance of the tetrapod sister group and the first appearance of tetrapods there was a temporal gap of 20Ma IIRC. Tiktaalik extended the range of tetrapods back 10Ma, shrinking the gap to 10Ma.
Being a transitional fossil landed Tiktaalik the Nature cover. If every species was transitional, it wouldn´t have been something special and presumably not even been published by Nature, much less pubished as the cover.
First of all, I bow of course to your superior knowledge in this field. Polanyi, take note, susu engages in research in this field as part of his professional remit, which means [1] he knows what he's talking about, and [2] I'm not going to display the epic level of stupidity required to try and tell him he's wrong.
However, the point I was striving to make was this. The accumulation of small differences from one generation to the next produces the very features you have described above. Dissemination of variation across generations is the mechanism that underpins this. The only reason that transitional forms are regarded as 'special' in scientific work is because we don't have the vast collection of physical data stretching across the thousands of generations in the case of fossil organisms.What we do have, though, is hard evidence from living organisms that new features can arise in accordance with evolutionary mechanisms, and as a consequence of this, we may safely infer that the same mechanisms applied to organisms in the past, given that the inheritance mechanisms generating this are the only mechanisms we have hard evidence for to produce the observed features. It is only because the fossil record forces us to work with incomplete samples of those past organisms, that the whole 'transitional form' business is regarded as 'special' - if we had access to complete physical data for the respective lineages, transitional forms wouldn't be 'special' at all, they'd be trivially self-evident.
Of course, the simple fact remains that even if you and all the other scientists working in the field did have the vast quantities of physical data rendering 'transitional forms' trivially evident, including enough formalin jars of specimens to resurface an entire continental land mass, along with 10 million years' worth of continuous video footage of those specimens giving rise to each other in life, and complete genome data resident on exabytes' worth of hard drives on servers, creationists would still deny that evolution happened, and would still insist that fucking magic was needed.
susu.exp wrote:Calilasseia wrote:Even if we make the massively conservative assumption that all the genes in an organism's genome obey simple Mendelian laws (which underestimates the number of possible genomic combinations by a large factor, given the data that exists with respect to genes such as the Rhesus D factor gene in humans), such an assumption leads to the conclusion that, for an organism with 25,000 such genes, the number of possible combinations is 225,000, a gigantic number of possible variations that can exist even in the absence of mutations. Consequently, the scope for variation to be disseminated to future generations is enormous, and with each new generation, the population will change.
There are some problems with this. Mendelian does not imply that there are two alleles for each locus, in sensu stricto mendelian laws imply complete diploidy and no linkage. So you get the product (i=1..2G)ni, where G is the number of genes and ni is the number of alleles of the ith gene. G however is not identical to the number of genes for humans floating around. This number is the number of genes in the sense of molecular biology. It is not identical with the number of genes in the sense of evolutionary biology. A gene in the later sense isn´t neccessarily a DNA sequence - amino acid sequences are another example. To provide an example where this is relevant: Suppose there are 4 different DNA-alleles coding for an amino acid. Two of them code for one AA-sequence differing only by a synonymous substitution. The other two code for another AA-sequence (again differing by a synonymous alteration). It is possible in such case, that all DNA-genes are in the near neutral realm, but there is significant selection on the AA-genes. Evolutionary genes extend even to morphological character states. I´ve got two legs. That is an evolutionary gene. To make that more precise: An evolutionary gene satisfies the following criteria:
a) Heritability - it must be passed on from parents to offspring.
b) Imperfection - Variation must be able to arise
c) Stability - there are mathematical boundaries to the rate at which variation arises compared to the rate it is inherited
d) Discreteness. The number of legs is an integer. Any amino acid in a sequence of amino acids is one of the 400 AA known (and with few exceptions one of the 20 essential ones). And DNA sequences have at any point one of the 4 nucleotides.
d) is often not stressed and that´s one of the reasons I dislike statements to the effect of "it´s all a continuum" or "nature isn´t discrete. Discretness is a central point in evolution - without discreteness you don´t have genes and without genes you don´t have evolution.
Well I was presenting an elementary analysis by my own admission in that post.
However, the problem is that even elementary analyses tend to be beyond the ability of creationists either to understand or to erect. But then what else do you expect when their entire world view consists of "doctrinal assertions matter more than reality"?
susu.exp wrote:Calilasseia wrote:Actually, Ichthyornis is regarded as being a member of a sister clade to modern birds, the Subclass Ichthyornithes, which is taxonomically distinct from the Neoaves to which modern birds belong, but sharing a common ancestor therewith via the Carinatae. Therefore your above assertion that this was "100% bird" is not supported by the taxonomic evidence. It's part of a lineage with no modern descendants. Tell me, did you ever bother to learn anything about basic cladistics?
I think in this case you´re not on solid ground with the cladistics either. Ichthyornites, as a sister clade of the Neornithes is of course a subclade of Aves:
(Velociraptor(Archaeopteryx(Ichthyornithes(Neornithes))))
Birds in bold, Modern birds in italics as well.
Ah, I was under the impression that Ichthyornithes were a sister clade, not a containing clade. I stand corrected.
Once again, you know more about this than I do, and so I won't argue. I was, however, aware of the more elementary fact that reptiles sans Aves were not monophyletic. And a quick trip to the Tree of Life website informs me that reptiles themselves form two distinct clades, the Archosauromorpha and the Lepidosauromorpha, the former being the clade containing birds, the latter the clade containing mammals, and that consequently, 'reptile' in the Linnaean sense is probably polyphyletic even without the additional complications you allude to above. But then that's what science does: modify its understanding as more real world data becomes available, as opposed to the creationist process of pretending that mythological assertions constitute "axioms" about the world, and then trying to force-fit the square peg of reality into the irregular hole of doctrine.
