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Author | Topic: questions evolutionists can't or won't answer | |||||||||||||
mark24 Member (Idle past 5216 days) Posts: 3857 From: UK Joined: |
quote: Percy beat me to it, but this comment wasn't addressed. Why do you need to see speciation through natural selection, particularly? As opposed to genetic drift, peak shift, ecological selection, sexual selection, polyploidy, etc.? Just curious as to why you're placing such emphasis on speciation by ns. Mark ------------------Occam's razor is not for shaving with.
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mark24 Member (Idle past 5216 days) Posts: 3857 From: UK Joined: |
Temper!
------------------Occam's razor is not for shaving with.
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mark24 Member (Idle past 5216 days) Posts: 3857 From: UK Joined: |
quote: Hi JP, There’s a few misconceptions here that I’d like to tackle, if I may. Phylogenetic inference is a method which we infer relationships of genetic sequences. It is important to make this distinct from the inferred species tree from such analysis’. To reliably be able to infer a species tree, we may need several gene/data trees, maybe morphological trees as well, in order to get a reliable enough consensus. Imagine a species tree to be a glass pipe stretching back into the past. Within this pipe are cotton threads representing gene lineages. Now, imagine a gene for normal colour sight that gets a mutation & becomes the colourblind allele. At some point in the past, if you trace the two threads (alleles) back to the the mutation point, they will join. This is called a coalescent event (it’s arse about face, if you ask me, but in the interests of using the same definitions as everyone else.). As such, gene lineages aren’t expected to completely match species lineages. It gets more complicated if the coalescent event occurred before speciation, because you have one pipe getting itself a Y connector (speciation event), with both alleles splitting & heading up different pipes (separate species), for a total of four threads. BUT, it matters not one iota whether that gene allowed excellent colour vision or not (I’m assuming, purely for the sake of argument that colour blindness is caused by a mutant allele, I could easily use any gene), because you are tracing back two (or more) homologous alleles (from different species) to the coalescent event, which is what [/I]infers the relationship[/I]. The allele frequencies that cause the inheritance patterns is an utterly separate issue. As I have said above, gene lineages need not match exactly (in real life) the species lineage, but nails down most of the details. Unresolved parts of the first tree may be resolved by a second & third molecular phylogeny using different genes/data sets. In the end, we can reliably infer a species tree using multiple congruent phylogenies derived from many different & diverse data sets. Of course, the above requires sequences that are both different enough to be informative, & homologous. This is why a single polymorphism isn’t adequate to infer very much. As a result, not being able to infer relationships from a sickle cell allele, or trisomy 21, isn’t exactly falsifying molecular phylogenetic inference. We are attempting to infer species trees from sequence data (cotton threads) that that has survived in a direct unbroken lineage all the way up those pipes, being split into two, & threaded up two pipes (Y connectors) potentially many times. There are threads that don’t make it, & are lost, we can only infer from the extant threads that poke out the top (present day). If common descent is true, then phylogenetic analysis should consistently show (& there are reasons why it doesn’t) that homologous sequences are related, & subsequent studies should be broadly congruent. They are. Apologies for the analogy, it just seemed easier.
quote: You are confusing inheritance patterns with phylogeny. Assuming you had sequence data of homologous colour-blindness genes between humans & apes, you could infer a phylogeny, provided that there were enough informative differences between extant sequences, or you had a large variable sample, & then similarities would mean recent divergence.
quote: Irrelevant. No passing on of DNA, no phylogeny from which to infer anyway!
quote: Irrelevant. This has nowt to do with inferring phylogenies, except the first sentence that describes a coalescent event.
quote: Regarding sickle cell, you may be right. But since it’s a single polymorphism that proves to have a net beneficial effect to the owners in malaria infested Africa, it’s entirely possible that the identical alleles arose more than once, incidences of trisomy 21 certainly do. In any case, a single polymorphism across the entire potential range of samples isn’t enough to infer a phylogeny with, except a close relationship with the original heamaglobin. But that’s not what were talking about, is it? Were talking about homologous sequences between species, not people, that have A LOT in common. Suggesting that these alleles arose spontaneously alike, & were then fixed, neutral loci as well, is an entirely different prospect to a single polymorphism. Not only did they arise spontaneously alike, phylogenetic inference shows that they are congruent with other genetic phylogenies. By chance? The odds are colossally against such an event. An 11 taxa phylogeny has 34,000,000 possible trees. I’ll give you the benefit of the doubt & assume that two phylogenies for the same 11 taxa was only 50% congruent. That’s 17,000,000 * 17,000,000 = 289,000,000,000,000 : 1 odds that such an event occurred by chance. Because of this, & the fact it occurs over & over, most people reasonably accept that phylogenetic analysis is good evidence of common descent.
quote: Nope. If a mutation doesn’t get passed on, we can’t infer from it. If a mutation isn’t fixed, & worse, is lost, the same applies.
quote: This has nothing to do with molecular phylogeny either. With respect, JP, you have left the subject of molecular phylogenies behind, more than once. Talking about something other than molecular phylogeny doesn’t falsify molecular phylogeny, now, does it? Nor does confusing inheritance patterns with inferring phylogenies. Mark ------------------Occam's razor is not for shaving with.
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mark24 Member (Idle past 5216 days) Posts: 3857 From: UK Joined: |
[QUOTE]Originally posted by John Paul:
[B][quote]F. Hind limbs. John Paul:Again, that would only be assuming they were once limbs. Do you have any evidence to support that? [/B][/QUOTE] I can't speak for baleen whales, but Sperm whales have vestigial hind limbs. A pelvic girdle is present in all sperm whales, but in a few individuals only, abutting the pelvis, bones are in evidence. The expression appears as 1 to 10 bones, depending on individual. Why on earth are they there? They have no function, else they'd be in ALL members of the species. It appears that the expression of these bones is an atavism, an expression of alles that have a low frequency, & are being removed from the genome, or have at least have had their frequencies reduced purely by genetic drift. Mark ------------------Occam's razor is not for shaving with. [This message has been edited by mark24, 08-15-2002]
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