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| quote: | Originally posted by NeoPhono
There are several modern day "problems" with the current theory of evolution. I'm not saying evolution doesn't take place, but the way we think it does is coming into contention. I took an entire course on this a few years ago, "Modern Topics in Biology," but my retention has not been the best. |
IOW, it's a dynamic theory?
But in no way has the central argument of the theory changed - mutation and natural selection arises changes in a population over time.
| quote: | | First, it has been shown that evolution is not a gradual process, as once thought, where generations lead to further generations due to the reproductive success of ancestors and these reproductive "improvements" are passed on (natural selection). Rather, there are speciation events that are random and have nothing to do with reproductive success. These primarily include natural disasters such as large volcano eruptions or meteor impacts. |
Actually both can occur. Take the famous peppered moth for example. No reproductive isolation was necessary at all, just a mutation within that population. But in regards to speciation, of course this can occur as a result of reproductive isolation. If that's not common evolutionary thought, I don't know what is. But is it exclusive to geographical barriers? Absolutely not. Speciation occurs when a pop'n of a given species has a reproductive barrier or some sort that prevents hybridization with the other members of the species, whether it be a gradual thing such as an increase in hybrid incompatibility between populations over many generations (peppered moth), a sudden geographical separation and differential environmental pressures cause a barrier to gene flow so that after only a few generations even if the populations were reunited they are incompatible (geographical isolation), or it can also be sympatric based on changing host specificity, or some behavioral change necessitated by occupation of a novel or marginal niche, etc etc etc.
Many definitions of isolation.
| quote: | | One notable example is the Cambrian explosion (although I believe there are three other "explosion" examples), where after a meteor impact you had a speciation event that was caused by remaining inhabitants spreading to fill open niche, not reproductive success. |
There's a great deal of unknown about the CE to make such a conclusion just yet. A variety of other environmental factors also likely played a role:
(1) a distinct fluctuation of carbon isotopes around
the Proterozoic-Cambrian,
(2) a dramatic increase of the d34S curve,
(3) an increase of the global sea-level,
(4) a distinct rise of the phosphorite production,
and
(5) a slow increase of oxygen in the atmosphere from
late Proterozoic to early Phanerozoic times.
http://www.uni-wuerzburg.de/palaeon...casu8.htm#explo
As to how these events occurred, via a meteorite or some other cosmic phenomenon is still a bit of a guess, but it's still a bit of a mystery. But in regards to evolution, that of course occurs when allele frequencies change within a gene pool. Speciation separates gene pools permanently (which can change allele frequencies), reproductive isolation interrupts gene flow, which allows speciation to occur. Again, this is common knowledge in evolution.
| quote: | | Second is the idea of mutation driving evolution. It has been mathematically shown that there are not enough beneficial mutations per time to give rise to evolution the way we have seen it. There are many times more harmful mutations then beneifical and even the beneficial ones have a very small chance of being passed on and eventually assimilated into a population. You can infer how many mutations it would have taken to get from the beginnings of life to where we are today, and you can see the mutation alone falls hopelessly short. |
But you're leaving one critical factor out here in referring to evolution: natural selection. While true the mutation rate (harmful/neutral/beneficial) would certainly NOT favor or explain in any manner the gradual changes we see today, the second critical factor, natural selection does. It weeds out those harmful mutations, while positively selecting the beneficial ones. And the neutrals more or less tend to just come along for the ride.
And something else needs to be considered about mathmatical models of past mutation events - we really don't have very good figures regarding "beneficial" mutations at all, let alone have enough worthwhile info. regarding past mutation rates and pop'n sizes. So any calculations on such past events are really more or less than inferred guesses from what we know of mutation rates today, which you seem to agree to as well. But let's take a look at Wright's calculations:
http://www.talkorigins.org/faqs/faq...y.html#mutation
Here's the equation:
| quote: | | First a mutation occurs in an individual, creating a new allele. This allele subsequently increases in frequency to fixation in the population. The rate of evolution is k = 2Nvu (in diploids) where k is nucleotide substitutions, N is the effective population size, v is the rate of mutation and u is the proportion of mutants that eventually fix in the population. |
Now let's look at the beneficial mutations:
| quote: | | Most new mutants are lost, even beneficial ones. Wright calculated that the probability of fixation of a beneficial allele is 2s. (This assumes a large population size, a small fitness benefit, and that heterozygotes have an intermediate fitness. A benefit of 2s yields an overall rate of evolution: k=4Nvs where v is the mutation rate to beneficial alleles) An allele that conferred a one percent increase in fitness only has a two percent chance of fixing. The probability of fixation of beneficial type of mutant is boosted by recurrent mutation. The beneficial mutant may be lost several times, but eventually it will arise and stick in a population. (Recall that even deleterious mutants recur in a population.) |
So it comes down to a 2% chance of fixation. Seems pretty small at first. Well let's break it down to a hypothetical example. I can't take credit for this example, but I saved it from a blog a while back: Let's say I'm Joe Q. Organism. In my genome there's about 20,000 active gene sites, but since I have 2 copies of each chromosome, I actually have 40,000 mutatable genes. Adding up my conspecifics and me comes to one million organisms in my generation. That's 40,000,000,000 mutatable gene copies total in the gene pool.
Now according to Wright, every one of those genes has about a one in 10,000 to one in 100,000 chance of mutating. Let's go halvsies so we'll estimate that each gene has a one in 45,000 (that's half of the difference between 10,000 and 100,000) chance of mutating.
So far we have, on average, 888,888 mutations in the entire gene pool. Wright says that one in 1000 of those is benefical, so we have almost 900 beneficial mutations. Two percent of those will fix, so 18 beneficial mutations from that population will become permanent.
18 mutations out of one generation of one million conspecifics. Sure, that's not a lot. But in three years (for example), when this generation has hit sexual maturity, that million will have dwindled to maybe a tenth of that. Then they'll have another million children, or ten per organism. 180 of those individuals have the beneficial mutations from the last batch, and there's another 18 mutations this time.
Over 500 million years, it adds up. For our hypothetical population of organisms that's 3 billion benefical mutations. And you're telling me you don't think 3 billion benefical, permanent mutations are going to constitute significant evolutionary change to a population of organisms? I hardly think so.
And finally, the mutation rates measured within organisms is in line with the DNA differences seen between organisms. IOW, the rate at which mutations occur in an organism matches up with the span of time since common ancestory. Here's just one abstract that evidenced the mutation rate in fruit flies with the changes seen in the fossil record and with extant fruit fly species. The final conlusion is that the mutation rate is sufficient to result in the DNA differences we see between species:
| quote: | Mol Biol Evol. 2004 Jan;21(1):36-44. Epub 2003 Aug 29.
Temporal patterns of fruit fly (Drosophila) evolution revealed by mutation clocks.
Tamura K, Subramanian S, Kumar S.
Center for Evolutionary Functional Genomics, Arizona Biodesign Institute, and School of Life Sciences, Arizona State University, USA.
Drosophila melanogaster has been a canonical model organism to study genetics, development, behavior, physiology, evolution, and population genetics for nearly a century. Despite this emphasis and the completion of its nuclear genome sequence, the timing of major speciation events leading to the origin of this fruit fly remain elusive because of the paucity of extensive fossil records and biogeographic data. Use of molecular clocks as an alternative has been fraught with non-clock-like accumulation of nucleotide and amino-acid substitutions. Here we present a novel methodology in which genomic mutation distances are used to overcome these limitations and to make use of all available gene sequence data for constructing a fruit fly molecular time scale. Our analysis of 2977 pairwise sequence comparisons from 176 nuclear genes reveals a long-term fruit fly mutation clock ticking at a rate of 11.1 mutations per kilobase pair per Myr. Genomic mutation clock-based timings of the landmark speciation events leading to the evolution of D. melanogaster show that it shared most recent common ancestry 5.4 MYA with D. simulans, 12.6 MYA with D. erecta+D. orena, 12.8 MYA with D. yakuba+D. teisseri, 35.6 MYA with the takahashii subgroup, 41.3 MYA with the montium subgroup, 44.2 MYA with the ananassae subgroup, 54.9 MYA with the obscura group, 62.2 MYA with the willistoni group, and 62.9 MYA with the subgenus Drosophila. These and other estimates are compatible with those known from limited biogeographic and fossil records. The inferred temporal pattern of fruit fly evolution shows correspondence with the cooling patterns of paleoclimate changes and habitat fragmentation in the Cenozoic.
(emphasis mine).
www.pubmed.com |
| quote: | | Basically modern evolution theory is transforming from one driven by mutation and natural selection to one driven by random speciation events. It is not a gradual mutation over time that leads to higher fitness, but random events that lead to "species selection" in which chance plays the most important role. |
Well like I mentioned earlier, gradualism and reproductive isolation are not mutally exclusive in the overall process itself.
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Whence September dusk grows crisper still,
with leaves all crimson conquered,
I yearn to shout,
and dance about,
and stick pickles in my honker...
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. Opus has supplanted your rational authorative position but even he has been slacking as of late when it comes to the daily grunge or dismissing utter bullshit. What have you been up to? 
