TCups said:
But isn't that a "beak of the finch" argument? MRSA is still staphylococcus aureus, and drug-resistant TB is still a mycobacterium, not a protozoan. Environmental adaptation occurs without a doubt and occurs very rapidly. This is a proven observation that I don't dispute.
No, the argument you are figuring to setup here "micro vs macro" evolution is one perpetuated by the billion dollar creationist industry. Macroevolution
is microevolution. They are one in the same process. The only difference is some subjective definition of time elapsed since a coalescent point.
TCups said:
Speciation if I understand that term correctly -- the "evolution" of one distinct species into an entirely new species -- to the best of my knowledge (obviously limited) has not been observed in any laboratory experiment or ever irrefutably proven by any complete fossil record,
Modern "species" don't evolve into other modern "species"--A species is only so by way of its lineage. No matter how many children you have and how different they look from you they will never be the children of a distant cousin. Ergo, bacteria don't evolve into "cats" or "dogs" or "fronkies". And anything that bacteria "evolve" into will always belong to the "kind" bacteria, because bacteria is a
rank of organisms which
share a common ancestor and will always share said ancestor.
As far as "speciation" goes, the first step to understanding that is understanding that species are not real, tangible things. They are (like the definition of life) a ranking bestowed by people upon populations.
Populations who split can no longer share genes between them. That is to say they are
reproductively isolated (searchable term) and therefore any changes modulated to their gene pool will accumulate separate changes. When these changes are enough that the populations no longer interbreed even when brought back together-we say we have "speciation". Because, without interbreeding their lineages will continue to diverge in a manner reflective of the selective pressures on each gene pool.
There are many barriers to gene flow. They can be pre-zygotic, such as a penis not fitting to a vagina, sperm receptors of the zona pellucida differing, behavioral nuances (time of day matting occurs, season matting occurs, mating displays etc) and many others. There can also be post-zygotic barriers, ie; fertilization occurs but the zygote is non-viable, the offspring is non-viable, the offspring is sterile etc.
As for reproductive isolation being observed in the lab? Maybe you are not familiar with
http://en.wikipedia.org/wiki/Speciation#Artificial_speciation"?
TCups said:
fossil records being temporally limited to a few thousand years.
I'm not sure what you are stating here, do you mean to say that the fossil record is only a few thousand years old?
TCups said:
And the theory of evolution, I believe (please correct me if wrong) would seem to imply that "speciation" must be a long-term consequence of natural selection, ending in the present biological diversity, but occurring over much longer time intervals than can perhaps be observed experimentally.
No, the modern synthesis simply says that when reproductive isolation is achieved, because of selection, the two gene pools will diverge. Over how long, and under what kind of selection will determine how "different looking" the extant lineages will become.
TCups said:
As for entropy (and ice cubes) . . .
My poorly stated argument - apologies. May I reframe the argument? How did the first simple biological life form "evolve" from something else?
Biological evolution is not synonymous with abiogenesis. Surely, as a physician, you are aware that scientific theories explain specific scientific phenomena? You can no more use relativity to explain fluid flow through a tube, than you could the modern synthesis to explain why the continents move about the surface of the Earth (or the origin of life for that matter). We are talking, apples and oranges--mechanistically speaking.
Nevertheless, the origin of life is still an interesting question that we are still looking for the answer too. There is some things we do know about that origin. For starters, we know that a molecule had to have the ability replicate. Probably through a spontaneous process and later auto-catalysis. We know that the first replicator would have had to have a "book keeping" ability, ie ability to transmit information across generations and that resources spurred competition and differential survival/reproduction of those replicators.
Its for this reason that RNA seems to get the lead role in the search for the origin of life and probably the best supported hypothesis (at the moment) being the http://en.wikipedia.org/wiki/RNA_world_hypothesis" .
We know RNA can be auto-catalytic (recall from your biochemistry classes what rRNA is and does). We know that RNA polymerizes fairly easily (there was an interesting paper on here some time ago about how RNA polymerization would have been very favorable under prebiotic conditions reducing the entropy of the earth-sun system-http://arxiv.org/PS_cache/arxiv/pdf/0907/0907.0042v3.pdf" ) and we also know that RNA can act as a carrier of hereditary information across generations (remember those guys we call RNA viruses?)
TCups said:
How might DNA (or even RNA) spontaneously assemble itself from simple amino acids and having done so, evolve to become self-replicating and then, ever more complex?
Well granting that you meant "nucleic acids" here (I sincerely hope a physician practicing medicine in the 21st century is aware of what RNA and DNA is made of), see above.
TCups said:
Nothing in my education or experience gives me a clue to a natural, physical process that would tend to have this result, least of all, random chance.
You education should clue you into the word "
selection" in the phrase "natural selection".
The biological fact of evolution is that allele frequencies for a gene pool change from generation to generation. The is simply the fact. In science, we like to explain facts-because facts by themselves are worthless and tell us nothing about our world or how it works.
The modern synthesis is a scientific theory which explains the biological fact of evolution-Namely that adaptive evolution is driven by natural
selection. Implied in this are one of the things Darwin got right about evolution-Namely his "four postulates" of natural selection; That there is variation in a population, that some of that variation is passed on to offspring, that resources in any environment are limited, and that some of those variants will be better or worse at surviving and reproducing than others. Hence, we have
differential survival and reproduction--A non-random process.
What Darwin (and Wallace) really discovered was a syllogism of another process that humans had been doing for thousands of years--Artificial selection. Meaning, that humans
choose which individuals in a population will pass on their traits to the next generations. Dog breeders, horse breeders, plant breeders, for generations have been using
selection to alter the frequency of alleles expressed in a population.
By the same token, non-humans, have also been breeding populations for specific traits. Bees
choose flowers for their appeal, herder ants breed aphids and Damselfish breed algae.
Darwin's genius was to realize that there doesn't have to be chooser to determine who gets to pass on traits. The simple observation that animals who die before reproductive age or who reproduce poorly, like a dog you don't breed because it lacks a trait that appeases your sense aesthetics, will "sit out" of the future gene pool. In other words, selection without a selector.
TCups said:
Here's another question on my mind:
mitochondrial DNA. I know, in general, that it is passed down through the female lineage and links much of our human species to a single female African ancestor. But not only humans have
mitochondria and
mitochondrial DNA. Has there ever been any inter-species (vs. intra-species) links of the
mitochondrial DNA of one species to another species?
Yes, one only needs to do a literature search on
mitochondrial DNA clocks.
