Planet Humping (Panspermia looking like a good theory these days)

[dalovindj]

Panspermia: (http://www.panspermia.org/)

Here's (http://www.space.com/scienceastronomy/solarsystem/comet_life_010405.html) a great one. Here's (http://www.spacedaily.com/news/life-01zb.html) another good one.

I wonder how long it will take to find some of these space seeds, if they exist. I hope soon!!!

DaLovin' Dj

[Duck Duck Goose]

DJ, in Great Debates you're supposed to post an opinion, tell us what you think, so we can have a debate. Otherwise, this is just MPSIMS material, babe. ;)

We can't really debate "how long do you think before we find some space seeds?"

But I do like their motto: "Life comes from space because life comes from life."

Right.

[tracer]

Duck Duck Goose wrote:

But I do like their motto: "Life comes from space because life comes from life."
Uh ... huh.

Hmmm. Where do the people who thought up this motto think that the first life came from, anyway? The Big Bang?!

[Duck Duck Goose]

Space is life, because it's full of spores, which are alive. See?

And as to where the spores came from, well, obviously, they came from the same place that spores always come from--from fruiting bodies of some kind. So obviously there was no Big Bang, but instead there were Primeval Extraterrestrial Fungi somewhere on an alien planet, which produced spores.

It's not that difficult, Tracer. Sheesh.

[ultrafilter]

Originally posted by Duck Duck Goose
....there was no Big Bang, but instead there were Primeval Extraterrestrial Fungi somewhere on an alien planet, which produced spores.

Cthulhu fhtagn! Iaaeeh! Iaaeeh!

;)

[tracer]

Duck Duck Goose wrote (and I'm quoting completely out of context here):

So obviously there was no Big Bang,
Aha! I knew it! Panspermia advocates are all secretly Creationists!

I shoulda known when I saw Duane Gish, Philip Johnson, Ken Hovind, and Ken Ham on the Board of Directors....

[edwino]

All you've done is doubled (or at least procrastinated) your problem.

Where did the original life come from? Panspermia or seeding or whatever is an interesting idea, but doesn't really explain anything or answer any questions. Your website freely admits that. All panspermia does is add another link in the chain in the question "Where did life come from?" And that site has wacky points about the Big Bang theory and wormholes and other stuff.

What I find more interesting is the theory that oil is not necessarily a by-product of surface life, but indeed is a natural feature in planets, and can be created and maintained by a deep, hot biosphere. This means after suns burn themselves out, planets or planetismals that remain warm can transport life from system to system. This theory has been forwarded by Thomas Gold, the guy who postulated and then helped discover quasars (argument from authority, I know). Described as a "world-class contrarian", he may be just your type, dalovindj.

Here is a nice Wired interview with him.

http://www.wired.com/wired/archive/8.07/gold.html

[elucidator]

One of my all time favorites, good ol panspermia

While it doesn't answer the question as to the ultimate origin of life, it does have some utterly fascinating effects. First and foremost, at least to my mind, it opens up more time. I have always been troubled by that.

Suppose you take all the cogs, wheels, gears, transistors etc. in the world, and rolled them down a ten-thousand mile slope, then scooped them up and rolled them again, as many times as one wished. Sooner or later, those pieces will accidentally assemble into a self replicating robot, which, is a rather crude but effective metaphor for DNA. But your going to need lots of time, the Saganesque "billions and billions and billions". But our recent studies seem to indicate that Earth became infested with DNA at a very early point in time, perhaps only a few millions of years after it cooled enough to be a solid. This contradiction is neatly solved by panspermia. Also, its really cool.

More interestingly, it implies that life, rather than being delicate and unlikely, is sturdy and damn near inevitable, it will exist so long as conditions do not absolutely prohibit it. When you look up into the night sky, you are seeing billions of stars, and gigazillions of living things. More importantly, DNA based living things, like ourselves!

We could eat them! Chicken-fried bandersnatch, anyone? Tribble sushi?

To paraphrase St. Pogo, "We are either the most intelligent beings in the Universe, or we aren't. Either way, its a mighty sobering thought"

[edwino]

Originally posted by elucidator

Suppose you take all the cogs, wheels, gears, transistors etc. in the world, and rolled them down a ten-thousand mile slope, then scooped them up and rolled them again, as many times as one wished. Sooner or later, those pieces will accidentally assemble into a self replicating robot, which, is a rather crude but effective metaphor for DNA. But your going to need lots of time, the Saganesque "billions and billions and billions". But our recent studies seem to indicate that Earth became infested with DNA at a very early point in time, perhaps only a few millions of years after it cooled enough to be a solid. This contradiction is neatly solved by panspermia. Also, its really cool.


Gonna nitpick here. By all estimations, we don't need more time. There has been between 2 and 3 billion years since evolution began on this planet. 545 million since the Cambrian explosion. We have diverged from mice in 60 million.

Your robot example is also relatively meaningless. At all points in evolution, there has been selection. Your example has no selection. At all times in evolution, the most evolved organisms passed their genes on most frequently. So instead of a truly random process resulting in a robot, you have a process at which each step is regulated, but there is no clear endpoint.

To borrow an analogy from Richard Dawkins, your example is like monkeys randomly banging on typewriters to create Shakespeare. Everything is discarded, except that which is Shakespeare. (It can't be off by even one letter.) Evolution is like starting with a random string of letters, keeping only the ones which resemble Shakespeare, and then resubmitting the blanks between those letters for more random monkey trials:
TQWIO UJENASLKD HA
TOIUM AKANWLAJS SK
TOTND HRYN JMTT NT
TOLDE TRBNJDVTY UK
...selection...
TO BE OR NOT TO BE
This is obviously the shorter route to take when generating Shakespeare. Of course evolution has no definable end point, but it is still a useful analogy to show that evolution can move quickly.

[elucidator]

Entirely valid. However, the processes of selection and the resulting acceleration, can only come into play after DNA based life exists. The "self-replicating robot" I'm talking about is the DNA molecule itself, which apparently I did not make clear. There is no real evidence to bring to bear on this issue, but my guess is that there isn't enough time between the point at which the Earth became less than totally hostile to life and the first clear evidence of life for DNA to happen if we are positing strictly random chemical interaction.

If we have, however, the life-span of the Universe rather than the (comparatively short) Earth, it becomes at least that much more feasible.

[edwino]

IMHO, not really. All you really need for selection with replication is an RNA molecule. DNA is a relatively unnecessary second layer of complexity. Even something like classical RNA is not really necessary, one can evolve to that point. All that is needed is a nucleic acid like substance that can replicate itself. While this sounds complex, we have made RNA which comes close -- it can polymerize RNA and partially replicate itself. Give us a few years and we can, in 20 years of PCR, replicate what nature had around a billion to do.

[Chickenhead]

...and it seems, I would say, logically questionable.


Southern cuisine comes from Zeus because southern cuisine comes from southern cuisine.

Geena Davis impersonators come from Belgium because Geena Davis impersonators come from Geena Davis impersonators.

Gasoline comes from smegma beca

Well, it does seem questionable. Although IIRC most Geena Davis impersonators are Belgian.

[Badtz Maru]

Originally posted by elucidator
One of my all time favorites, good ol panspermia

W More importantly, DNA based living things, like ourselves!

We could eat them! Chicken-fried bandersnatch, anyone?

Bandersnatch are not based on DNA. They are massive single-celled organisms with chromosomes so big they can be seen with the naked eye.

[ACoverOfNoise]

edwino


Gonna nitpick here. By all estimations, we don't need more time.


Well, as long as we're nitpicking... Unless you are privy to some knowledge that seems to have escaped the rest of the scientific world... we don't KNOW if we need more time or not. No one has successfully calculated all of the probabilities to know whether or not there was enough time for abiogenesis. No one even knows what all of the degrees of freedom are in this probability equation. Also, the point that elucidator was making was not about the 2-3 billion years to evolve from the first organism, but the 300-500 million years for the first living, self-replicating organism to appear.

But then, you did use the word "estimation" so I guess that let's you off the hook. Great word. It carries with it an implication of actual information without requiring all that pesky data... ;-)

[edwino]

What I was trying to say was that the theories of evolution and abiogenesis are based on data. These data include things like probable composition of Earth's early atmosphere based on planetary modeling , how much time there was for the stuff to go on based on radioisotope dating, biological data on the reactivity of particular types of molecules, for instance the ability of RNA to catalyze an RNA polymerization reaction. The theory has to fit the data, so any theory of abiogenesis without panspermia has to fit the observed time scale. Since in my readings, time scale has never been an issue, I assume that scientists theorizing about abiogenesis are not too concerned with it. Certainly the ones theorizing about evolution are not terrifically nervous about cramming all of observed life into the 3 billion years that they probably have to work with.

[ACoverOfNoise]

What I was trying to say was that the theories of evolution and abiogenesis are based on data.


Well continuing to nitpick:

(1) The formulation of the theory of evolution (AKA Darwinian evolution) was not based on data. It was based on some basic observations and some deductive reasoning. Most of the supporting data came after the theory (which is, incidentally the way it usually works in science).

(2) I do not share your assumptions about the data.

First we may need to define what you mean by "the theory of evolution". If your definition is that evolution is a change in the genetic characteristics of a population over time, there's plenty of data to support that.

If your definition of evolution is that natural selection is largely responsible for the transition from the first theoretical single celled organisms into all of the known lifeforms that ever have and ever will inhabit this planet... well, there's significantly less data to back that up. In fact, some of the data seems to be contradictory to that theory.

Because I know many of the scientific processes and techniques employed in data gathering in this field, and recognize that most of the analysis is done in an environment that assumes that the central premise is true, I don't "assume" that the supporting "data" is not worthy of question.


The theory of abiogenesis has even less to go on. Many of the experiments that produce "data" to support the theory (such as Miller-Urey) are based on other theories, about the nature of the early Earth, for instance. These theories, also have little or no supporting data and, in fact, some rely on still other unsupported theories.



Since in my readings, time scale has never been an issue, I assume that scientists theorizing about abiogenesis are not too concerned with it.


In fact, there are many scientists and mathematicians that have serious concerns about the time scale. Attempts to calculate the basic probabilities of even the most basic steps have come up with improbable numbers. Actually, some of these numbers exceed the age of known universe, but that doesn't bode well for panspermia, either.

Personally, I'm betting on abiogenesis, but I think there must necessisarily be catalysts, chemical principles, and other processes that we have yet to discover (and perhaps never will) which led to that "blessed" event. However, until I know with greater certainty, I leave room in my philosophy for other theories, including, but not limited to panspermia.

[Lemur866]

OK, I'll bite ACoverOfNoise. WHAT data contradicts the idea that all life on earth comes from a common ancestor? Are you talking about extremophile bacteria? But as far as I know, every organism on planet earth uses the same amino acid codon sequences. I can see no objective reason to link any codon to any amino acid, so the only explanation is that all life has a common ancestor.

You can't just toss out casually that all our evolutionary theories are wrong without doing some backup work. Of course we don't have any good theories of biogenesis. This disproves evolution....how?

[edwino]

I will bite, too, Cover, with two preconditions:
1) I will not hijack this thread any further after this post. If you want to debate faulty science behind evolution, start a new thread to do it, and I will gladly be there.
2) Since I am a molecular geneticist, the organic synthesis of proteins, lipids, and ribonucleic acid in abiogenesis interests me, but I have little knowledge in the region. I am interested in the world after selection with descent started, and that is where I will begin. I will say that our body seems to synthesize ribonucleic acids and proteins every day from 2 and 3 carbon substrates. It seems likely to me that in the correct environment, given a few hundred million years, similar things could happen.
Originally posted by ACoverOfNoise

Well continuing to nitpick:

(1) The formulation of the theory of evolution (AKA Darwinian evolution) was not based on data. It was based on some basic observations and some deductive reasoning. Most of the supporting data came after the theory (which is, incidentally the way it usually works in science).

I don't know how you define data, but in my lingo, observations are data. I agree with your next sentence -- deductive reasoning and observations behind the hypotheses, continued observation of new data to form a theory.

(2) I do not share your assumptions about the data.

First we may need to define what you mean by "the theory of evolution". If your definition is that evolution is a change in the genetic characteristics of a population over time, there's plenty of data to support that.

If your definition of evolution is that natural selection is largely responsible for the transition from the first theoretical single celled organisms into all of the known lifeforms that ever have and ever will inhabit this planet... well, there's significantly less data to back that up. In fact, some of the data seems to be contradictory to that theory.

I will disagree with you about their being "less data to back that up." There are reams of comparitive genomic analyses, protein homology studies, mitochondrial and Y chromosome DNA analysis, and observations of speciation in fruit flies. The molecular analyses by-and-large agree with the general taxonomic pattern established by fossil morphology. This all points to a continuum of descent with modification. This all points to common ancestry, for instance the striking 98% homology between histone H4 in E. coli and humans. One data point in a huge field, though. I'll invoke Ben here and say that there is little reason for the pattern of protein homology unless you accept a descent with modification origin of species.

Because I know many of the scientific processes and techniques employed in data gathering in this field, and recognize that most of the analysis is done in an environment that assumes that the central premise is true, I don't "assume" that the supporting "data" is not worthy of question.

As do I. I work on a highly conserved network of genes in the fruit fly Drosophila melanogaster. Some of the genes are so highly conserved that mouse and chicken homologs can rescue Drosophila mutants. I read my papers with a critical eye, and I can recognize when pieces of the puzzle don't fit together. That seems not to be the case with evolution, as almost all observations from numerous areas of science -- geography, paleontology, anatomy, genetics, ecology, and biochemistry to name a few -- all support evolution.

The theory of abiogenesis has even less to go on. Many of the experiments that produce "data" to support the theory (such as Miller-Urey) are based on other theories, about the nature of the early Earth, for instance. These theories, also have little or no supporting data and, in fact, some rely on still other unsupported theories.

I do find the evidence of an RNA world compelling. Self-polymerizing and partially self-replicating RNA has been made in the lab with techniques less than a decade old. The intron/exon structure of genes somewhat supports an RNA origin of life. More than that, RNA forms the key catalytic components of many of the key reactions in the cell -- namely splicing and protein synthesis, as well as parts of DNA replication (telomere extension). While I cannot safely conclude that this is how life began, I can say that the data are compelling, the story is interesting, and the experiments are for the most part sound.

In fact, there are many scientists and mathematicians that have serious concerns about the time scale. Attempts to calculate the basic probabilities of even the most basic steps have come up with improbable numbers. Actually, some of these numbers exceed the age of known universe, but that doesn't bode well for panspermia, either.

I have seen no such calculations, and in my experience, trying to make the calculations are nearly pointless. We don't know the environmental changes occuring on the early earth, we don't know the migration patterns, we don't know which species survived and which didn't. We can estimate general trends perhaps, but evolution is based on improbable events occuring over large time scales. To estimate the amount of time needed to within 2 orders of magnitude is a task which I would think next to impossible.

Natural selection can be a powerful impetus, leading to rapid species change. Also, Gould may be right about punctuated equilibrium -- we have lots of evidence for events that lead to quick genomic instability and fast change in populations. This only serves to speed things up.

Personally, I'm betting on abiogenesis, but I think there must necessisarily be catalysts, chemical principles, and other processes that we have yet to discover (and perhaps never will) which led to that "blessed" event. However, until I know with greater certainty, I leave room in my philosophy for other theories, including, but not limited to panspermia.
While I can't rule panspermia out, I find no evidence to support it. Therefore, since abiogenesis and evolution IMHO seem to be working adequately, I will stick with them. As is the nature of science, if I see valid contradictory data, then the theories will change. I do have to say that the probability of finding valid contradictory data about evolution is exceedingly small, as it would have to overwhelm an enormous set of data which support it.

[ACoverOfNoise]

Lemur866


OK, I'll bite ACoverOfNoise. WHAT data contradicts the idea that all life on earth comes from a common ancestor?


I didn't say that, and I wouldn't say that. A thesis that all life does not come from a common ancestor is no more provable than the thesis that all life did come from a common ancestor.

The "data" that I was speaking of "seems" to be "contradictory" to natural selection as the principle mechanism in evolution. I couldn't possibly list all of the seemingly contradictory evidence, but perhaps a few examples will suffice?

(1) The "explosive" growth in the number of new species and animal groups in the Tommotian stage of the Cambrian period. That period of only about 5 million years seems to throw a big monkey wrench in the slow gradualistic process of natural selection.

(2) On the other hand, we have the so called "living fossils", animals that remain virtually un-evolved from their ancestors of 200-300 million years ago. Why do some creatures exhibit this evolutionary stasis if, as natural selection suggests, random naturalistic processes should drive change?

(3) Touchy ground here, but doesn't it seem ironic that all known, observed cases of speciation have resulted from artificial selection (specifically hybridization) rather than natural selection? Doesn't it also seem ironic that after thousands of years of selective breeding of cats, dogs, etc. that no new species has accidentally been created?

Now I'm not saying these things disprove that natural selection could be the sole agent of evolution, only that they tend to weaken the argument.


I can see no objective reason to link any codon to any amino acid, so the only explanation is that all life has a common ancestor..


No. That illustrates the problem. That is not the only explanation - it's merely the only one you can think of. There are certainly others - another explanation might be intelligent design. [No. I'm not making an argument for intelligent design, but it can't be ruled out... scientifically - of course, you are free to rule it out philosophically]. There could be others that we've not "thunk" of yet.


You can't just toss out casually that all our evolutionary theories are wrong without doing some backup work.


Who's tossing them out? I'm merely pointing out that they are not beyond reproach. Good scientists will not simply believe a theory simply because someone else says it's so... where would we be if Einstein, Feynman, Hawking and others didn't question conventional wisdom?


Of course we don't have any good theories of biogenesis. This disproves evolution....how?


You're quite adept at placing words in my mouth... I made no such claim. In fact, I think it's pretty clear that these were separate thoughts.


However, let me say for the record that I believe in the theory of evolution and even in the process of natural selection, to a limit. I'm just careful not to cast my beliefs as fact and/or natural law.


In the immortal words of Sir Karl Popper:


The wrong view of science betrays itself in the craving to be right.

[ACoverOfNoise]

edwino:

I agree with you, we've already started to diverge from the intent of this thread, so I'll try to avoid serious hijack, but still answer a few of your questions, as long as they seem reasonably relevant.

By the way, my only intent in joining this thread was to state that throwing out the theory of panspermia is purely a dogmatic reaction. Panspermia actually does allow more time for biogenesis to occur, it may provide for "happier" environments, and it could be used to explain certain other events, such as the Cambrian explosion.


I don't know how you define data, but in my lingo, observations are data.


I'll quote from "The American Heritage® Dictionary of the English Language, Fourth Edition" because it suits me:


* Factual information, especially information organized for analysis or used to reason or make decisions.

* Values derived from scientific experiments.


Observations, in and of themselves, are not data (according to my definition). Observations can be used to collect and assess data.

If you don't mind, I won't continue to argue the point about evolution in this thread. Let's stick to abiogenesis and panspermia. Therefore, I'll leave your next couple of paragraphs unanswered, but let me reiterate, I'm not arguing against evolution anyway.



I do find the evidence of an RNA world compelling.


As do I. However a compelling argument does not a fact make.


Self-polymerizing and partially self-replicating RNA has been made in the lab with techniques less than a decade old.


Slight tangent here. Check me if I'm wrong, but these RNA sequences were made from other RNA sources (ribozyme engineering), were they not? The missing key seems to be getting that first RNA molecule right.


While I cannot safely conclude that this is how life began, I can say that the data are compelling, the story is interesting, and the experiments are for the most part sound.


Agreed, but does this necessisarily preclude the possibility of panspermia? Again, I prefer abiogenesis over panspermia, but my preference is not based on science.


I have seen no such calculations


Can't imagine that in your field... I've seen many versions, most are lame and assume that we went spontaneously from a pool of amino acids to the first proto-bacteria. Some, however attempt to calculate the intermediate probabilities of amino acids into polymers, then from polymers into self-replicating polymers, and so on. They also try to assess probable generation rates and survival rates. Of course, as you point out there's so many assumptions as to make the whole process nearly pointless. However, it does raise valid questions about whether or not 200-300 million years was long enough for the process (whatever it was) to occur, which in turn makes the question of panspermia a valid one.

[ACoverOfNoise]

Oh yeah. Almost forgot the most important point.

While it is a mistake for abiogenesis opponents to think they can calculate the probability of abiogenesis without knowing the complexity of the process and arrive at odds approaching zero... Abiogenesis proponents make exactly the same mistake in reverse by claiming that, regardless of how complex the process might be, the time span involved is so incredibly huge that the probability of life arising spontaneously approaches one.

[edwino]

As I have said, I am not prepared to argue about the probability of RNA being formed, because I am not an organic chemist, and I think venturing to before descent with modification requires too many assumptions. I think arguing probabilities is futile. In terms of probability calculations, the type I have seen are of the Fred Hoyle type which I think are based on crucial misconceptions of evolution, but this is all after descent with selection. Nothing I have seen concerns the world before evolution.

But, to venture a guess, I would say that it seems that you can synthesize ribonucleic acid from a few simple organic molecules and other inorganic simple molecules like ammonia, carbon dioxide, oxygen, water, and phosphate. This is precisely what our bodies do to synthesize RNA every day. I can also imagine scenarios where some type of simpler molecule, for instance a backbone with nitrogenous bases, is able to catalyze these reactions.

Ribozymes are indeed "evolved" from other ribozymes, and at present are not capable of the complex reactions necessary to synthesize other ribonucleic acids. The field and some of the techniques to make ribozymes (SELEX) are only a few years old, though, so the fact that they have been able to make ribozymes to do what they have I think is pretty impressive.

I try to bring up Thomas Gold in these kinds of threads. His theory, from his book The Deep, Hot Biosphere is that petroleum is a feature of planet formation, not a by-product of life. He is a quite respected scientist, although not necessarily in this area, making this sentence a fallacy (argument from authority). But, he does know how to carry out an experiment, and he believes that his data support his idea. He also believes in a deep biosphere which feeds off of and regenerates the oil, and that there is a lot more oil out there than what we believe. I will say that this introduces some interesting folds to the panspermia debate, both pro and con. Pro, in terms of life not dependent on sunlight may exist in large planetismals which have warm cores and other pieces of matter ejected from a solar system. This may carry life around the universe. Con in that petroleum is a complex hydrocarbon, which could lead to all types of neat organic reactions in the proper environments. All of sudden, starting with petroleum, ribonucleic acid seems a lot easier to make.

Here is a Wired article:
http://www.wired.com/wired/archive/8.07/gold.html

As I said, I can't argue for or against panspermia. The arguments for it, though IMHO are weak because they are based on probabilities based on assumptions which are impossible to test.

[edwino]

Let me just say that I think that Miller-Urey only showed that it was easy to synthesize amino acids and peptides from ammonia, oxygen, and carbon dioxide, and so forth. I don't think that one can assume that this says anything about the early atmosphere on Earth. I will say it is compelling that such a synthesis is easy and even almost probable, because I'm sure at some point in some environment these molecules would have been around. Since amino acids and peptides are extraordinarily stable to acidic and basic environments, I think that these molecules could have stuck around for a long time, if necessary.

[Lemur866]

OK, let's stick with the panspermia angle.

I don't see how the Cambrian "explosion" can be tied to panspermia, since panspermia is supposed to occur with bacteria not metazoans.

I think the mistake you are making is emphasizing the "gradual" and "random" nature of selection. There is nothing that says that evolution should be gradual, and natural selection is anything but random.

Anyway, it's not true that all known examples of speciation have occured under artificial selection. First, define species and then we can decide whether speciation has occured or not. Let's look at dogs. We say that Chihuahuas and Great Danes are in the same species, but only because gene flow is theoretically possible via intermediate size dogs. Suppose we selected out the medium-sized dogs. Suddenly Chihuahuas and Great Danes are seperate biological species. Speciation isn't something you can detect as it is happening, only after it has happened, since the isolating factors that created two diverging populations could suddenly reverse and the isolated populations are no longer isolated.

[ACoverOfNoise]

edwino:


I don't think that one can assume that this says anything about the early atmosphere on Earth.


Correct, because there may be other mechanisms for amino acids to have formed. This is one of my central points.

In most scientific endevors, Modus Ponens logic applies:

* If it rains, then the streets will be wet.
* It is raining.
* Therefore, the streets will be wet.


Too often I see (especially in the science of biogenesis and evolution) a logical falicy called "Affirming the Consequent":

* If it's raining then the streets will be wet.
* The streets are wet.
* Therefore, it's raining.

This is the mistake that I was trying to point out to Lemur866 who wrote:


I can see no objective reason to link any codon to any amino acid, so the only explanation is that all life has a common ancestor.





Lemur866:


I don't see how the Cambrian "explosion" can be tied to panspermia, since panspermia is supposed to occur with bacteria not metazoans.


It actually requires that you make additional assumptions, but I've heard the argument made before, something along the lines of:

Assumption 1: The seed DNA is very complex with lots of non coding sequences. This would apparently not be expected, pre-Cambrian.

Assumption 2: Non coding sequences facilitate rapid evolution with certain environmental triggers.

Assumption 3: Some event or set of environmental conditions occured at the beginning of the Cambrian period to cause rapid mutation and thus great diversity in the animal population.

There's probably a lot more to the argument...



There is nothing that says that evolution should be gradual,


The theory of natural selection does explicitly state this. Certainly there are evolution theory variants that are more tolerant of rapid, macroevolutionary transitions.



and natural selection is anything but random.


In the sense that it is not a predictable process and is contingent on a multitude of varying factors... It's random in the chaos theory sort of randomness.


Anyway, it's not true that all known examples of speciation have occured under artificial selection.


I had an additional qualifier in my original statement - "observed". If you know of a counter example, I'd be interested to hear about it.



First, define species and then we can decide whether speciation has occured or not.


Ahh... herein lies the rub. There are certainly a number of definitions for "species". Most serious scientists seem to endorse Mayr's "Biological Species Concept" - reproductive isolation, for modern populations. Gould and Eldridge have suggested Punctuated Equilibria as an alternate methodology for fossil cases. PE looks at morphological, geographical, and sociological factors to make this determination. The only problem is that 100 thousand years from now a couple of scientists did up the fossil remains of your Chihuahua and your Great Dane and PE says that they would probably be classified as separate species.



Suppose we selected out the medium-sized dogs. Suddenly Chihuahuas and Great Danes are seperate biological species.


Not so. Granted it is unlikely that the gene pools would intermingle from that point on, but it's not speciation unless you want to apply PE to modern populations. I don't think Gould and Eldridge would approve of this generalization of their theory.

If, through the process of natural selection or some more radical mutation, the decendants of Chihuahuas and Great Danes were discovered to be in reproductive isolation, then we could certainly say that speciation had occured. But guess what, that speciation event could possibly occur even if the medium sized dogs were still around to facilitate gene pool intermingling.


Unless... you are maintaining that the separation is the thing that triggers the speciation event, but that is exactly my earlier point. Chihuahuas and Great Danes have been in sexual separation for thousands of years, using artificial selection techniques. This is arguably an "amplifier" of natural selection, yet no hint of biological speciation seems manifest.

But then we digress... again...