The Early Bird: Fossils Depict Aquatic Origins of Near-Modern Birds 115 Million Years Ago

University of Pennsylvania ^ | 15 June 2006 | Staff

[b_sharp]

"If you define those "forces" as agents which limit viability, you just said what I said. If you suggest forces that DON'T limit viability, but somehow otherwise conveniently limit mutations that should occur and would be viable simply so we don't have a huge variability, I'm not sure what the point OR the mechanism would be.

Although it is silly to call the many forms of selection 'forces', calling them that does simply the language when discussing them.

Organisms tend to cluster around the point of optimum fitness given normal morphological and environmental constraints simply because it is more likely for a specific mutation to be neutral and not contribute immediately to fitness, or deleterious and quickly removed, than they are to be immediately beneficial. But yes, relative viability is the mechanism that limits variability. However, the contribution a mutation makes to viability is dependent on the environment and a change in environment can change which mutation (which is the source for new alleles) fixes in a population.

"Put another way, I see neither the point nor the operability of selection forces that don't effect viability or opportunity to succeed but still manage to prevent mutations that have occured from spreading in the population. I guess that seems like the definition of viability and opportunity -- at least that's what I was trying to cover with those terms, which I admit may not be the scientific technical terms for whatever processes you envision.

Random drift can control the frequency of an allele without viability having anything to do with it but deleterious mutations don't usually last long enough to be affected.

[FatherofFive]

MR DUCKS

Haven't seen Mr Ducks for a long time!

Thanks for posting. I still have the t-shirt somewhere.

[Lonesome in Massachussets]

It's possible that's because they were created, not evolved? ;-)

As Martin Gardner pointed out in "Fads and Fallacies in the Name of Science" over forty years ago, one can dismiss the entire fossil record, carbon-14 and all other evidence of evolution by invoking an omnipotent creator. Either life on Earth has evolved over a period of hundreds of millions of years, through changes in climate and geology, or God made a world a few thousands years ago with attributes completely consistent with the former hypothesis.

Which of the two theories you prefer probably says more about you than the validity of either theory.

[b_sharp]

The problem is in your choice of words. 'Anything can happen' is simply too broad to be accurate. It implies that evolution can get anywhere from anywhere which is simply not true. Because successful mutations generally affect a simple modification of existing genes and need to retain viability (cost is lower than or equal to benefit) some paths are not available.

[b_sharp]

"That's probably why Inuit have darker skin to absorb UV energy than say - the Zulu. O wait,...never mind.

Only if you assume that a single form of selection can affect skin colour.

Only if you assume that the sun is the only way to acquire vitamin D.

Only if you ignore the cause of "skier's tan".

[CharlesWayneCT]

"how many vertebrates are headless" is the same as "how many headless are vertebrates"

Maybe you meant "what percentage of" -- that could be different because of the different populations.

Of course, we all know that there are no headless vertebrates. In fact, if we were told a life form was headless, we would assert that it wasn't a vertebrate, and if someone showed us bones that suggested it WAS a vertebrate, but assured us there was no head, we would assume either the bones did not go together the way we thought, or the person was wrong about there not being heads.

[CharlesWayneCT]

I'm still hung up on creatures evolving from the sea to the land but then evolving back into the sea. That would seem odd until we found evidence of it, but then it must be accepted because it is observed.

If we ever FOUND a headless vertebrate, we would have to re-think our assumptions, I guess, not that I think we'll ever find such a creature. I've never met a creature who used to have a head and now doesn't but is still alive.

Of course, I've never met a creature with a half-formed head either, but I presume we must believe they existed at some point since we obviously didn't evolve an entire head with a single mutation (if we did, then one could postulate a single mutation that would reverse the process).

Oddly, we evolved a tail, and then managed to evolve it away, so it's not like we don't have evolutionary examples of body parts coming and going.

But not, I repeat again, a head. Because as I said a hundred posts ago, asking about the missing heads was a way of focusing on an issue by using an obvious example, and was in no way construable as saying that the birds in the example didn't have heads.

But it was much easier to argue that they must have had heads and it was stupid to suggest otherwise (now THAT was a strawman argument) than it was to discuss the issue of seeing what you expected to see.

[CharlesWayneCT]

That is true, the construct was overly broad (too simplistic I would argue) -- my point wasn't really about infinite possibilities so I didn't think of it that way until you mentioned it.

[webstersII]

"PROTIP: Instead of merely stating that examples exist, you should present specific cases to your reader."

Anyone on these threads for any lenth of time knows that this has been roundly discussed, besides the fact that anyone who keeps up with current events has seen this stuff in the news as well.

[Boxen]

A poor excuse. Such an attitude is a disservice to your reader.

It was only a recommendation. You wish your arguments to remain unremarkable. Who am I to stop you?

[webstersII]

"Who am I to stop you?"

I wasn't asking for your opinion anyway.