What is "Earth-like"?

[pErvinalia]

He's so far from right it's not funny. That's an opinion of what is reasonable. It's got absolutely nothing to do with logic.

[rainbow]

What we do know is that only one lineage of successful replicators emerged, and began the whole tree of life.

Either it was an incredibly rare event, and we are here by an enormous amount of sheer luck, or the first successful lineage developed such momentum that a number of other possible replicator starting points occurring later were ruthlessly crushed in infancy.

Knowing how life operates, the second rings true...

...so tigers do eat trees?

I see you are battling with the self-evidence of this.

Tigers don't eat trees because they've not evolved to produce the enzymes necessary to digest cellulose. They do not recognise it as food. Gazelles they can digest, so they recognise them as food and catch them and eat them. Even though gazelles are less plentiful and are harder to catch than trees.
All of this is so obvious that I shouldn't need to point it out.

Now if new life emerged, it would be different from existing life forms even if ever so slightly. The existing life forms would then have to evolve new metabolic paths and enzymes to take advantage of this new nutrient source. For that existing life there is a heavy investment in evolving metabolism. It is only worthwhile if there is enough feedstock. This implies that new life would actually have to establish itself before the existing life could evolve to eat it.

It really isn't that difficult a concept to grasp.

[pErvinalia]

Now if new life emerged, it would be different from existing life forms even if ever so slightly. The existing life forms would then have to evolve new metabolic paths and enzymes to take advantage of this new nutrient source.

That assumes it is different enough to require evolution. Why do you make that assumption?

[pErvinalia]

And predation isn't the only way a new species could be squeezed out. They may be unable to compete for resources in a full niche.

[rainbow]

Now if new life emerged, it would be different from existing life forms even if ever so slightly. The existing life forms would then have to evolve new metabolic paths and enzymes to take advantage of this new nutrient source.

That assumes it is different enough to require evolution. Why do you make that assumption?

There are a large number of possible combinations of C,H,O,N and P that make up the basis of biochemicals. To assume that only one set would work is the extraordinary claim.

Explain why this should be so.

Bear in mind that an amino acid that is identical to the natural l-amino acid, is completely useless to life forms if its atoms are arranged in the mirror image d-form.
http://www.phschool.com/science/biology ... landd.html

Such a small difference turns a potential food into something that life can't use. They simply did not evolve the enzymes to do so.
I assume that your organic chemistry is very weak, or you wouldn't've asked the question.

[Brian Peacock]

He's so far from right it's not funny. That's an opinion of what is reasonable. It's got absolutely nothing to do with logic.

I must take issue - as indeed you would if someone was using the aphorism to support the un-evidenced existence of God.

[pErvinalia]

That doesn't change the logical exactitude of it, though. It applies to God as well. That's why the vast majority of atheists don't maintain that God doesn't exist.

[Forty Two]

Now if new life emerged, it would be different from existing life forms even if ever so slightly. The existing life forms would then have to evolve new metabolic paths and enzymes to take advantage of this new nutrient source.

That assumes it is different enough to require evolution. Why do you make that assumption?

"different enough to require evolution." LOL.

Things must have a particular degree of difference in order to "require" evolution? What are you saying here?

[pErvinalia]

It was rainbow's claim that evolution of existing life forms would be necessary for them to eat any new life forms. Can you not read?

[Brian Peacock]

That doesn't change the logical exactitude of it, though. It applies to God as well. That's why the vast majority of atheists don't maintain that God doesn't exist.

Don't do a Seth and confuse semantic cohesion for logical exactitude, though the poetry of The Absence Aphorism is beguiling I'll grant.

I maintain that God doesn't exist, and a similar but altogether more applicable aphorism highlights why: Extraordinary claims require extraordinary evidence.

[pErvinalia]

Exactly. And that's why I mentioned it in reference to rainbow's extraordinary claim. You seem to be confused, like 42, that i've made a claim about the likelihood of abiogenesis.

[Forty Two]

It was rainbow's claim that evolution of existing life forms would be necessary for them to eat any new life forms. Can you not read?

Better than you, obviously. You may wish to evaluate your writing skills, if it's not your deficient brainpower which results in your muddled composition.

Go forth, young man, and declare that Copi can't even logic. You and a few of your friends at Ratskep know better, in this as in all things.

[pErvinalia]

Cool story, bro. And an argument from authority fallacy tacked on for good measure. You just keep wracking em up...

[Forty Two]

Err... dude... citing an authority who has made an argument is not the "argument from authority." It's the substance of Copi's material that is persuasive. Further, expert opinions on subjects are, in fact valuable, like when Lawrence Krauss lectures on physics. Copi's texts have been foundational Logic textbooks for decades, so, you may wish to take what he says seriously. Or you could just puke aphorisms you've learned on forum message boards -- next you'll be declaring as an inarguable axiom that "you can't prove a negative."

[pErvinalia]

It was an argument from authority fallacy because the bit you quoted doesn't support your contention that "absence of evidence isn't evidence of absence" isn't logical. He isn't talking about logic in the bit you quoted.