tgamble

Just had the following exchange on another board.
<a href="http://forums.sympatico.ca/WebX?14@18.IVWJaUfvEDS^11312@.1de0e93d/198" target="_blank">http://forums.sympatico.ca/WebX?14@18.IVWJaUfvEDS^11312@.1de0e93d/198</a>

Can anyone provide information on this? It sounds like he's claiming that organisims can generate abilities when needed. That's ridiculous!

Thanks for the help!

JonF

Well, certainly none of those are evidence for evolution at the organism level.

The first demonstrates that plants grow diferently under different conditions. Big surprise! There's no evidence of a permanent or hereditable change in the plant.

The second two also don't cut it, for similar reasons. They are evidence that a change occurs in a population, but this change is not necessarily due to snails "knowing" that crabs are around or barnacles "sensing" snails. They could also be due to the crabs eating all the thin-shelled snails or the straight-growing barnacles all being eaten by snails.

It's quite possible that there is a slight disadvantage to thick snail shells when no crabs are around or crooked barnacles when no snails are around, but when those predators are present the slight disadvantage is overcome by the large advantage of remaining alive. Carrying a thicker shell requires, for examaple, expending more energy on locomotion

This would lead to there always being a few thick-shell snails around in a population of mostly thin-shell snails, until the crabs show up ... then the thin-shell snails get eaten and all yuo see is thick-shell snails.

A similar argument applies to the barnacles. IIRC barnacles are filter-feeders, filtering their food from the passing currents. Bent-over barnacles are probably at a slight disadvantage in extracting their food ... but they also have a great advantage when snails are around.

Of course these are "just-so stories", just as the creationist's "evolution at the organism level" is a just-so story. The point is that his examples are not evidence that differentiates population-level evolution from organism-level evolution.

The answers to some questions could provide some differentiation. If predators are added where there were none before, do thin-shell snails grow thicker shells and straight-growing barnacles start bending over? By his thesis, they should. (And if this happens it wouldn't necessary prove his thesis; there could be some biochemical signal that just activates a dormant process). In the absense of predators, are there absolutely zero thick-shell snails and bent-over barnacles in the populations? (If evolution occurs at the population level, one would expect a few unless the disadvantage is large enought to kill them early). If predators are removed, how long does it take to recover the original population? (If organism-level evolution is true, crooked barnacles should start growing straight and thick-shell snails should start growing thin shells or even lose material from thick shells; if population-level evolution is true the descendants of the current population should reflect the makeup in the predator-not-present population {maybe in a few generations} but the individuals alive when the predators are removed would not change, unless there is a biochemical signal like I mentioned above).

pz

It's not ridiculous -- it's called physiology. Our bodies modify themselves to suit existing conditions all the time.

The examples he gave all look like they're either nonsense, or reasonably explained by expected organismal responses to the environment. What point is he trying to make?

tgamble

But we don't generate genetic changes to adapt to changeing conditions. I've seen it stated here loads of times. Evolution occurs on the population level. Isn't that why Fred Williams argument "a wolf goes into the water and drowns and that's why whales couldn't evolve" is so absurd?

That evolution occurs at the organism level according to it's need. ie. Snails (the individuals) gained the ability to make larger shells because they needed to.

Maybe I'm missing something here?

I was under the impression that evolution worked something like this. Offspring are born with variation from their parents. Some of them have advantages and such changes are spread through the population.

This guy is claim that such advantages are in response to the needs of the organism and occur at the organism level.

[ November 17, 2002: Message edited by: tgamble ]</p>

pz

Yes.
My point was that many such changes can occur at the level of the organism, and that it is nothing to contradict evolution. If you go to the gym and work out regularly, your muscles get bigger. If you work with your hands a lot, your callouses get thicker. If you move from sea level to 10,000 feet, you acquire more red blood cells.

I don't know about the details of this guy's examples, but they aren't entirely out of the realm of possibility. What they are, though, is irrelevant to the question.

Has he cited any specific references? If he isn't just making them up, it would be kind of interesting to look them up.

tgamble

Well, but such changes aren't really evolution because bigger musles and callouses aren't hereditary. Arnold's kids aren't gonna be as strong as he is. If evolution is change in a gene pool, then getting bigger muscles isn't evolution since it doesn't effect the gene pool.

Unless it makes you run faster and get away from predators. But still, the increase in strength isn't hereditable and isn't really evolution.

pz

So? Explain that to him. He's bringing up phenomena that are irrelevant to his argument.

Except...I wonder if he's playing Carl Baugh's game. Baugh is fond of claiming that if you raised modern lizards in the proper atmosphere and gravity, they'd all turn into dinosaurs. He says the atmosphere was denser and richer in O2 before the flood, and that's why people lived for a thousand years, and why those fossil species can't be found today.

tgamble

That's what I thought. Just wanted to make sure.

Doubt it. He's more of a Hugh Ross fan.

Duvenoy

It's still a population, not an indivudal. This has been observed in Canebrake Rattlesnakes (C. h. atricaudatus). Certain populations feed primarly upon frogs and have developed a 'hotter' venom due to a frog being harder to kill than a mouse.

The ability for a single individual to adapt to a different enviornment certainly exists, but it is limited and really has little, if any, effect on the evolution of the species.

If a species of snail (does this guy have any conception of how many species there are?) has a thicker shell in the presence of crabs, it is simply because the local population, NOT an individual, has, through Natural Selection, evolved a thicker shell. And, the hungry crab population is, most likely, evolving stronger claws to deal with it in the same way.

(Actually, crabs are one of the worlds most wonderful scavenger/predators. They will eat anything that they can digest, preferably carrion, which is unlikely to fight back. And they taste good, too.)

There's really not all that much that feeds on barnacles. Parrot fish do, and a few gastropods such as whelks. I'm not sure. However, the barnacle population is in no danger from the described snails ('Snail' covers a LOT of territiory).

I suggest that you call the guy on the crab/snail/barnacle nonsense and ask for documentation.

doov

Valentine Pontifex

PZ has already mentioned that physiological changes due to enviromental changes are certainly nothing new. That is, of course, not evolution. I might also point out in addition to this, this creationist is unknowingly denying microevolution. Microevolution occurs at the level of populations.