Freethought & Rationalism Archive

Keith · 02-24-2003, 01:54 PM

Quote:

Originally posted by Starboy

"Or your presumptions could be a case of trying to extrapolate too much from too little data. Not much is known about the fossil record of bats."

If the fossil record is really that insufficient for all species of bats, then we ought not assume that the fossil record provides useful and reliable information on time of development for any mammal, or any particular structure on a specific mammal. Either the fossil record can be trusted to provide such information or it can't. Are you saying it can't? If so, why is that?

Keith

Marlowe · 02-24-2003, 01:57 PM

Quote:

Yes, this is true, it isn't merely "chance." For a complex system to emerge, there has to already be information within the system. Complex systems are "information driven" systems. Such systems don't just spontaneously become complex for no reason. But this just pushes the whole thing back a few more levels. From what source did the information originate?

Actually, systems do become spontaneously complex - that's the entire point of complexity theory. And not really for no reason, but for the reason that there are a diversity of chemicals to interact. Where does chemical diversity come from? Atomic diversity - the diveristy of atoms. Where does atomic diversity come from? Quantum physics. The information you speak of is the physical structure of the universe. If you want to take things back to the Big Bang - take them there and quit hedging with evolutionary arguments.

Edit 'cause Principia came up with many more specifics on the subject of bat ears below...

Keith · 02-24-2003, 02:01 PM

Quote:

Originally posted by John Page

"Keith:

What I feel you should have posted is "Clearly, the apparent system of evolution is part of god's grand design."

Yes, I could have, and thus far I haven't said that I do, or do not believe TOE. I don't want to take the fun out of the discussion. Who knows where it will lead?

Keith

Principia · 02-24-2003, 02:13 PM

Quote:

Keith: You're getting one step ahead of me here. First, I need to hear some reason why, if the process involves PE, millions of years of time have to be required. What I'm specifically trying to get from any or all of you is a rough estimate of the time it probably took for some particular species of bat-ear to develop. It doesn't matter to me which species of bat. Even a very crude estimate would be helpful.

To develop from what? This question suggests some quantifiable transition from non-bat-ear to bat-ear, where in all likelihood that transition does not exist in black and white. But let's take one system of bat evolution under study: echolocation

Quote:

Proc. Natl. Acad. Sci. USA, Vol. 98, Issue 11, 6241-6246, May 22, 2001
Integrated fossil and molecular data reconstruct bat echolocation
Mark S. Springer,, Emma C. Teeling,�, Ole Madsen�, Michael J. Stanhope�,, and Wilfried W. de Jong

The Evolution of Echolocation. "Flight-first" (32), "echolocation-first" (33), and "tandem evolution" (34) models have been proposed to account for the evolution of powered flight and laryngeal echolocation in Chiroptera. If we accept the monophyly of Chiroptera and Microchiroptera, respectively, it follows that the flight-first hypothesis is most parsimonious with flight evolving in the common ancestor of Chiroptera and laryngeal echolocation evolving in the common ancestor of Microchiroptera. The echolocation-first and tandem evolution hypotheses become even more difficult if we accept the monophyly of Archonta because the latter disconnects the ancestry of bats from other mammalian taxa that echolocate.

In contrast, our results suggest that laryngeal echolocation, like flight, evolved before the most recent common ancestor of living and fossil taxa. Given the deployment of both flight and laryngeal echolocation to deep levels in the chiropteran tree, an additional implication is that the flight-first, echolocation-first, and tandem evolution hypotheses all remain viable. Furthermore, molecular data suggest that bats are members of the superordinal clade Laurasiatheria (16), a group that also includes eulipotyphlan insectivores such as moles and shrews. Both Eulipotyphla and Chiroptera may be early offshoots within Laurasiatheria (16, 18). Notably, some shrews in Eulipotyphla are capable of echolocation (6). The ancestry of bats may thus have a more proximal link to other mammalian taxa that echolocate. Discrimination between the flight-first, echolocation-first, and tandem evolution hypotheses may only be possible with future fossil discoveries. In any case, it now appears that the first bats were much more like Icaronycteris than previously believed.

Molecular dates presented here suggest that crown-group bats last shared an ancestor in the range of 52 to 54 million years based on the overlap of confidence intervals for individual genes and concatenations thereof. These estimates, of course, assume that the fossil calibration points are reliable. If we accept the fossil calibrations, then our molecular dates imply that key transitional fossils documenting the origin of flight and echolocation in the ancestry of living bats should be older than 52 to 54 million years. Similarly, molecular dates that were calculated by Nikaido et al. (17) suggest that flight and echolocation evolved during a 25 million year window extending from 83 million years to 58 million years.

Although laryngeal echolocation may have evolved only once in the evolutionary history of Chiroptera, there have been numerous modifications once the basic system was in place. Given the moderate size of the cochlea in the common ancestor of crown group plus fossil chiropterans, echolocation was probably a primitive type of low-duty cycle echolocation that was used for orientation and obstacle detection. Subsequent enlargement of the cochlea in Hassianycteris, Palaeochiropteryx, and living microbats resulted in sophisticated laryngeal echolocation and permitted aerial hawking rather than gleaning from a perch.

There are observations that are consistent with the hypothesis that laryngeal echolocation was lost in megabats. First, the moderately enlarged cochlea in some nonecholocating megachiropterans, which overlaps in size with the cochlea in Icaronycteris, Archaeonycteris, and some living microchiropterans (e.g., Megaderma lyra, Phyllostomus hastatus) (6, 30), may be a residual feature from this earlier stage of evolution. Second, even though living megabats do not have an expanded stylohyal, they are capable of emitting short broadband or multiharmonic FM calls in social situations such as precopulation and hostile male-male interactions (33); these calls are similar to those that microbats sometimes use in comparable social situations (33). Our reconstructions suggest that broadband or multiharmonic FM calls in megabats trace back to an ancestry in which similar calls were used in echolocation. Finally, the highly developed visual system in megabats has been viewed as a primitive feature of Chiroptera given the widespread occurrence of highly developed visual systems in other archontans including tree shrews, flying lemurs, and primates. However, molecular data consistently dissociate Chiroptera from other archontans (14-17), which suggests that the highly developed visual orientation system in megabats is an autapomorphy for this group. If the protobat did not have an enhanced visual system, as in megabats, then constraints related to brain-size (6) would have been less likely to preclude echolocation in the earliest bats.

Among megabats, a different type of echolocation, based on tongue-clicks, has been demonstrated in Rousettus (35). Given the hypothesis that laryngeal echolocation was lost in megabats, this raises the following question: Does Rousettus represent an intermediate stage in the loss of laryngeal echolocation? Molecular evidence places Rousettus as sister to an endemic African clade of megabats rather than at the base of the megabat radiation (36, 37). This phylogenetic position for Rousettus argues that echolocation was secondarily gained in this genus and is not an intermediate stage in the loss of laryngeal echolocation.

Molecular data have provided a new perspective on relationships among living bat families that has important consequences for understanding the origins of flight and echolocation in bats (15, 20). Fossil data are also of fundamental importance in reconstructing early stages in bat evolution and we agree with Simmons and Geisler (6) that Icaronycteris, Archaeonycteris, Palaeochiropteryx, and Hassianycteris provide "an unprecedented view of steps leading to a major adaptive radiation of mammals." However, consideration of these fossils jointly with molecular phylogenies alters our view of these steps. Instead of a phylogenetic placement that is basal to living and fossil microbats, Icaronycteris is basal to fossil forms as well as all extant bats, megabats included. Furthermore, Icaronycteris, Archaeonycteris, Palaeochiropteryx, and Hassianycteris constitute a paraphyletic assemblage at the base of Chiroptera. This phylogenetic arrangement, in conjunction with reconstructions for key characters in the echolocation apparatus, implies that megabats evolved from echolocating microbat ancestors and have secondarily lost laryngeal echolocation. Phylogenetic evidence supporting the hypothesis that laryngeal echolocation evolved once in bats and was subsequently lost in megabats has only emerged from a combined analysis that integrates fossils with molecular phylogenies. The incorporation of molecular phylogenetic constraints into investigations of evolutionary history should be applicable in other cases where a taxonomic group includes fossils and living taxa.

Now, given this scientific analysis, let's take that step I've been waiting for. How does this imply that evolutionary processes are intelligent and purposeful?

Quote:

If the fossil record is really that insufficient for all species of bats, then we ought not assume that the fossil record provides useful and reliable information on time of development for any mammal, or any particular structure on a specific mammal.

Keith, your logic here is deeply flawed as this generalization from a negative is rather typical of creationist arguments. Let's turn the tables around. Suppose you are trying to figure out how the bat ear developed. How would you, Keith, go about researching it?

Starboy · 02-24-2003, 02:56 PM

Quote:

Originally posted by Keith
If the fossil record is really that insufficient for all species of bats, then we ought not assume that the fossil record provides useful and reliable information on time of development for any mammal, or any particular structure on a specific mammal. Either the fossil record can be trusted to provide such information or it can't. Are you saying it can't? If so, why is that?

Keith

Keith, I am afraid I do not understand where you are coming from. If we knew and understood our surroundings both past and present there would be no need for science. We can only go on what we have learned. To toss out theories that have worked for situations where we have more data simply because information about other creatures is sketchy is at best ludicrous. The goal of science is to understand our surroundings in terms of testable explanations based on natural phenomena. It has been an outrageously successful program. I can't help but think that you have a thinly veiled agenda to promote a supernatural point of view and are confused as to the difference between science and religion (TOE and creationism).

If you want to presume that existence has a purpose and you want to think that there is good reason to assume so then your task is clear - show how creation meets the purpose. Sounds simple in principle but it is impossible in practice. In looking at the universe I am at a complete loss as to what the purpose could be. If the universe does have a purpose, it is the purpose of a creature that I am sure humans have nothing in common with. To presume to understand the mind of such a being is just nonsense. Better to work from assumptions that have a chance of getting results.

Take a quick tour of the universe and tell me if you can figure out its purpose: Powers of ten. This tour starts at 10 million light years and goes down from there. There are three orders of magnatude above this that we know about.

The problem of explaining life is just a very little tiny peice of the puzzle.

Starboy

Keith · 02-24-2003, 04:06 PM

Quote:

Originally posted by Principia

"To develop from what? This question suggests some quantifiable transition from non-bat-ear to bat-ear, where in all likelihood that transition does not exist in black and white.

Keith, your logic here is deeply flawed as this generalization from a negative is rather typical of creationist arguments. Let's turn the tables around. Suppose you are trying to figure out how the bat ear developed. How would you, Keith, go about researching it?"

This is really the problem with using phrases like "transitional fossil" isn't it? How can one say what is/isn't "transitional" if there is, in the nature of the case, no clear definition (boundary) of the non-bat to bat evolution?

How would I go about researching it? Very good question!

Keith

Principia · 02-24-2003, 04:17 PM

Quote:

Keith: This is really the problem with using phrases like "transitional fossil" isn't it? How can one say what is/isn't "transitional" if there is, in the nature of the case, no clear definition (boundary) of the non-bat to bat evolution?

Perhaps I was not clear. You asked a time frame from the development of bat-ears, but to answer that question requires a reference point. So, provide us one: are we talking about, since the beginning of the universe? the last common ancestor of bats? the last common ancestor with an auditory system? the beginning of life? Anyone of those points is considered a time point where there was, well, "no bat ears." EDIT: More to the point, if you don't accept common descent, then this question really is quite moot.

Your complaint about "transitional" fossils is odd, but informative. Will you go ahead and reveal your position on the issue, or shall we infer from the evidence thus far?

Quote:

How would I go about researching it? Very good question!

Yes it is. And to be fair, you shouldn't expect anyone to defend evolutionary theories endlessly without providing an alternative explanation yourself. So let's hear it.

Keith · 02-24-2003, 04:17 PM

Quote:

Originally posted by Marlowe

"Actually, systems do become spontaneously complex - that's the entire point of complexity theory. And not really for no reason, but for the reason that there are a diversity of chemicals to interact."

Can you give me a few examples of systems that generate their own information spontaneously, without information already existing within the system, or without information being fed into it from outside of it?

Keith

Doubting Didymus · 02-24-2003, 04:17 PM

The only such systems are evolutionary ones.

Principia · 02-24-2003, 04:19 PM

Quote:

Keith: Can you give me a few examples of systems that generate their own information spontaneously, without information already existing within the system, or without information being fed into it from outside of it?

Define information.

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02-24-2003, 04:17 PM	#79
Doubting Didymus Veteran Member Join Date: Jul 2002 Location: East Coast. Australia. Posts: 5,455	The only such systems are evolutionary ones.

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