Dave Thomas posted Entry 621 on November 19, 2004 07:41 PM.
Trackback URL: http://www.pandasthumb.org/cgi-bin/mt/mt-tb.fcgi/619

Creationists and Intelligent Designists have long pointed to bats as problems for evolution, because of the general lack of transitional fossils. 

http://www.design.upenn.edu/arch/courses/MetaImages/Bats.jpg

Here’s a sample of such an argument from the dean of young-earth creationists, Duane Gish of the Institute for Creation Research:

Bats (of the order Chiroptera), the only flying mammal, are especially interesting. Evolutionists assume, of course, that bats must have evolved from a non-flying mammal. There is not one shred of evidence in the fossil record, however, to support such speculations, for, as Romer says, “Bats appear full fledged in both hemispheres in the Middle Eocene …”

And here’s an example from the dean of ID, Phillip Johnson:

It isn’t merely that grand-scale Darwinism can’t be confirmed. The evidence is positively against the theory. For example, if Darwinism is true then the bat, monkey, pig, seal, and whale all evolved in gradual adaptive stages from a primitive rodent-like predecessor. This hypothetical common ancestor must have been connected to its diverse descendants by long linking chains of transitional intermediates which in turn put out innumerable side branches. The intermediate links would have to be adaptively superior to their predecessors, and be in the process of developing the complex integrated organs required for aquatic life, flight, and so on. Fossil evidence that anything of the sort happened is thoroughly missing and in addition it is extremely difficult to imagine how the hypothetical intermediate steps could have been adaptive.

And here’s another from Johnson:

Perhaps one day scientists will be able to test some macroevolutionary mechanism, involving changes in the rate genes or whatever, that will explain how a four-footed mammal can become a whale or a bat without going through impossible intermediate steps. The difficulties should be honestly acknowledged, however.

I’m pleased to report that that “one day” has arrived.

The New Scientist reports on Nov., 13th, 2004, in an article titled Rogue finger gene got bats airborne, that

A change to a single gene allowed bats to grow wings and take to the air, a development that may explain why bats appeared so suddenly in the fossil record some 50 million years ago.

Bats have been an evolutionary enigma. That’s because the oldest fossil bats look remarkably like modern ones, each having wings formed from membranes stretched between long fingers, and ear structures designed for echolocation. No fossils of an animal intermediate between bats and their non-flying mammal ancestors have been found.

Now Karen Sears, at the University of Colorado Health Sciences Center in Denver, has discovered why intermediate forms may be missing in the fossil record. In a bid to understand where bats’ specialised finger digits evolved from, Sears compared their embryological development with that of the finger digits of mice.

Sears believes that bats began to evolve when this one gene became activated. Although it is a small developmental change, if it allowed the ancestors of bats to grow extended digits it could explain how bats evolved flight so rapidly, Sears told the Society of Vertebrate Paleontology meeting in Denver. Relatively few transitional forms would have existed just briefly before being displaced by more advanced forms.

Here’s my prediction: the ID community will be strangely silent about this new discovery.

Here’s more on this story from SciScoop:
http://www.sciscoop.com/story/2004/11/11/82718/510

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Comment #10458

Posted by Nick (Matzke) on November 19, 2004 8:09 PM (e)

Wow. That’s fairly cool. In fairness, however, to the gradualists, at most this explains how bats could evolve from a flying-squirrel-like gliding form in a relatively rapid few million years. You would still need intermediates to put together all of the various adaptations that turn a gliding mammal into a flying one. I’m sure the (itty-bitty) transitional fossils are out there somewhere in the early Cenozoic.

The fossil record of bats is in general very scarce, even though something like 1/4 of all extant mammal species are bats. Small+delicate+forest environments with acidic soils = low possibility of preservation. A summary of the bat fossil record is here.

This is interesting:

Some mammal teeth from the Paleocene of France show characters of both bats and insectivores (the group including the hedgehogs, shrews and moles of today). However, since these fossils are only teeth, we don’t know what the rest of the animal was like.

So perhaps we have some of the transitional fossils, but only the teeth.

Comment #10460

Posted by GFA on November 19, 2004 8:26 PM (e)

The abstract of their presentation from SVP:

Sears, K., Behringer, R. and Niswander, L.: THE DEVELOPMENT OF POWERED FLIGHT IN CHIROPTERA: THE MORPHOLOGIC AND GENETIC EVOLUTION OF BAT WING DIGITS

Bats suddenly appear in the fossil record roughly 50 million years ago. The earliest bats resemble their modern counterparts in possessing the anatomical hallmarks of powered flight (e.g., greatly elongated digits and interdigital membranes). To quantify these similarities, we performed a morphometric analysis of wing bones from several fossil bats and bats from all modern families. Results indicate that the lengths of the third, fourth and fifth digits (the primary supportive elements of the wing) have remained constant relative to body size for the last fifty million years. The absence of transitional forms in the fossil record forces us to look elsewhere to understand the evolution of the bat wing. With this in mind, we compared the embryological development of bat wing digits (Carollia perspicillata) with the more generalized digits of the mouse (Mus musculus) using histological and molecular techniques.

Histological results indicate that the initial cartilage condensations and segmentation patterns of bat digits are similar in size and position to those observed in mouse, suggesting that bat digit elongation is due to post-segmental developmental processes. Longitudinal growth of post-segmental digits is dependent upon the relative proliferation and differentiation of chondrocytes in the growth plate. The area in which chondrocytes undergo differentiation (hypertrophic zone) is expanded in the bat growth
plate, relative to mouse. Limb culture experiments reveal that application of the protein of a single gene, BMP2, can stimulate expansion of the hypertrophic zone in both bat and mouse digits. In addition, in situ hybridization results indicate that the expression area of BMP2 is expanded in bat digits relative to
mouse.

Taken together, these results suggest that a simple change in the spatial expression of a single key genetic regulator of limb development drove the rapid evolutionary elongation of bat wing digits. By linking small changes in molecular patterning to dramatically different phenotypes, we provide a potential explanation for the rapid evolution of bat flight.

Comment #10476

Posted by jay boilswater on November 20, 2004 3:33 PM (e)

*
“Bats are going to flop too, and everybody knows it except the bats themselves”

Will Cuppy, from “How to become Extinct”

editor’s note: for “bats” read “the ID community”

Comment #10532

Posted by Looney on November 22, 2004 2:58 PM (e)

I think Romer (or was it Colbert) which Gish quoted, did say, in effect, that if it was not for adaptations required by flight, one could just as well classify them in the order insectivora.

Said, too, that as far as dental features go, it is not particularly easy to make the order out.

There’s molecular evidence that bats originated in the cretaceous, and so on.

Comment #25527

Posted by Bill Purcell on April 18, 2005 12:52 AM (e)

To find fossil evidence of bats we would have to go back 60 or more million years. Bats are small and tend to disintegrate when they die. Their bones are small and thin, and their bodies are usually eaten and strewn by predators and scavengers. The likelihood of finding fossils sufficiently connected for identification are remote.

The only likely solution in the near future is expanded mitochondrial DNA study of the bats and the animals it might be realted to. Fossill DNA seems to be a dead end.

Bats really do exist, and as awkward as it seems, the fit somewhere in the evolution of mammals some time between 100 million years ago and 50 million years ago.

They are such lovely creatures.

Bill Purcell

Comment #25767

Posted by chris on April 19, 2005 2:53 PM (e)

“A change to a single gene allowed bats to grow wings and take to the air, a development that may explain why bats appeared so suddenly in the fossil record some 50 million years ago.

Bats have been an evolutionary enigma. That’s because the oldest fossil bats look remarkably like modern ones, each having wings formed from membranes stretched between long fingers, and ear structures designed for echolocation. No fossils of an animal intermediate between bats and their non-flying mammal ancestors have been found.”

So they appeared in the fossil record suddenly, they look remarkably like modern bats, and there are no intermediate fossils? Sounds like proof of evolution to me.
ARE YOU JOKING?!

Comment #25806

Posted by Dave Thomas on April 19, 2005 4:57 PM (e)

Syntax Error: mismatched tag 'b'

Comment #26473

Posted by Ryan on April 24, 2005 4:33 AM (e)

OK…well, first off, it is noted that this whole ordeal is an AD HOC explanation to the lack of data offered by the fossil record. No concrete data has been found genetically as far as I can read, and the problem of WHAT survival advantage a mouse with elongated arms but no ability to fly would have. Without FLYING ADAPTIVE musculatory systems ALREADY in place, growing these elongated digits doesn’t amount to squat. A mouse that can’t fly nor walk correctly doesn’t make it, nor does this article explain how sonar developed in this organism…sonar is already fully developed and ready for use in the earliest bat fossils. Ultimately, this say so story, EVEN IF GRANTED, doesn’t explain diddly…thanks for playin though.

Comment #29399

Posted by Simon Durrant on May 11, 2005 7:04 AM (e)

Hi, stumbled upon this courtesy of Google… Surely the point about the evolution of bats is that they are specialised in so many ways - not just flight, but echo-location and life upside-down for instance. The real question is how a not-yet-a-bat could be viable, isn’t it? This suggestion of a single gene that explains one part of that process is interesting, but hardly the knockdown argument you make it out to be. Surely, all that can be said it that we don’t really know.

Comment #30647

Posted by Bayesian Bouffant, FCD on May 17, 2005 11:17 AM (e)

Hi, stumbled upon this courtesy of Google … Surely the point about the evolution of bats is that they are specialised in so many ways - not just flight, but echo-location and life upside-down for instance. The real question is how a not-yet-a-bat could be viable, isn’t it? This suggestion of a single gene that explains one part of that process is interesting, but hardly the knockdown argument you make it out to be. Surely, all that can be said it that we don’t really know.

Stop calling me Surely!

Not all bats have echolocation. tropical fruit bats fly in the daytime and eat, you’ll never guess - fruit.

Of course there are things we don’t know. That doesn’t mean that we will always not know them, or that it gives us an excuse to believe in fairy tales to fill in the gaps of our knowledge.

Comment #44021

Posted by David on August 19, 2005 6:41 PM (e)

It seems odd that the sudden appearance of bats as nearly identical in form to modern ones (nevertheless they do display some primitive features) would be taken as evidence against evolution anyway. Are we to believe that bats are one of the few exceptions that make the case for creation when so many other animal lines show transitional fossils? Why should bats be excepted from evolution? If all or most other lines of animals are known to have evolved why should we not reasonably conclude bats also evolved, even if their evolutionary fossil record does not (yet) prove it?
But of course creationists claim all the transitional forms we do know of are not transitional forms, even if they look transitional. So why even bother pointing out the lack of transitions for bats? If we ever do find the earliest ancestral forms of bats and they look transitional between non-flying and flying animals, the creationists will just claim they aren’t transitions anyway. They’ve done this with such clear-cut cases as horses, icthyosaurs, amphibians, mammal-like reptiles, “dino-birds,” etc.
In response to post 26473 by Ryan, I don’t see that the presence of the elongated finger would argue against adaptation as it may have been followed by or been accompanied by a skin membrane on its way to being as well developed as a flying squirrel’s. It would be incrementally advantageous to slowing a proto-bat’s fall from the trees and could be improved in slight incremental steps for gliding. From there, as it is being shown in bird fossils, further increments would lead to flapping flight.
I recall that creationists also pointed to the sudden appearance of whales fully adapted to total marine life as an example refuting evolution. Now we have whale fossils clearly transitional between terrestrial and marine. Now the creationists say those aren’t really transitions. So it doesn’t matter what solid evidence you uncover. The creationists always wriggle out of conviction with their own ad hoc objections.