jeff@censor.UUCP (Jeff Hunter) (03/13/89)
Hello there. I was having a conversation with a friend recently, and
the question came up "Why do all birds have beaks?". I finally concluded
that somewhere just after archeopteryx there was an overwhelmingly successful
bird that ate nuts (or had some other compelling reason to lose teeth and
get a beak). Subsequent generations of birds got their beaks by inheritence,
and were able to modify them to different tasks rather than having to
re-develop teeth. Alec instead concluded that beaks have some advantage for
feeding if you've lost your forepaws ('cause they're wings).
So what are the net.opinions. (Please note that I'm crossposting this
to sci.bio, and talk.origins. If your reply doesn't have much to do with biology
please edit out sci.bio in your message. (And flame me by e-mail, if you wish,
for the previous sentence. Don't post to the net.))
Another topic in the conversation was "What are beaks made of?" This
is in the sense that rhinoceros horn is made of compressed hair, or human
fingernails are modified hair. So are beaks modified bone, cartilage, hair,
feathers, horn, or does the question make sense at all?
Thanks for the thoughts ...
--
___ __ __ {utzoo,lsuc}!censor!jeff (416-595-2705)
/ / /) / ) -- my opinions --
-/ _ -/- /- No one born with a mouth and a need is innocent.
(__/ (/_/ _/_ Greg Bear sabol@Apple.COM (Bryan Sabol) (03/14/89)
In article <404@censor.UUCP> jeff@censor.UUCP (Jeff Hunter) writes: >Hello there. I was having a conversation with a friend recently, and >the question came up "Why do all birds have beaks?". I finally concluded >that somewhere just after archeopteryx there was an overwhelmingly successful >bird that ate nuts (or had some other compelling reason to lose teeth and >get a beak). Subsequent generations of birds got their beaks by inheritence, >and were able to modify them to different tasks rather than having to >re-develop teeth. Alec instead concluded that beaks have some advantage for >feeding if you've lost your forepaws ('cause they're wings). I must admit that ornithology isn't my specialty, but if I remember a prof's theory correctly, she thought that the beak was developed as a means to lessen the bird's overall mass. To be able to fly, ancestral birds needed to modify existing structures to lighten their bodies, yet retain similar function with these adaptations. A good example would be their bone structure. All (flying) birds have hollow bones, with a lattice-work or gird-like structure, giving them strength without the much greater mass of standard solid bones. The beak was a sophisticated modification that enabled birds to rid themselves of the great amount of weight which is associated with teeth and their supporting structures. Though the teeth themselves aren't what comprise great mass, the supporting structures associated with teeth *are* massive. Note, for example, the size of many predators' skulls: the size and weight of the bones which are supporting the teeth are very large. To operate teeth, one must also have a strong jaw which houses the teeth. Then one needs more thick bones to support the large muscles needed to operate the jaw: the development of cranial ridges was expressly for the operation of these powerful jaws. (Also, these large cranial ridges are not unique to one type of food source; they can be found in both carniverous [e.g., wolf] animals, used to tear flesh from bone, and in herbiverous [e.g., mountain gorilla] animals, to help grind up leaves.) So, if an animal wanted to considerablely lessen its total mass without losing the function of said massive structures, a beak would be a particularly good development. Beaks are strong, light, and weigh very little. The one thing they can't do is chew food, so the addition of a few pebbles, etc., to a gizzard does the job. The beak made the large jaw, and the large bones which support the muscles to operate the jaw, unnecessary. Finally, I would argue against your friend's theory of beaks developing because of no front limbs (or, at least, modified into wings). If this were true, then we could expect to see snakes with beaks. Or maybe some bats would, too (since the snake has no front limbs, and the bat has wings). I would further say that though the beak seems to do very well as a food-gathering device, it wouldn't be the best thing to have, over all other structures. It's rigidity makes some types of food almost impossible to get. Take, for example, one of the finches that Darwin first discovered in the Galapagos islands, which feeds on grubs underneath the bark of trees. The finch had to get ahold of a sharp stick or needle, and, holding it in its beak, use the needle to probe for the grubs. True, this is a relatively new adaptation, and we may find, thousands/millions of years down the road, that the bird has develped a beak more similar to a woodpecker's. Other ideas? Flames? bryan sabol anemoneman and ousted reedie-at-large
sparks@corpane.UUCP (John Sparks) (03/21/89)
In article <27216@apple.Apple.COM>, sabol@Apple.COM (Bryan Sabol) writes:
] To be able to fly, ancestral birds needed to modify existing
] structures to lighten their bodies, yet retain similar function with
] these adaptations.
] ...
] The beak was a sophisticated modification that enabled birds to
] rid themselves of the great amount of weight which is associated with
] teeth and their supporting structures.
] [explanation about support structure needed to have teeth. ]
] [cranial ridges, jaws, jaw muscles etc -deleted for space ]
]
] So, if an animal wanted to considerablely lessen its total mass
] without losing the function of said massive structures, a beak would be
] a particularly good development. Beaks are strong, light, and weigh
] very little. The one thing they can't do is chew food, so the addition
] of a few pebbles, etc., to a gizzard does the job. The beak made the
] large jaw, and the large bones which support the muscles to operate the
] jaw, unnecessary.
]
] Finally, I would argue against your friend's theory of beaks
] developing because of no front limbs (or, at least, modified into
] wings). If this were true, then we could expect to see snakes with
] beaks. Or maybe some bats would, too (since the snake has no front
] limbs, and the bat has wings).
Your arguement seems to break up for me here. You use the fact that snakes
and bats don't have front limbs and no beaks, to show that birds did not
develop beaks just because they don't have front limbs (just wings). What
does one have to do with the other? Snakes and bats aren't birds. Different
animals have evolved differently from the same stimuli.
If all animals evolved simularly from the same environmental pressures, I could
use your arguement to ask you then, since bats and some birds both have wings
and eat the same diet, why don't bats have beaks? Don't they have
to save weight? Why do they have teeth? Jaws and such? Why do penguins have
beaks? They can't fly. So no need to save weight there. Do penguins have teeth?
I believe they do. What is the air speed velocity of a swallow?
Enquiring minds want to know!!!
--
John Sparks | {rutgers|uunet}!ukma!corpane!sparks | D.I.S.K. 24hrs 1200bps
______________| sparks@corpane.UUCP | 502/968-5401 thru -5406
If we weren't supposed to juggle, tennis balls wouldn't come three to a can.sabol@Apple.COM (Bryan Sabol) (03/24/89)
In article <464@corpane.UUCP> sparks@corpane.UUCP (John Sparks) writes: >Your arguement seems to break up for me here. You use the fact that snakes >and bats don't have front limbs and no beaks, to show that birds did not >develop beaks just because they don't have front limbs (just wings). What >does one have to do with the other? Snakes and bats aren't birds. Different >animals have evolved differently from the same stimuli. What I was trying to say is that I don't believe one can correctly hypothesize that birds developed beaks *solely* because they had wings/didn't have forelimbs. While I agree that the absence of forelimbs may have assisted the development of such a novel item as the beak, I would say that it would be a secondary developmental pressure at best. Much more important to the beak's development was the loss of body mass (see the previous article). So my (albeit extreme) examples of the snakes and bats was to say that 1) the absence of limbs (as in the snake) didn't promote beak development in and of itself, and 2) the ability to fly (such as bats) also doesn't necessitate the development of a beak. >If all animals evolved simularly from the same environmental pressures, I could >use your arguement to ask you then, since bats and some birds both have wings >and eat the same diet, why don't bats have beaks? This really is an innaccurate statement from the onset. First, depending upon the species, birds have an incredibly varied diet. The same goes for bats: there are insect-eating bats, fruit-eating bats, fish-catching bats, and, of course, the vampire bats, which subsist on a diet of (mainly) cattle blood. Each different diet reflects modifications in the animal's eating apparatus. Next, I definately agree with what you said about similar evolutionary pressures: I would say that the reason that bats don't have beaks is that they are not birds. Simple, but true. The beak was a development started by one group of organisms approx. 150 million years ago (_archeopteryx_ is generally agreed to be the earliest/best evidence). A very popular evolutionary theory is called "parallel evolution", which means that animals with quite different ancestors, but living in the same environment, will develop along similar lines. The important idea here is that though the different animals may look and function similarly, this doesn't dictate that they will develop the same anatomy/structures. A very good example is the shark vs. the killer whale: very different animals, with very different apparatae: one has gills, the other lungs. One is cold-blooded, the other warm-blooded. One completed its evolutionary development roughly 250+ million years ago; the other is barely 50+ million years old. >Don't they [bats] have to save weight? Why do they have teeth? Jaws and >such? Why do penguins have beaks? They can't fly. So no need to save weight >there. Do penguins have teeth? I believe they do. Yes, to be able to fly, the bat's evolutionary development required them to lose weight. Again, according to the parallel evolutionary theory, the bats didn't *have* to develop beaks; they *did* have to find some way of lessening their total mass. What I'm trying to say is that the beak was a great development which lessened the total mass of an animal -- but it isn't/wasn't the *only* way to lose mass. The bat is such an example. I don't know why bats retained all the teeth/jaw apparatus and still are able to fly. I'd be interested to hear of ideas. One guess is that they lessened the total mass of their jaws as much as possible, and they also may have a much lower glide ratio than the average flying bird. No, penguins do not have teeth. They do have serrated edges along their beaks, but no teeth. If you look at the skeletal structure of a penguin, you'd be amazed at their mass. They have, as a genus/species, been "grounded" for millions of years, which has enabled them to develop more along the lines of a seal/dolphin/etc. than what one would normally consider a bird. Penguins still have beaks because they come from the same ancestory as all birds. As I mentioned before, the beak is a very useful tool, and the penguins have adapted it to their marine feeding techniques. Think of it this way: it's much easier for an animal to adapt an existing structure than it is to develop a totally new one. The beak was a new type of structure, and this is one of the reasons why I believe it hasn't appeared in any other life form: it's quite unique. So, penguins have retained their beaks since it's easier to modify what they already have (i.e., a beak) than it would be for them to lose a beak and once again develop teeth/jaws. Ergo, we see a thick, heavy bill, with sharp serrations along the edges. Just right for catching fish/squid. >What is the air speed velocity of a swallow? What do you mean? European or African? bryan sabol ousted reedie-at-large
sparks@corpane.UUCP (John Sparks) (03/25/89)
<27761@apple.Apple.COM> In article <27761@apple.Apple.COM>, sabol@Apple.COM (Bryan Sabol) writes: > In article <464@corpane.UUCP> sparks@corpane.UUCP (John Sparks) writes: > > >What is the air speed velocity of a swallow? > > What do you mean? European or African? > > bryan sabol > ousted reedie-at-large > > I don't know... AAAAAA AAAA AAEEE E E E . . .
jeff@censor.UUCP (Jeff Hunter) (04/01/89)
In article <27761@apple.Apple.COM>, sabol@Apple.COM (Bryan Sabol) writes: > Much more important to the beak's development was the loss of body mass > ... > birds have an incredibly varied diet. The same goes > for bats: there are insect-eating bats, fruit-eating bats, fish-catching bats, > and, of course, the vampire bats, which subsist on a diet of (mainly) cattle > blood. Each different diet reflects modifications in the animal's eating > apparatus. > ... > I don't know why bats retained all the teeth/jaw apparatus and > still are able to fly. I'd be interested to hear of ideas. Hmmmm. Well if you look at the range of bat-foods they all look soft (except maybe the cattle). If bats went in for eating nuts or bone marrow they'd need pretty hefty jaws (and maybe little anti-grav packs too :-). So I'm going to repeat my guess that early birds ate nuts (and needed a lightweight nutcracker, and were overwhemingly successful). As a side note I seem to recall a short, fat, shelled four-legged snake with a beak. (Okay, okay, I know turtles aren't even close to being snakes. Call it post-tistic licence.) Do turtles hide teeth back there in their beaks? Anyone know? -- ___ __ __ {utzoo,lsuc}!censor!jeff (416-595-2705) / / /) / ) -- my opinions -- -/ _ -/- /- No one born with a mouth and a need is innocent. (__/ (/_/ _/_ Greg Bear
sabol@Apple.COM (Bryan Sabol) (04/04/89)
In article <454@censor.UUCP> jeff@censor.UUCP (Jeff Hunter) writes: >Hmmmm. Well if you look at the range of bat-foods they all look soft >(except maybe the cattle). If bats went in for eating nuts or bone marrow >they'd need pretty hefty jaws (and maybe little anti-grav packs too :-). >So I'm going to repeat my guess that early birds ate nuts (and needed >a lightweight nutcracker, and were overwhemingly successful). I think we've got a problem with that idea: if I remember correctly, we both agreed that _archeopteryx_ is considered to be the first/ancestoral bird, yet its diet was small animals and insects. I'm pretty sure that its diet wasn't vegetarian. I do agree that birds were successful; seeing their numbers and diversity 150 million years later is testimony to that. My question is though, how does the success of birds relate to beaks/wings? I lost the point of your aforenoted statement somewhere. >As a side note I seem to recall a short, fat, shelled four-legged >snake with a beak. (Okay, okay, I know turtles aren't even close to being >snakes. Call it post-tistic licence.) >Do turtles hide teeth back there in their beaks? Anyone know? Yup. I think that turtles have true beaks. There are also some fish who also have beaks (generically called 'parrotfish', for good reason), too. I wasn't arguing that birds were the only animals at all to have beaks; I guess a better clarification would be to say that I can't think of another order (I think that's the correct level) of organisms that *only* have beaks. Finally, we all know what the perfect answer is (42); it's the question that needs to be found (beware of mouse). bryan sabol ousted reedie-at-large
jwm@aplvax.jhuapl.edu (Jim Meritt) (04/04/89)
I believe "Why does __________ have _________?" is a creationists issue. It is implying design FOR something. The selection process, as I understand it, does not go FOR something but removes things that are less optimal for the immediate surroundings than other existant forms (unless that particular form is non-viable all on its own). The evolutionists question would be "Why does ________ not have _______?". This would be a search for why that feature was NOT selected. Disclaimer: "It's mine! All mine!!!" - D. Duck
sabol@Apple.COM (Bryan Sabol) (04/05/89)
In article <3561@aplcomm.jhuapl.edu> jwm@aplvax.jhuapl.edu.UUCP (Jim Meritt) writes: >I believe "Why does __________ have _________?" is a creationists issue. >It is implying design FOR something. "Creationist's"? Oh, PLEASE! Let's not start that! >The selection process, as I understand it, does not go FOR something but >removes things that are less optimal for the immediate surroundings than >other existant forms (unless that particular form is non-viable all on its >own). The evolutionists question would be "Why does ________ not have >_______?". This would be a search for why that feature was NOT selected. I think you're really mincing words here: selection is selection. Try this: environmental pressure upon a species will be more beneficial towards certain individuals, due to an advantageous trait. For example: a giraffe with a long neck can eat all the leaves that a giraffe with a short neck can eat, plus more leaves out of the latter's reach. This pressure would give this giraffe a better chance to survive and rear its young; therefore adding "long-neckedness" to the giraffe's gene pool. Now, I could argue that the giraffes of today's time have long necks due to intraspecies competition for leaves on trees: the longer-necked ones could eat more leaves. This is a "Why does ______ have _______" statement. Or, I could say that giraffes don't have short necks due to the intraspecies competition for leaves on tress: the shorter-necked ones had to eat the leaves lower-down on the trees, where all the individuals could eat. This is a "Why does _______ not have _______?" statement. The two statements are equally valid; they're just looking at the same evolutionary process from a positive-attribute and negative-attribute standpoint, respectively. Finally, I would caution you to take a look at your original posting of "birds & beaks: >In article <404@censor.UUCP> jeff@censor.UUCP (Jeff Hunter) writes: >>Hello there. I was having a conversation with a friend recently, and >>the question came up "Why do all birds have beaks?". ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ("Ooops," I'd expect... :-b ) Ever lovin' bryan sabol ousted reedie-at-large
kaufman@maxzilla.Encore.COM (Lar Kaufman) (04/05/89)
The general tone of speculation on this topic has been tiresome and given to uninformed speculation. It has included assertions of opinion as fact, irrelevant analogies, and poor reasoning. How about dropping it, OK? At least leave sci.bio out of it. -lar "It's about a man, two women, and a revolution. What could be simpler than that?" - Roger Ebert Lar Kaufman <= my opinions kaufman@Encore.com
jeff@censor.UUCP (Jeff Hunter) (04/05/89)
In article <28330@apple.Apple.COM>, sabol@Apple.COM (Bryan Sabol) writes: > In article <454@censor.UUCP> jeff@censor.UUCP (Jeff Hunter) writes: > >So I'm going to repeat my guess that early birds ate nuts (and needed > >a lightweight nutcracker, and were overwhemingly successful). > > I think we've got a problem with that idea: if I remember > correctly, we both agreed that _archeopteryx_ is considered to be the > first/ancestoral bird, yet its diet was small animals and insects. I'm > pretty sure that its diet wasn't vegetarian. > I do agree that birds were successful; seeing their numbers and > diversity 150 million years later is testimony to that. My question is > though, how does the success of birds relate to beaks/wings? I lost the > point of your aforenoted statement somewhere. Sure. I'll try to make it clearer. - bats eat soft stuff therefore bats can get away with small sharp teeth, and small lightweight jaws - if bats had to eat something that required a heavier jaw they'd either a) become flightless or b) develop beaks (or c) starve). - archeopteryx ate soft stuff (insects & small animals). It had small sharp teeth. - ALL modern birds have beaks - therefore I conclude (and I know it's tenuous) that some near descendants of archeopteryx ate something that needed a strong jaw (my guess "nuts"). They developed beaks. They then were successful enough to overwhelm all the (left-over) toothed birds. -- ___ __ __ {utzoo,lsuc}!censor!jeff (416-595-2705) / / /) / ) -- my opinions -- -/ _ -/- /- No one born with a mouth and a need is innocent. (__/ (/_/ _/_ Greg Bear
jwm@aplvax.jhuapl.edu (Jim Meritt) (04/05/89)
In article <28379@apple.Apple.COM> sabol@Apple.COM (Bryan Sabol) writes: }In article <3561@aplcomm.jhuapl.edu> jwm@aplvax.jhuapl.edu.UUCP (Jim Meritt) writes: }>I believe "Why does __________ have _________?" is a creationists issue. }>It is implying design FOR something. } } "Creationist's"? Oh, PLEASE! Let's not start that! Then why did you cross-post to talk.origins? }>The selection process, as I understand it, does not go FOR something but }>removes things that are less optimal for the immediate surroundings than }>other existant forms (unless that particular form is non-viable all on its }>own). The evolutionists question would be "Why does ________ not have }>_______?". This would be a search for why that feature was NOT selected. } } I think you're really mincing words here: selection is }selection. Try this: environmental pressure upon a species will be }more beneficial towards certain individuals, due to an advantageous }trait. I don't thinkI am mincing words. I am using words in a manner that matches the process. The original mutations are not selective. At least _I_ don't think that the organism mutates itself towards a goal. (Mary? I read that some bacteria do this?) The filter that does the selection removes things. Therefore, the filter selects "why not". A trait that is not selected against continues. example: Do you have blue, brown, green,, or other eyes? } The two statements are equally valid; they're just looking at }the same evolutionary process from a positive-attribute and }negative-attribute standpoint, respectively. Yes, but one better describes the processes concerned and the other merely observes the results. } Finally, I would caution you to take a look at your original }posting of "birds & beaks: I suggest that you read attributes. My posting was the first that I have done on what I consider an odd topic. }>In article <404@censor.UUCP> jeff@censor.UUCP (Jeff Hunter) writes: ^^^^^^^^^^^^ } >>Hello there. I was having a conversation with a friend recently, and }>>the question came up "Why do all birds have beaks?". Answer: "Why not? Non-birds also have beaks." Disclaimer: "It's mine! All mine!!!" - D. Duck
sabol@Apple.COM (Bryan Sabol) (04/06/89)
In article <471@censor.UUCP> jeff@censor.UUCP (Jeff Hunter) writes: >Sure. I'll try to make it clearer. >- bats eat soft stuff therefore bats can get away with small sharp teeth, >and small lightweight jaws >- if bats had to eat something that required a heavier jaw they'd either >a) become flightless or b) develop beaks (or c) starve). > >- archeopteryx ate soft stuff (insects & small animals). It had small >sharp teeth. >- ALL modern birds have beaks > >- therefore I conclude (and I know it's tenuous) that some near descendants >of archeopteryx ate something that needed a strong jaw (my guess "nuts"). >They developed beaks. They then were successful enough to overwhelm all >the (left-over) toothed birds. Okay, I'll go along with that; it seems more plausible than connecting the necessity of beak expressly to wing. bryan sabol ousted reedie-at-large
sabol@Apple.COM (Bryan Sabol) (04/06/89)
In article <3566@aplcomm.jhuapl.edu> jwm@aplvax.jhuapl.edu.UUCP (Jim Meritt) writes: In article <28379@apple.Apple.COM> sabol@Apple.COM (Bryan Sabol) writes: >} "Creationist's"? Oh, PLEASE! Let's not start that! > >Then why did you cross-post to talk.origins? Whoops. 'twasn't intentional. I was responding via sci.bio, and, due to the course of the dialog, was hoping to keep it to the developmental realm. >I don't thinkI am mincing words. I am using words in a manner that matches >the process. The original mutations are not selective. At least _I_ don't >think that the organism mutates itself towards a goal. (Mary? I read that >some bacteria do this?) The filter that does the selection removes things. >Therefore, the filter selects "why not". A trait that is not selected against >continues. example: Do you have blue, brown, green,, or other eyes? I'm not sure what you mean by this. Mutations are much more commonly deleterious than advantageous. If a mutation is deleterious, then an organism will have a lesser chance of survival than a 'normal' organism, and one could gather that the same mutated organism would have a much less chance of survival than one who had an advantageous mutation. It is true that "a trait that is not selected against continues", but neither does it change. Without the advantageous mutations, the population/species would never change, and therefore no new species would develop at all (such as modern birds from _archeoptyrx_). So, if you really wanted to be specific about how you phrase the process, it would be more accurate to say that the filter that "does the selection" removes the deleterious mutations, but the manner (at least for this arguement) in which new species develop would be from advantageous mutations. Therefore, one should say "why does ___ have ___", and not "why doesn't ___ have ___". >} Finally, I would caution you to take a look at your original >}posting of "birds & beaks: > >I suggest that you read attributes. My posting was the first that I have >done on what I consider an odd topic. > >}>In article <404@censor.UUCP> jeff@censor.UUCP (Jeff Hunter) writes: ^^^^^^^^^^^^ Mmmmmrphhh (Trans: "oops", with my foot in my mouth :-b ) bryan sabol ousted reedie-at-large
djones@megatest.UUCP (Dave Jones) (04/06/89)
From article <28434@apple.Apple.COM>, by sabol@Apple.COM (Bryan Sabol): [ ... ] > Without the advantageous > mutations, the population/species would never change, and therefore no > new species would develop at all .... When you say "mutation", I presume you include mutations due to transfer of genetic material by viruses?
jwm@stdc.jhuapl.edu (Jim Meritt) (04/06/89)
In article <28434@apple.Apple.COM> sabol@Apple.COM (Bryan Sabol) writes: }In article <3566@aplcomm.jhuapl.edu> jwm@aplvax.jhuapl.edu.UUCP (Jim Meritt) writes: }>I don't thinkI am mincing words. I am using words in a manner that matches }>the process. The original mutations are not selective. At least _I_ don't }>think that the organism mutates itself towards a goal. (Mary? I read that }>some bacteria do this?) The filter that does the selection removes things. }>Therefore, the filter selects "why not". A trait that is not selected against }>continues. example: Do you have blue, brown, green,, or other eyes? } } I'm not sure what you mean by this. Mutations are much more }commonly deleterious than advantageous. If a mutation is deleterious, }then an organism will have a lesser chance of survival than a 'normal' }organism, and one could gather that the same mutated organism would have }a much less chance of survival than one who had an advantageous }mutation. } It is true that "a trait that is not selected against }continues", but neither does it change. Without the advantageous }mutations, the population/species would never change, and therefore no }new species would develop at all (such as modern birds from _archeoptyrx_). }So, if you really wanted to be specific about how you phrase the process, it }would be more accurate to say that the filter that "does the selection" }removes the deleterious mutations, but the manner (at least for this }arguement) in which new species develop would be from advantageous }mutations. Therefore, one should say "why does ___ have ___", and not }"why doesn't ___ have ___". Precisely. The "Why is this here?" initially is random mutation. For the first occurrance it would be a spontaneous event without particular reason. The "Why is this here?" for a trait which is passed down is because it has not been removed. If the trait is of minimal impact, it will remain (even though its origins were totally random) so "why is it here?" is not especially informative. As per the example of eye color. A trait which is of negative impact will probably disappear. (note: probably does not mean will eventually, or even will at all) IF the distribution of "adaptiveness" is random (due to the variance from those random mutations being stirred around) and the tail of the distribution is continuously being chopped off (by natural selection) the mean will slowly creap up to the max. If the variance is continuously being forced upon the system (by the spontaneous mutations) at a rate such that the new "tail" is smaller than the old "tail" (deliterious mutations do not exceed the number selected against) the distribution will shift upward. There are two processes: one random (mutation) that really doesn't have a reasonable "why?" aside from luck, and selection that has a "Why?" that is really a "Why not?" that selectively removes the tail. _TWO_ processes are required. One can be (appears to be) random, and the other a selection process on the distribution. "Why?" should not have the answer "luck?" unless that is the answer, and it is not (strictly) Doc Terry - if you are still doing your attempts at ecosystem modelling, try generating a random selection of numbers. Calculate the mean. Remove the lowest 5%. Add a random value to each number (-/+ small value). Calculate the mean. Remove the lowest 5%.... What is the trend of the mean over generations? Try with varying elemination percentages and magnitude of change. The above was test data, and not the responsibility of any organization.
sabol@Apple.COM (Bryan Sabol) (04/06/89)
In article <3318@goofy.megatest.UUCP> djones@megatest.UUCP (Dave Jones) writes: >From article <28434@apple.Apple.COM>, by sabol@Apple.COM (Bryan Sabol): >[ ... ] >> Without the advantageous >> mutations, the population/species would never change, and therefore no >> new species would develop at all .... > >When you say "mutation", I presume you include mutations due to >transfer of genetic material by viruses? Sure. A mutation, caused by faulty sequencing of an individual's own cellular division, or caused by radiation, or by virus, or whatever. I wasn't terribly interested in what the source of the mutation was, only what the result was. If the virus' transciption resulted in a adventageous mutation, then the argument remains the same. bryan sabol ousted reedie-at-large
aj-mberg@dasys1.UUCP (Micha Berger) (04/07/89)
> As a side note I seem to recall a short, fat, shelled four-legged > snake with a beak. (Okay, okay, I know turtles aren't even close to being > snakes. Call it post-tistic licence.) If turtles DO have a beak, this bring up a sore point in Evolutionary theory -convergences. Anyone want to build up odds that to phyla solved a problem exactly the same way? Ever look into an octapus eye lately? Micha Berger -- Micha Berger Disclaimer: All opinions expressed here are my own. The spelling, noone's. email: ...!cmcl2!phri!dasys1!aj-mberg Aspaklaria Publications vox: (718) 380-7572 73-32 173 St, Hillcrest, NY 11366
cjm@reed.UUCP (Chris Marshall) (04/07/89)
Bryan, I've been following your discussion for a week or so and have had a problem with the question you are addressing. The original question of "why do birds have beaks? which is analogous to many other questions regarding a variety of character traits in an array of organism such as you pointed out with your giraffe example of "why do giraffes have long necks". The problem with these sorts of questions is that the question is not clear enough. Are you refering to what evolutionary issues caused beaks to become prevalent in birds, or are you discussing what current environmental cirumstances exist such that beaks are a favorable trait? the two question are quite different, and have I think resulted in the general dismay that other readers have voiced concerning the discussion in general. Is it truely possible to show that beaks are an adaptive trait which arose due to specific selective forces favoring them; specifically flight? An example of what I'm trying to say can be seen in the case of artic animals such as the arctic fox. In looking at the arctic fox one notes that its ears are much smaller than its more temperate cousins. From this one might be led to the question of why do arctic foxes have small ears? Once doing so, the investigator can then proceed to make observations, do experiments and such in order to examine the roll of the smaller ears within the arctic environment. He/She may come to the conclusion that the small ears grant the fox an advantage in cold environments because of reduced heat loss. So, then is it correct to assume that small ears arose over evolutionary time because of natural selection's favoring of small ears in foxes? The answer is no. This does not necessarily follow as the small ears could have arisen for a variety of non-adaptive factors and was subsequently maintained in the population because of the proximate effects of the environment. However, all is not lost, for studies investigating ear size in other organisms also show that reduced ear size is correlated to colder conditions (arctic rabbits and wolves show a similar phenomenon). This tends to give more support to the claim that small ears are an adaptive trait, but still doesn't prove it. The question then arises as to how much evidence needs to be given in order to show that a trait is adaptive? Obviously your disscussion has shown that very little evidence indeed needs to be given in order to "prove" the adaptive nature of beaks for many people. In fact many people are happy to accept just about any adaptationist story about any organism, including humans. Thus, we have a large mass of fun nature stories concerning "why this" and "why that". I am not, I have to state, undermining adaptation as a fundamental evolutionary process, however, I think that under many cases, such as birds and beaks, it is not possible to provide the answer. As in the above case of ears, there are a vast array of organisms which live in both cold and warm environments. Such comparisons are not as easy in your case, comparison to bats is close to this, but there just isn't enough other animals to compare with. The other approach which would be analogous to comparing all the animals with small ears to check for environmental similarities...such as your comparison to parrot fish and turtles are equally unconvincing. A good article to read would be Gould and Vrba (1982) "Exaption--a missing term in the science of form", Paleobiology, 8(1):pp4-15. It goes through this issue as well. I wish you luck in finding out the definitive answer to your question...but in truth I think it will ultimately depend on what you consider to be "definitive". Maybe a better question would be: "Why are humans so obsessed with the question of why birds have beaks?" please respond via mail- (I tried to mail this letter to you but somehow it bounced back) -chris marshall
gsh7w@astsun1.acc.Virginia.EDU (Greg Hennessy) (04/07/89)
In article <9229@dasys1.UUCP> aj-mberg@dasys1.UUCP (Micha Berger) writes:
# If turtles DO have a beak, this bring up a sore point in Evolutionary
#theory -convergences. Anyone want to build up odds that to phyla solved
#a problem exactly the same way? Ever look into an octapus eye lately?
#
Why is it a sore point? Two different species finding the same type of
device (an eye) was useful does not seem like a sore point to me. Why
do you find sore about it. I won't even mention the point that the eye
of an octapus is better than ours.
-Greg Hennessy, University of Virginia
USPS Mail: Astronomy Department, Charlottesville, VA 22903-2475 USA
Internet: gsh7w@virginia.edu
UUCP: ...!uunet!virginia!gsh7wchris@mimsy.UUCP (Chris Torek) (04/10/89)
>In article <3566@aplcomm.jhuapl.edu> jwm@aplvax.jhuapl.edu.UUCP (Jim Meritt) >writes: >>I don't think I am mincing words. (Neither do I; but then, I do this sort of thing often :-) ) >In article <28379@apple.Apple.COM> sabol@Apple.COM (Bryan Sabol) writes: >... Mutations are much more commonly deleterious than advantageous. True (or rather, `we believe this to be the case'). >... It is true that "a trait that is not selected against continues", >but neither does it change. Without the advantageous mutations, the >population/species would never change .... Except possibly to cease to exist. >[no] new species would develop at all.... So, if you really wanted to >be specific about how you phrase the process, it would be more accurate >to say that the filter that "does the selection" removes the deleterious >mutations, but the manner (at least for this arguement) in which new >species develop would be from advantageous mutations. Yes; >Therefore, one should say "why does ___ have ___", and not >"why doesn't ___ have ___". no. Actually, the question should then be `how might group G have acquired property P, and why might G-with-P be all that have survived to this day'---in this case, how did proto-birds acquire beaks (what sort of progression from teeth to beaks seems likely) and why did the beakless, toothy proto-birds disappear? -- In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163) Domain: chris@mimsy.umd.edu Path: uunet!mimsy!chris
sabol@Apple.COM (Bryan Sabol) (04/11/89)
In article <16816@mimsy.UUCP> chris@mimsy.UUCP (Chris Torek) writes: >In article <3566@aplcomm.jhuapl.edu> jwm@aplvax.jhuapl.edu.UUCP (Jim Meritt) >Actually, the question should then be `how might group G have acquired >property P, and why might G-with-P be all that have survived to this >day'---in this case, how did proto-birds acquire beaks (what sort of >progression from teeth to beaks seems likely) and why did the beakless, >toothy proto-birds disappear? Quite. (!) Wish I'd been able to say that. :-b bryan sabol ousted reedie-at-large.
dsr@uvacs.cs.Virginia.EDU (Dana S. Richards) (04/12/89)
In article <28379@apple.Apple.COM> sabol@Apple.COM (Bryan Sabol) writes: >In article <3561@aplcomm.jhuapl.edu> jwm@aplvax.jhuapl.edu.UUCP (Jim Meritt) writes: <<I believe "Why does __________ have _________?" is a creationists issue. <<It is implying design FOR something. < < "Creationist's"? Oh, PLEASE! Let's not start that! < <<The selection process, as I understand it, does not go FOR something but <<removes things that are less optimal for the immediate surroundings than <<other existant forms (unless that particular form is non-viable all on its <<own). The evolutionists question would be "Why does ________ not have <<_______?". This would be a search for why that feature was NOT selected. < < I think you're really mincing words here: ... < Now, I could argue that the giraffes of today's time have long <necks due to intraspecies competition for leaves on trees: the <longer-necked ones could eat more leaves. This is a "Why does ______ have <_______" statement. < Or, I could say that giraffes don't have short necks due to the <intraspecies competition for leaves on tress: the shorter-necked ones <had to eat the leaves lower-down on the trees, where all the individuals <could eat. This is a "Why does _______ not have _______?" statement. < < The two statements are equally valid; they're just looking at <the same evolutionary process from a positive-attribute and <negative-attribute standpoint, respectively. i think you may have missed the point. to someone who understands what is going on the two are interchangeable; in fact the positive-attribute approach is the most common because it seems to be the simplest and most direct version. unfortunately, if you do not know what is going on then the positive version is very easy to misinterpret as implying a directedness to the process. therefore i agree the negative version should be used more often to force your audience to realize they are equivalent (not rival) statements. dana
dan@acates.UUCP (Dan Ford) (04/13/89)
It seems to me that not all evolution can be explained in terms of simple environmental selection. My example is the albino cave fish, shrimp, and various varied darkness dwellers. These critters ware decendants from colored animals, and yet that have become albino. This cannot be due to environmental selection, since you cannot have selection for (lack of) color in the black caves. It is a repeatedly seen pattern of change, and not a single odd species mutation. What might be going on: In the above-ground population there is a constant (but small) mutation rate of albinos. On the surface this is very bad, and is quickly selected against. Underground, however, it is not a disadvantage and may continue in the gene pool. But, not only does it continue, but it apparently is selected FOR since you end up with all these albino animals. How can coloring possibly be selected for in a dark environment? Why a repeated selection of albino in an environment where color is meaningless? Odd theory, which I call evolutionaly entropy: complex structures must be selected for in order to continue, or they suffer from random mutation and are degraded, possibly disappearing from the gene pool. This is not to say that such things are selected against, but just that lack of selection FOR them is enough to have the trait leave. Complexity is good only if it solves a problem and improves surviveability, otherwise "keep-it-simple-stupid" (KISS). In this case, get rid of color since it isn't useful. Dan Ford uunet!acates!dan "You may not have stolen any eggs, but I bet you've poached a few." Odd Bodkins
mkkuhner@codon1.berkeley.edu (Mary K. Kuhner;335 Mulford) (04/14/89)
In article <273@acates.UUCP> dan@acates.UUCP (Dan Ford) writes: [Discussing albino cave animals] >Odd theory, which I call evolutionaly entropy: complex structures must be >selected for in order to continue, or they suffer from random mutation >and are degraded, possibly disappearing from the gene pool. This is not >to say that such things are selected against, but just that lack of selection >FOR them is enough to have the trait leave. Complexity is good only if it >solves a problem and improves survivability, otherwise "keep-it-simple-stupid" >(KISS). In this case, get rid of color since it isn't useful. >Dan Ford uunet!acates!dan Alternatively, there may be an actual cost to the animal of synthesizing melanin and other pigments, which could have a mild selective importance-- perhaps a pigment-producing animal must devote slightly more of its food intake to biosynthesis and has less to devote to reproduction. Maybe this could be settled with studies of comparative energetics, but it would be tough. Mary Kuhner mkkuhner@enzyme.berkeley.edu
ogil@tank.uchicago.edu (Brian W. Ogilvie) (04/14/89)
In article <273@acates.UUCP> dan@acates.UUCP (Dan Ford) writes: >What might be going on: In the above-ground population there is a constant >(but small) mutation rate of albinos. On the surface this is very bad, and >is quickly selected against. Underground, however, it is not a disadvantage >and may continue in the gene pool. But, not only does it continue, but it >apparently is selected FOR since you end up with all these albino animals. >How can coloring possibly be selected for in a dark environment? Why a >repeated selection of albino in an environment where color is meaningless? The situation could arise from mutation pressure without selection. The biochemical pathway involved in producing color (skin color, hair color, chitin color, etc.) is likely to be very complicated. If, say, twenty genes are involved in producing skin color (this is roughly the number involved in guinea pigs, I think), then a mutation in any one of these genes resulting in a nonfunctional protein would produce albinism (or a noticeable paling, or some other effect). Since a mutation from functional to non- functional is more likely than the other way, the net effect of unselected mutation would be partial to complete albinism. Assuming that the production of pigments takes some amount of energy (a quite reasonable assumption), then selection would be active in a dark environment, since those mutations which prevented the pigmentation system from operating would conserve the organism's energy. Such mutations would probably occur in the operator or promoter regions of the various genes involved, although large deletions would also reduce the energy devoted to pigment production. It would be interesting to compare the pigmentation systems of cave-dwellers and closely related surface-dwellers, though I'm not certain that it would be worth the genetic work involved. -- Brian W. Ogilvie / ogil@tank.uchicago.edu "Cartesianism is the most popular 'popular science' ever invented." --Noel Swerdlow
hjsdvm@ziebmef.uucp (Howard J. Scrimgeour) (04/23/89)
With regard to the development of albinism in cave animals, it is not necessary
to invoke a hypothetical entropy factor to account for this. Remember that
colour in an animal's skin is due to the presence of a pigment, such as
melanin. The melanins are large, complex molecules, and they cost the
animal energy to produce. In an environment where they are of no use,
the mutant which does not produce them gains an advantage.
..H. J. Scrimgeour, D.V.M.