What is the evolutionairy theory on the Giraffe?

The way evolution works is to offer up random mutations to non random natural selection.This means that ANYTHING that would increase the survival of an individual, would mean a greater chance of surviving to mate & therefore pass on those genes.In the case of a Giraffe, lets assume three scenarios ;1/ A light drought. The young Giraffes would be able to survive on their mothers milk whilst the mother was able to obtain both food & water. If food is plentiful enough, & leaves remain on lower branches, then there’s no particular natural selection going on here. The shorter necked individuals get as much food as the longer necked examples. All the young Giraffes are amply fed by their mothers milk.2/ A medium drought. The longer necked examples are able to get the upper leaves when the lower leaves are gone. They are still able to produce milk for their offspring, who survive. The shorter necked examples can’t get adequate food for both themselves & their young, their milk dries up & the young die. However, they, along with weaned adolescents are able to feed themselves. There is adequate lower level foliage.In this scenario, although the short necked adults survived, their young did not. As a result ALL surviving young had the long necked gene. As a result, there is a greater percentage of individuals with the long necked gene at the end of the year.3/ A hard drought. No Giraffes are able to sustain milk for their young & all young die. The short necked Giraffes aren’t able to feed themselves either, & die, along with the adolescents. Only the long necked adults survive, by virtue of their long necks & greater ability to feed themselves. This year has been a waste as far as offspring goes, but next year sees a reduced population entirely armed with the magic survival gene long neck. All offspring from now on will have the gene & what began as a mutation in an individual, has now entered the general population.------------------
Occam's razor is not for shaving with.

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Originally posted by redstang281:
So you are saying that the environment presents a need that must be forfilled in order for a species to survive? Which would mean in this case the environment presented the giraffe with vegetation above his head and the giraffe had to develop a longer neck to reach the vegetation or else it would die out?

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Sorry redstang, not sure if this was aimed at me or Joz. But anyway.....No. The environment is able to throw all sorts of things at the Giraffe, famine & drought among them. ANYTHING that gives a survival advantage to an individual will allow that individual to compete better for food, mates etc & pass those traits on. If the're good enough, they'll become the norm, given enough generations.I see what you're getting at re. HAVING to get long necks or die. If they couldn't get access to as much food as they do, then they would either be unsuitable for the habitat that they live in & become extinct there, or live where there is less competition for food. The fact it has a long neck, ALLOWS it to exist in habitats of drought & famine, enhancing the geographical diversity of that species, thus contributing directly to the success of that species.The question then arises, what happens to species like antelopes that don't have long necks. Surely they would die too? No. They have adaptions to the environment unique to themselves (incidentally there are species of long necked antelope, though not approaching that of Giraffes). this could be a different diet, a migratory habit etc.Incidentally, in the examples I gave, I tried to show how natural selection would work when a long neck was compared to purely a food variable. It also has the advantage of spying predators from far enough away that they don't become a threat. Thus "long necked" young are more likely to survive even when food is plentiful. Its entirely possible that the driving environmental factor behind long-neckedness was predator evasion. & that as a side advantage, they were able to get to higher branches.------------------
Occam's razor is not for shaving with.

"I must commend you on how well your informantion has been thought out."I thank you for the compliment Now, at the risk of repeating Mister Pambolis valid comments, I'll try to answer as comprehensively as possible.For evolution to work, every stage must have a survival advantage over the previous stage.
Given the similar starting points of proto-Giraffes & Proto-Antelopes, the similar ecological niches they occupied, similar diets, vulnerability to predators, heat, cold, drought, famine, disease, etc. At first glance its surprising they ended up with different adaptations.However, consider that all common ancestors of Giraffe & Impala ( I shall use Impala as my antelope example, as Impala & Giraffes occupy the same territory) were grass eaters. In times of drought this would result in colossal competition for grazing in times of drought/famine. An obvious advantage would be had by a species that branched out into non-grass foliage, shrubs, bushes, & trees etc. It is then no longer in competition for grazing area. That’s not to say drought is easy, but EASIER. A survival advantage has been gained. So now we have two types of savannah herbivore. Grass grazers (proto-Impala), & leaf eaters (proto-Giraffe).1/ Proto-Giraffes primarily eat foliage, so adaptations that give them more food will now/still be favoured. Foliage on the wooded savannah that they live exists as bushes & trees. So adaptations that give them greater reach to foliage that other animals can’t reach, i.e. the longer neck scenario described in my 1st post. Interestingly, the Giraffe could potentially have taken a different evolutionary route & widened its diet to eating grass (gone back to grazing). This would have at first glance, given it more food as well. However, it would have placed it back in direct competition with other grazers. Also, the predation factor could possibly have entered the equation here. That’s to say, animals with longer necks are safer from predation, particularly if this gives you a view over bushes if you frequent the woody part of the savannah. So, having longer necks & being safer from predation, also gives them the advantage of eating higher foliage. These two factors reinforce themselves. Higher neck = safer + more food. The longer the neck, the harder it is to graze on grass, so the less likely it would be to evolve back in that direction. It would mean a shorter neck, which would leave it more vulnerable to predation. As I stated earlier, for evolution to work, every stage must have a survival advantage over the previous stage. This would be a backward, less safe step, so didn’t happen. Or in the very least, examples that did were at a survival disadvantage & never survived .So, in the end it is has become a leaf eating specialist, possessing adaptations to keep look out for their young.2/ Proto-Impala are primarily grazers. It can & will eat foliage, but that’s not its modus operandi. Why? Being a grass eater, it preferred the more open savannah where it could see predators from a distance. On the open plain, a long neck & being tall, at first glance offers seemingly obvious advantages. However, the longer your neck, the further you are from your food (have you seen a giraffe drink?), so a grass eater with a long neck (beyond a certain point) brings more disadvantages than advantages, optimally speaking. So, what has evolution done to the Impala to ensure its survival? If it can’t have a long neck, it can be fast, & nimble. The evolutionary mechanism for this is fairly straightforward. Slow Impala are cat food & don’t live to breed. Fast ones do, & pass on fast gene. Another behavioural adaption is herding. Giraffes do live in small groups, but with long necks, this is less important. Impala live in larger herds, so there’s always a pair of eyes looking for predators. On the open savannah, this is crucial. Even in long grass the big cats have to work hard to catch Impala out.
So, in the end it has become a grazing specialist, protecting itself & its young with herding behaviour. If warned early enough, can get its young to safety.Once evolutionary paths have been undertaken they tend to reinforce themselves. I.e. Once longer necked proto-Giraffes appeared, going back to a shorter neck contained a survival diadvantage. Similarly, for the Impala to become slower & start solitary lives contains a disadvantage.As a result, Giraffes & Impala occupy different ecological niches & are, by & large not in competition with each other.The Giraffe has also become such a specialist, it has a prehensile tongue not suited to grass & its teeth also differ from the Impala. It has now limited itself to arboreal foliage. Even if it did have the dentition to eat grass, it doesn’t have the bone structure to graze on the floor easily. It is incredibly ungainly. It IS vulnerable when drinking but doesn’t have to do this often. Herbivores spend a large amount of time eating & can’t afford to be as vulnerable as the Giraffe is whilst drinking for too long.The obvious question is why didn’t the Giraffe evolve to eat both arboreal foliage & grass. The answer is perhaps that an adaptation that makes you good at something will make you less good at something else. In short, the compromises the Giraffe would need to make to eat grass & tree top goodies simply wouldn’t be worth it. It’s better off as a specialist, & those backward evolutionary steps to make it shorter again involve survival disadvantages. Or, that once the evolutionary path of leaf eater was taken, the going back was barred by increased competition. Why eat grass that isn't there because of drought, but there are tree top leaves that no-one else can reach ? The boon that was granted by lower competition arboreal leaf eating existence outweighed the high competition grazing compromise. That’s not to say Giraffe individuals were never born with shorter necks, somewhere along the line, just that there was survival advantage going one way not the other. i.e They died before they could breed.Evolution is not far sighted, it can only deal with what happens to a species, not what might happen.------------------
Occam's razor is not for shaving with.

No, I may have mislead you. The short neck gene is a gene that gives a slightly shorter neck than exists at the moment. Same with the long neck gene. There aren't two types of Giraffe born. One with a much longer neck than the other, the variations are small, & generationally cumulative, whether longer or shorter.In truth, there’s probably no such thing as either, its just a useful tool to explain the effects of a number of genes, leading to long & short necks, conveniently labelled long & short gene. But the effect & mechanism for transmission are the same.As far as mutation goes, there is an equal chance of mutation/sexual variation causing longer OR shorter necks in any one individual. It’s just that the environment will select for the one that gives the greatest chance of survival, the other will die out. Once again, its possible that a shorter necked individual gets lucky & finds all it needs to breed. But average weight of selection moves in favour of the genetic survival advantage.In short, the Giraffe will still have young with (slightly) longer & shorter necks. It’s just that only one will be generally selected by the environment to survive.Again, it’s possible that the weight of a longer (than they have now) neck now carries a disadvantage, given that no more food can be had, & the biomass of the extra length will require more food to metabolise. So EVEN LONGER necked individuals are selected against as well. The result is a roughly constant optimal length neck.Conversely, in times of plenty, shorter necked giraffes are still able to, by mutation/sexual variation have longer necked siblings as well as shorter ones. The same applies, the GENERAL movement is towards the greatest advantage. Longer necks."This would mean the short neck giraffe's would have to die out of starvation from loss of leaves on a lower vegation level. But how could a period of time like this exist if other lower animals with the same diet as the giraffe were able to survive?"Were talking about a habitat that spans many thousands of square km, & conditions will vary from part to part. So in an area of that habitat, where there IS drought, where it comes down to the last leaf, then the animal that gets it survives & all others become extinct. However, there are areas that will not be affected to the same extent by the drought. Therefore, it’s not to say that will necessarily cause extinction in an animal, just reduce population overall. Assuming the drought affected areas had survivors, the surviving population, taken as a whole, will have a higher incidence of the selected genes. However, natural selection of the Giraffes continues in these conditions. Even if all individuals die in drought affected areas, there is still the non/less-affected population elsewhere.However, not all leaf eating herbivores exist in exactly the same habitat as the Giraffe, many have ranges that overlap that of the Giraffe, & exist in areas where they don’t compete with it. So extinction of an organism in a Giraffe area still allows recolonisation. Alternatively/additionally they may have adaptation that make them less vulnerable to famine. For example migratory ability, more variable diets, etc.To point out the obvious ; If there was a foliage eater that was less adapted to its diet than the Giraffe & had the same geographical range or less, & also possessed no other adaptations to its habitat, then the Giraffe out-competed it long ago, & no such organism is alive today.------------------
Occam's razor is not for shaving with.

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[This message has been edited by mark24, 12-15-2001]

Give me all the Okapi info you have & I'll be happy to give it a bash.....

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Originally posted by redstang281:
So in order for the okapi and giraffe to evolve then they must have been geographically seperated?

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The okapi is alive today. He is a foliage eater - the same diet as the giraffe. He is infact a close relative to the giraffe. This shows that he was able to survive without evolving a longer neck.

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As Percy states, its not a requirement. It would depend on levels of competition. This allows for more than one organism occupying the same ecological niche.Okapi are rainforest dwellers & Giraffe live on woody savannah. So they are geographically separated.A VERY long neck in a rainforest isn't a survival advantage.If the Okapi & Giraffe are related, doesn't this imply common descent?------------------
Occam's razor is not for shaving with.

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[This message has been edited by mark24, 12-16-2001]

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Originally posted by redstang281:
Why?

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As I asked earlier, is it possible that the giraffe's long neck helps the environment in anyway, or no?

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1/ If a Giraffe was in a rainforest, its head would constantly be in the interlocking tree canopy. Simply moving is a problem. Restricted view for predator evasion, not to mention flight.2/ Yes & no, depending on whether your a tree, having your seeds dispersed in Giraffe dung, or an insect sitting on a high leaf about to be eaten.------------------
Occam's razor is not for shaving with.

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Originally posted by redstang281:
Which would help to keep insects from becoming over populated.

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Why did just the giraffe's neck grow and not his whole body? Why did he become misproportioned?

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Not sure of your point as regards insects.The Giraffes neck grew more than its entire body as this is the most economical way of gaining height. A huge body requires more food than just a long neck. For the Giraffe, a huge body & the extra bones & musculature required to support it is a survival disadvantage compared to a long neck. ie It may cost more to keep than the extra food it brings in.The Giraffe isn't misproportioned, it is OPTIMALLY proportioned for its lifestyle.------------------
Occam's razor is not for shaving with.

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[This message has been edited by mark24, 12-16-2001]

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[This message has been edited by mark24, 12-16-2001]

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Originally posted by Percipient:

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Mark24 writes:
The Giraffe isn't misproportioned, it is OPTIMALLY proportioned for its lifestyle.

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An interesting question often asked about ID (which I know isn't advocated by Redstang, I introduce it for another reason) is why God's designs are identical with evolution. This often comes up when people question why God would design humans so poorly, eg, why the appendix, why blood vessels in front of the retina, why a body cavity design best suited for horizontal positioning, why tonsils, and so forth. The argument is that good enough designs, vestigial organs, etc, are what one would expect of evolution, not of a divine designer.

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Assuming consistent arguments are preferable, could it instead be argued that the giraffe body design is good enough for its ecological niche, rather than optimal?

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--Percy

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I concede the point.I was just trying to get across the point (badly) that a Giraffe can only be misproportioned when compared to another Giraffe, at least thats what I was trying to say!!Evolution would be well described as "the search for the optimal design".While I'm at it, my answers to Redstang are not meant to be absolute truths, just possible/likely scenarios that describe how mutation & natural selection combine to allow variation not allowed by purely sexual (or asexual, for that matter) reproduction.------------------
Occam's razor is not for shaving with.

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[This message has been edited by Percipient, 12-17-2001]

[QUOTE]Originally posted by redstang281:The creationist pov of vestigial organs is that we just don't know what they do yet.[/B][/QUOTE]Wouldn't you be able to determine this by looking at an organism that had the fully developed organ? eg Ruminants. In the case of the caecum (appendix)its for digestion of cellulose. All the other organs in ruminants have the same function as our organs, liver, kidney, lungs. Our caecums produce no hormones or enzymes, & no longer digest cellulose, or anything else for that matter.The organ IS function-less.If the caecum has a function, the onus is on creationists to show it, where science has failed. Go on, theorise.------------------
Occam's razor is not for shaving with.

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Originally posted by redstang281:
Did you know that a full grown giraffe's heart weighs over 24 pounds and pumps 16 gallons a minute? Because the giraffe's heart is much larger than his head, a series of special one-way, back-flow preventer valves are needed in the neck to regulate the flow of blood to the head, especially when the giraffe is bending down to get that much needed drink of water. Without these valves, the immense blood pressure coupled with gravity would make for one nasty headache and other such repercussions. Elastic blood vessels in the giraffe's head allow harboring of enough blood to prevent the giraffe from passing out when bent in this position.

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How did this evolve?

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A mutation that placed pre-existing venal valve in arteries? Veins/capilleries are elastic anyway, so successive mutations that make the said vessels "more elastic" would do the trick.------------------
Occam's razor is not for shaving with.

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Originally posted by redstang281:
Wow, so not only would all that have to occur, but also the giraffe would have to be isolated and we would hope that the giraffe baby could nurse milk off the giraffe for a long enough time to grow to reach the tree branches.

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I answered infant Giraffe survival in my first post.

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Originally posted by redstang281:
This is why the evolution community has given up on that theory of giraffe evolution and has started a new one.

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Science has the ability to adapt to new evidence as it becomes available. If the same were true of you you wouldn't be trotting out "Mutations are never "good" or helpful to an organism. The plant or animal that is mutated is always worse off than he was before." 60 years after it ceased to be an issue.

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Originally posted by redstang281:
Meanwhile the creationists still maintain the giraffe was created a giraffe as God designed him as one of the creatures to help maintain plant grow.

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Fine, I only require you to prove it.------------------
Occam's razor is not for shaving with.

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Originally posted by Fred Williams:
I've been watching this thread with interest.

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Question to evolutionists: If the giraffe's neck would have required many random mutations without the advantage of selection, do you agree this would make the evolution of the giraffe's neck highly implausible?

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Gotta run. I should be back sometime tomorrow.

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Actually a good question, my first answer would be yes, it would be implausable. However,"If a population is finite in size (as all populations are) and if a given pair of parents have only a small number of offspring, then even in the absence of all selective forces, the frequency of a gene will not be exactly reproduced in the next generation because of sampling error. If in a population of 1000 individuals the frequency of "a" is 0.5 in one generation, then it may by chance be 0.493 or 0.0505 in the next generation because of the chance production of a few more or less progeny of each genotype. In the second generation, there is another sampling error based on the new gene frequency, so the frequency of "a" may go from 0.0505 to 0.501 or back to 0.498. This process of random fluctuation continues generation after generation, with no force pushing the frequency back to its initial state because the population has no "genetic memory" of its state many generations ago. Each generation is an independent event. The final result of this random change in allele frequency is that the population eventually drifts to p=1 or p=0. After this point, no further change is possible; the population has become homozygous. A different population, isolated from the first, also undergoes this random genetic drift, but it may become homozygous for allele "A", whereas the first population has become homozygous for allele "a". As time goes on, isolated populations diverge from each other, each losing heterozygosity. The variation originally present within populations now appears as variation between populations." (Suzuki, D.T., Griffiths, A.J.F., Miller, J.H. and Lewontin, R.C. in An Introduction to Genetic Analysis 4th ed. W.H. Freeman 1989 p.704)What this means is gene A in a (small)population that are randomly (sexually) selected, by chance have a greater percentage expression in the population as a whole, compared to gene B. This is entirely feasable, just random (If you replayed the scenario, gene B would be just as likely to be slightly dominant). However, in generation 2, because gene A was more numerous, the random sexual expression could go slightly either way. But because there are more gene A's in the population the likelyhood is that the incidence of gene A will increase further, until the population is homozygous with gene A (man, i need a dictionary).This genetic drift is new to me, & I can immediately think of a few problems, so I need to read up on this a bit more before before I become convinced.It's a bit off topic but I'll give you the adress anyway http://www.talkorigins.org/faqs/genetic-drift.html There's probably nothing disagree on, either, just for info.------------------
Occam's razor is not for shaving with.

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[This message has been edited by mark24, 12-18-2001]

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Originally posted by Fred Williams:
Well, here is the dilemma you face. Did you know that a full grown giraffe's heart weighs over 24 pounds and pumps 16 gallons a minute? Because the giraffe's heart is much larger than his head, a series of special one-way, back-flow preventer valves are needed in the neck to regulate the flow of blood to the head, especially when the giraffe is bending down to get that much needed drink of water. Without these valves, the immense blood pressure coupled with gravity would make for one nasty headache and other such repercussions. Elastic blood vessels in the giraffe's head allow harboring of enough blood to prevent the giraffe from passing out when bent in this position.

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Now, how do you propose these valves evolved? Natural selection cannot help because the valves are useless until functional. So you need a bunch of lucky mutations for this scenario to play out. The odds of this happening by pure chance is pretty much impossible. You admitted above that without selection, its an implausible scnario. Its time to listen to yourself, let go of your fairytale, and come to your senses.

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(If you would like to see what happens to the poor Giraffe, go here: http://www.evolutionfairytale.com/giraffe1.htm)

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BTW, genetic drift is a problem for evolution. Many evolutionists realize this and reject the small population model of upward evolution. Why? Because if selection is rendered powerless, deleterious mutations will surely outpace beneficial ones since there are so many more of them.

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Firstly, a valve is anything that can restricts flow in one or both directions. A small flap which bends one way & less so in another would have the ability to restrict flow in one direction. This is true REGARDLESS OF HOW SMALL it is. If it proved to be an advantage then nat. sel. takes over.Lucky mutations, yup. But then Ive got a lot to choose from.Genetic drift does not render natural selection powerless, it operates along side it. So, I doubt if "many evolutionists" do reject drift for that reason.I did admit the scenario would be implausable without natural selection, but then I never said it did it without it.------------------
Occam's razor is not for shaving with.

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Originally posted by Fred Williams:
I realize you are trying to invoke homeobox mutation. It’s a nice try, but it won’t cut it. For one, the pressure gradients would be dissimilar. If you are familiar with fluid mechanics, the pressure required to pump something upward increases an amount that is more than proportional to the increase in height. Ie it’s logarithmic. You can’t expect the correct pressure valve to just pop into place. Another problem is the fact that there exists a labyrinth of these valves in the Giraffe’s neck. There is no way to conceive of all these valves being recognized independently by selection, which is what you are implying. I’m trying to determine how much luck is needed. How many mutations are you willing to grant that are not going to be recognized by selection? You know you are grasping at straws when you try to say one.

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Nobody saying that the Giraffe had a long neck, THEN it got valves. As the Giraffes neck lengthened, the valves were selected for by ns. based on fitness of mutation. As both I & percy have alluded the valves pre- existed. What was required was a mutation leading to developement of those valves in arteries & not just veins. Those valves clearly would't work for a modern Giraffe, but then no ones saying they appeared in a modern Giraffe. Venal valves in arteries would be better than no valves at all in a proto Giraffe. Valves would evolve alongside the neck.How many mutations would you grant for a valve? Please give reasons including references to rm, ns , genetic drift, recombination, & lateral gene transfer.------------------
Occam's razor is not for shaving with.

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[This message has been edited by mark24, 12-21-2001]