What is the evolutionairy theory on the Giraffe?

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But if they have a long neck that shouldn't limit them to only eating vegitation from the top. It should only give them a greater range to select from. A giraffe does have to drink water on the ground, so he is capable of lowering his neck. So if vegitation wasn't left at the top from other long neck animals eating it, then he could certainly eat near the middle or the bottom.

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This is indeed the point about environmental pressures. The giraffe can graze at ground level but is clearly not as well adapted to do so as, for example, antelope.If the loss of treetop fodder were sustained enough, the giraffes, which in the short term struggled by, would be out-competed long-term by the antelope who were far better able to graze there and would die out. Perhaps a lineage of shorter necked giraffes, better suited to grazing on the ground, would evolve. Perhaps not.You'll be interested to know, by the way, that giraffes bending down at waterholes are quite vulnerable to attack from predators so they often drink in pairs so one of them can act as a lookout. This is a nice example of how behaviour and physical traits can combine to address selective pressures.The plight of the red squirrel in Europe and the Douglas squirrel in the States is an example of the kind of grazing selection you discuss with regards to giraffe.The grey squirrel can outcompete both these species by a number of means - perhaps more intelligence, perhaps aggression, but also because they can eat nuts which are less ripe. As a result, there are fewer nuts left for other species. The red and Douglas squirrels, may evolve behaviourally and physiologically to compete, but at the moment they are losing out.BTW, nice thread, thanks.

"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.

In order for the giraffe to aquire his long neck the long neck gene would have to be passed down to the younger generations. Which would mean that the gene could only come from giraffe's who have longer necks. So therefor in order for all giraffe's to have longer necks there would have to be a period of time in which no short neck giraffe's could survive to pass along their shork neck gene's. 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?

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[This message has been edited by redstang281, 12-14-2001]

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]

Would the giraffe's evolving long neck have any positive side effects on the environment?

How did the animal the okapi evolve?

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Redstang writes:
How did the animal the okapi evolve?

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I would like to thank Mark for his very well thought out descriptions of possible evolutionary scenarios for the giraffe. If he wants to also tackle the okapi I think that would be great, but what your series of questions indicates to me is that you're seeking questions for which we do not have answers.If we find answers to all your questions it only means you're asking the wrong questions. The toilers in the field of science are pondering plenty of unsolved mysteries, and there are tons of questions for which we have no answers. What would it mean if you asked some of these questions, such as does Higg's Boson exist, or is string theory correct, or how did life originate? When we said we didn't know, do you believe it would then be valid to conclude this was evidence of the divine at work? If so, then welcome to the world of Intelligent Design.--Percy

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[This message has been edited by Percipient, 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 mark24:
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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.

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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. Thus the question remains why did the giraffe evole a long neck?

[QUOTE]Originally posted by Percipient:
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Redstang writes:
How did the animal the okapi evolve?[/QUOTE]

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I would like to thank Mark for his very well thought out descriptions of possible evolutionary scenarios for the giraffe. If he wants to also tackle the okapi I think that would be great, but what your series of questions indicates to me is that you're seeking questions for which we do not have answers.
[/B]

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He definatly did put a lot of thought into it. [b] [QUOTE] If we find answers to all your questions it only means you're asking the wrong questions. The toilers in the field of science are pondering plenty of unsolved mysteries, and there are tons of questions for which we have no answers. What would it mean if you asked some of these questions, such as does Higg's Boson exist, or is string theory correct, or how did life originate? When we said we didn't know, do you believe it would then be valid to conclude this was evidence of the divine at work? If so, then welcome to the world of Intelligent Design.
[/b][/QUOTE]Are my questions not welcomed?

You're questions are very welcome. I was just wondering where you were going with them. If not toward ID, then just forget I said anything.There is one more thing I'd like to add. This is not in any way a criticism of Mark's scenarios, just a clarification. The scenarios are only applications of the evolutionary framework to the available evidence and are not evidence themselves. One of the giraffe scenarios may be true, or perhaps it happened some other way. For instance, one possibility Mark doesn't mention when contrasting giraffe and impala development is that their common ancestor may have become separated into populations in different geographical regions before being reunited on the savannah of modern day Africa. And adding that scenario probably still doesn't cover all the bases, because in general in any field as study as you expand the details in the scenarios the necessity for subdividing them arises.--Percy

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Originally posted by Percipient:
You're questions are very welcome. I was just wondering where you were going with them. If not toward ID, then just forget I said anything.

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There is one more thing I'd like to add. This is not in any way a criticism of Mark's scenarios, just a clarification. The scenarios are only applications of the evolutionary framework to the available evidence and are not evidence themselves. One of the giraffe scenarios may be true, or perhaps it happened some other way. For instance, one possibility Mark doesn't mention when contrasting giraffe and impala development is that their common ancestor may have become separated into populations in different geographical regions before being reunited on the savannah of modern day Africa. And adding that scenario probably still doesn't cover all the bases, because in general in any field as study as you expand the details in the scenarios the necessity for subdividing them arises.

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--Percy

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So in order for the okapi and giraffe to evolve then they must have been geographically seperated?

It's not a requirement, but it is one of the possibilities.--Percy

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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 mark24:
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.

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Okapi are rainforest dwellers & Giraffe live on woody savannah. So they are geographically separated.

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A VERY long neck in a rainforest isn't a survival advantage.

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Why? [b] [QUOTE] If the Okapi & Giraffe are related, doesn't this imply common descent?
[/b][/QUOTE]I was speaking from an evolutionist pov.As I asked earlier, is it possible that the giraffe's long neck helps the environment in anyway, or no?