Why does a giraffe have a long neck?

[JohnR7]

Ok, the theory is that a giraffe developed a long neck and long legs to reach the tender leaves on the top of the tree. Can someone give me a more exact description on how the neck and legs got longer? I need a little bit more than just a generic answer saying long necked giraffes were selected over short necked giraffes. I need to know why some giraffes had longer necks and why some had short necks. Also, how did longer necks get longer over time?

 

[Bushido216]

Hrm.

I'll take a simple shot at this because I'm bored.

Let's say that there are, for simplicities sake, two types of giraffes. Type A with shorter necks, and Type B with longer necks.

Obviously, B will have an advantage over A in gathering food from high branches. Because of this advantage B genotypes will be able to reproduce more, and therefore the representation of their genotypes will increase proportional to the representation of A genotypes.

Afterall, natural selection is about changing the relative frequencies of allelles in a population.

So, B has increased tremendously over A to the point where A is almost non-existant. Type C appears having a slightly longer neck that Type B. The process outlined above repeats itself. Any Type that had a shorter neck would have its allelles lost before it could get off the ground because of a serious fitness disadvantage.

 

[JohnR7]

Let's say that there are, for simplicities sake, two types of giraffes. Type A with shorter necks, and Type B with longer necks.

Yes, natural selection tells us that the giraffe with the longer neck is going to be selected. But natural selection does not tell us where the longer neck came from or why the selected giraffe has a longer neck in order to be selected. Unless there is some sort of variation that takes place.

Perhaps as the shorter necked giraffes are eliminated, the variation continues to kick in to create giraffes with longer and longer necks.

 

[Bushido216]

Essentially.

The variation is random. In each generation you're going to have multiple types of giraffes variating from the mean. As the mean shifts due to natural selection the variations shift along with it, if you gather. As in, you're less likely to get a giraffe with a 5' long neck as a 6' long neck if the mean is 7', and likewise with 8' and 9' long necks in the other direction.

 

[JohnR7]

Essentially. In each generation you're going to have multiple types of giraffes variating from the mean.

Ok, I will accept that, so even though you have created a new mean, the variation on that mean remains consistant. As long as you have the trait in the first place to select from. I am not so sure if that could explain how a fin could turn into a foot or a foot could turn into a fin.

 

[Bushido216]

Ok, I will accept that, so even though you have created a new mean, the variation on that mean remains consistant. As long as you have the trait in the first place to select from. I am not so sure if that could explain how a fin could turn into a foot or a foot could turn into a fin.

Don't take my word as gospel. The variation on the mean can be incredibly large. But the types of mutations you're going to get are going to be constrained by the genetics of the animal. I'd be very surprised if a giraffe mutated a fin because the genetics for a fin simply aren't there.

To go back to your foot to fin example it'd never happen. You have only the genetics of the parent organism to work with. However, large scale changes can happen as a result of the mean being shifted ever so slightly many, many, many times.

 

[JohnR7]

However, large scale changes can happen as a result of the mean being shifted ever so slightly many, many, many times.

As long as you have variation. Of course in the real world, you would most likely have coevolution. There most likely would be something that is causing the trees to get bigger and taller. Maybe the little trees are getting eaten up, so the selection would be for the bigger trees that provide more food for the giraffe.

 

[Bushido216]

Yes. Evolutionary biology in the actual world is far more complex than I could ever explain. The purpose of these examples is jus to demonstrate the mechanism. The interplay is hugely complex.

 

[Ondoher]

Ok, the theory is that a giraffe developed a long neck and long legs to reach the tender leaves on the top of the tree. Can someone give me a more exact description on how the neck and legs got longer? I need a little bit more than just a generic answer saying long necked giraffes were selected over short necked giraffes. I need to know why some giraffes had longer necks and why some had short necks. Also, how did longer necks get longer over time?

It is hard to understand the exact selection pressures that led to the origination of any specific species, although genetics can help at times.

I happen to be of the opinion that exagerated features like the peacock tail and the neck of the giraffe are the cause feedback loops typical of sexual selection.

Not sure if there is any research to support this, however.

 

[Bushido216]

Hm. I always forget sexual selection.

Unfortunately the narrowness of my education on the subject doesn't lend me towards being able to consider such forces.

 

[JohnR7]

Hm. I always forget sexual selection.

Are you suggesting that the women giraffes select the male giraffes with the bigger longer neck?

 

[WaZoO]

Are you suggesting that the women giraffes select the male giraffes with the bigger longer neck?

Innuendo?

I don't know if a longer neck would make much difference in sexual selection, why not just stick with the much more obvious mechanism that made their necks grow, ability to reach more food?

 

[Bushido216]

Actually Ondoher originally did. But it's possible.

The exact selection pressures for each adaptation is hard to know right off the bat. It requires alot of research for each organism and there are plenty of organisms. Perhaps long necks are both a sexual trigger and a practical one, like musculature in humans. A strong, muscular will be more able to reproduce BOTH because women find him attractive and he will be better able to survive (and thus have time for the hanky panky).

 

[Bushido216]

Innuendo?

I don't know if a longer neck would make much difference in sexual selection, why not just stick with the much more obvious mechanism that made their necks grow, ability to reach more food?

It's possible that it's both. For instance. A wrench is incredibly handy for applying leverage in hard to lever places. That is a wrench's intended purpose but that doesn't detract from its duality as a handy attention-getter.

 

[Ondoher]

Are you suggesting that the women giraffes select the male giraffes with the bigger longer neck?

It could be more subtle. I believe that giraffes spar for mates using their necks. A longer neck could assist with this effort. A bit like large antlers on deer.

 

[Ondoher]

Innuendo?

I don't know if a longer neck would make much difference in sexual selection, why not just stick with the much more obvious mechanism that made their necks grow, ability to reach more food?

In general, exaggerated features appear to be the hallmark of sexual selection, that's all.

 

[Aron-Ra]

Yes, natural selection tells us that the giraffe with the longer neck is going to be selected. But natural selection does not tell us where the longer neck came from or why the selected giraffe has a longer neck in order to be selected. Unless there is some sort of variation that takes place.

PubMed indicates that there are an average of 128 mutations per every human zygote, and that these mutations are the reason that two brothers who share both of the same parents won't look exactly alike; they're 256 mutations apart from each other. And while there is some return to the "main", (some inherited similarities tend to skip a generation) they will never return completely to the exat genetic composition of their grandparents. So there is a continual divergence. Usually, divergence from the established norm has no real selectable value, and will bred back out. This is one of the benefits of sexual selection. But when there is an incidental advantage that can be selected for, such as slightly longer vertebrae for the giraffes, then certain groups may, over time, expand on that, and the trait may even be built upon.

Perhaps as the shorter necked giraffes are eliminated, the variation continues to kick in to create giraffes with longer and longer necks.

In a sense, yes. But the ancestral stock is not always eliminated. And in the case of the giraffes, there are many in the fossil record that aren't around anymore. But there is still one species of short-necked giraffe.

Its called the okapi.

 

[And-U-Say]

Are you suggesting that the women giraffes select the male giraffes with the bigger longer neck?

Hey! Bigger is Better! Proof that size DOES matter.

 

[Tomk80]

If I recall correctly, reaching for food alone isn't enough to explain the long necks of giraffe and sexual selection does indeed come into it. As Ondoher pointed out correctly, the male giraffes spar by swinging their long necks against each other, sometimes with lethal results.
Now to find the pubmed article where I read all this.

 

[Mistermystery]

If I recall correctly, reaching for food alone isn't enough to explain the long necks of giraffe and sexual selection does indeed come into it. As Ondoher pointed out correctly, the male giraffes spar by swinging their long necks against each other, sometimes with lethal results.
Now to find the pubmed article where I read all this.

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