Giraffe Evolution

[NavajoEverclear]

Surely this has been mentioned somewhere before, but i'll bring it up again.

 

Giraffes evolved longer necks because ones with mutations for longer necks survived better. But evolution is gradual so here is my question --- why did slightly longer necks help them survive? It might help to know the heights and populations of different types of trees that have grown in Africa, but assuming most are a certain height, only reachable by a longnecked girafe: why would slight increase make a difference? If one giraffe is two inches, or two feet taller than most others, but it still is not tall enough to reach the leaves, what is driving its evolution to be able reach it someday?

 

My guess would be that there is another gene or something that is related to neck length that is effected by other factors - maybe naturally more healthy, maybe sexual factors: long necks can kick other males butts (anyone know anything about girafe mating behavior?)? Long necks have sexier pheremones?

 

What do you guys think (or KNOW would be even better)?

[iglak]

perhaps the trees were not the same hight when that portion of evolution was taking place. if trees were lower, or if trees had leaves spread over the whole hight of the tree, then competiotion would be fierce for low leaves, especially when other animals are included.

 

the likely situation is that while giraffes evolved to eat high leaves, other animals evolved to grase and eat bushes. also, probably at the same time, the low trees were dying out because they were the easiest food, so evolution would make them taller where only the giraffes could reach.

[Cookie]

Well, early on, giraffes with slightly longer necks probably had no real advantage over giraffes with regular necks. But they had no disadvantage either, so the gene survived, continued to evolve, and eventually giraffes evolved that had a significantly longer neck -- at which point they had the advantage of being able to eat higher leaves. Giraffes with short necks then become disadvantaged, and are eventually bred out of the gene pool, leaving on long-necked giraffes.

 

Cookie

[iglak]

that could work, but why would longer necks evole away from short necks? if there was no evolutionery advantage, then they would interbreed and likely not change neck lengths by much.

[iglak]

of course, it's also always possible that there was a mutation that mass produced growth protiens and horomones, so that it was a giant leap (that could not be very giant in genetic terms) from short to tall.

 

<edit>

scratch that, it would be physically impossible for them to mate with the shorter ones.

[Cookie]

Well, it's like short and tall people. There's no great fitness advantage to being tall, and tallness runs in certain families, but that doesn't mean short people have been bred out of the population.

 

The advantage of having a long neck is only conferred once ther's a significant advantage to being able to eat taller leaves - this was probably a very graduaol response - talking time scales of tens of hundreds of generations.

 

Cookie

[iglak]

but that would create a very wide range of hights in giraffes, to the point that it would be physically impossible to mate with the shorter ones simply because they cannot reach. they could gradually evolve taller, but there couldn't be such a huge range within one species.

 

the only reason we have tall people and short people is because at one point in time it WAS an advantage to be taller... or shorter. those mutations did not gradually happen without being selected becaus ethey would have interbred and stayed relatively the same hight. we are interbreeding now and staying relatively the same hight, but we only started interbreeding after the hight variations were selected, which caused there to be such a big gap.

[Sayonara]

It's to do with resource partitioning and genetic fitness.

 

Look at the way there's nothing reach-wise between the 'regular' ungulates and what have you, and the giraffes & elephants.

 

And look at the way most of the chewy green goodness in their habitat is either close to the ground (low growth cost) or high in the air (reduced predation).

 

The rest should just fall in to place. I'd explain it better if I weren't tired and a bit drunk.

[mossoi]

I think that might be an idea because I can't really work out what you're saying there Saya

 

The giraffes with slightly longer necks will be able to reach slightly higher leaves and will do better at times when food is scarce. If the population is hit by a particularly bad drought for example the longer necks will be more likely to survive.

 

The other advantage of having a longer neck is the ability to see further, or over objects that you might be feeding on, even an inch in height may be just enough to avoid getting eaten by a hungry lion more often that the sucker with the short neck.

[iglak]

but the question is why did they get the long necks and tall bodies in the first place, not why it's good now.

[mossoi]

Through incremental changes as a result of evolution. The tall giraffe I'm referring to above is not as tall as today's giraffe but is just taller than the average allowing to outlive the shorter giraffes until there is another mutation where giraffes get taller again.

[YT2095]

their hearts had to adapt too, DID YOU KNOW.... (i learned this as a kid in school), that a giraffe has to bend it`s legs to get a drink of water because if it didn`t, the blood pressure to the brain would kill it!?

 

quite true, probably a little off topic, but I thought I`de share that when you consider that it`s heart had to evolve as well as it`s legs and neck

 

 

My 2 cents worth

[Cap'n Refsmmat]

Weird! That would be interesting to see!

[iglak]

wow! i did not know that. that's interesting.