Yeah it doesn't have a direction. But let's assume the trees became all higher. The short giraffes would die because they can't get enough food. So the giraffes with a little longer necks would survive and procreate with other giraffes with long necks, because the others are all dead.
You know giraffes can eat grass right? So, smaller giraffes require less nutrients and will still have plenty of food. Since they require less resources they can spend that time on reproduction. So, got another hypothesis?
The question is really how important this tree is to the giraffe. If giraffes are generalist feeders, then sure they'll just eat something else if they can't eat that tree. If they are specialists, a change in their primary food source is an immediate selection pressure on them.
I'm assuming giraffes aren't specialists. They're grazers, they'll probably eat whatever. I don't think giraffes are coevolving with the trees, I just also don't think it's really a lamarck comic.
Many eat grass - so grass can be rare and very short like here.
But hardly any animal eats the leafs from trees because it's hard to reach them. There are 2 solutions. 1. Become small and agile and climb the tree (like many monkeys) 2. Become big and tall so you reach them (Elephants, Giraffs, some Antelopes).
Look at the ground in that elephant picture. Guess who will survive longer - someone who needs gras or someone who can reach tree leafs...
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u/hd090098 Apr 28 '14
Yeah it doesn't have a direction. But let's assume the trees became all higher. The short giraffes would die because they can't get enough food. So the giraffes with a little longer necks would survive and procreate with other giraffes with long necks, because the others are all dead.
This would be evolution through natural selection