Zoology

Why Giraffes have Long Necks



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"Why Giraffes have Long Necks"
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Giraffes are beautiful, unique animals that have come to an interesting solution to the problem of interspecies competition for food. It has long been one of the best examples to use to show the different theories of evolution.

It is important to understand a little natural history on giraffes and their way of life in order to be able to discuss how they may have come to this lifestyle. The giraffe is native to Africa and subspecies exists in many habitats within this region. Their range extends from Chad to South Africa, although it is not continuous. Giraffes feed on the leaves from the acacia trees primarily but will eat other foliage. They possess long prehensile tongues that are impervious to the thorns from these trees. Family groups consist of females and their offspring. Males are found either in bachelor groups or as solitary animals when they are older.

Many people word the statement of giraffe evolution in such a way that it sounds like the giraffe chose to have a long neck in order to be able to feed from acacia trees. This is a very Lamarkian way of thinking about this. Lamark's theory of evolutionary change states that children will inherit the traits of their parents. If baby giraffes were supposed to have longer necks because their parents had to stretch for the leaves, then wouldn't it be fair to assume that human babies born to body builders should be extremely muscular. We know this is not the case because traits that are acquired throughout an organism's life are not passed on genetically.

It is much more likely that giraffes started out as general browsers (eating leaves and bark off of foliage) and later developed a specialization for the acacia tree. The length of neck would have come to be randomly. For example, there may have been a calf born who had a neck that was on the long end of the normal range (all traits exist on a range that will form the natural shape of a bell curve). If the calf is female, she will hold the chance of passing this mutation on to her children. If the calf is male, he will also hold the chance of passing the mutation on to his offspring. If the initial calf was male, or if the first female managed to pass this mutation on to one or more of her male offspring, it would show up in a larger percentage of the population due to a male having many offspring within a single year. Females of most ungulates will only give birth to a single calf every year or two, depending on the species.

The biggest key to evolutionary thinking is "Why would that mutation be advantageous?" There are a couple reasons that would favour the longer necked early giraffes. The first would be that they could reach leaves that are higher up in the trees. If there was heavy competition for food resources, this would be advantageous over their shorter necked relatives because they would be able to reach food that other animals could not. In a hard year, many of the shorter necked variety many have died due to starvation. Evolution works not by being born into the population but by being able to have as many babies as you can in the next generation. The scientific definition of evolution is "the change in the percentage of genetically controlled traits from one generation to the next." Over time, competition may have continued to favour longer and longer necks among the giraffe's ancestors.

A second reason that longer necks may have helped some ancient giraffes survive better than others is predation. Being able to see over the heads of their peers may have given them earlier warning that danger was near. Most predators will pick off the easiest prey possible. They take the young, old, weak, and slow. If longer necked giraffes were able to have advanced warning and a head start over their peers, they would have been more likely to survive.

There are no other known species that have evolved a similar solution for the problem of interspecies competition for food. They are the first species to have achieved a long neck that is in an upright position and meant to help reach food that is located higher up.

As an interesting side point:
Many dinosaurs have been depicted in similar positions but this is not correct. The configuration of the vertebrae in the necks of these dinosaurs was not created to lift high off the ground. They would have stuck strait out in front with the tail sticking strait out the back to act as a counter balance. The tail would not have dragged on the ground.

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