I can't understand evolution occurring...

Question

Giraffes, or their ancestors, started of with small, normal necks. But then a mutation occurs, giving a giraffe a longer neck, meaning it can reach higher vegetation. But mutation occurs randomly, so the giraffe could have mutated an odd bump on its side, or could have developed a faulty ribosomes, but it just happened to evolve a long neck which was perfect for it?

Doesn't that seem unlikely, or have I got something wrong??

Also it is even more unlikely that this was the first external mutation that occured in a giraffe's ancestor, so why don't we find giraffe-like fossils with very unusual extremities?

PS. This question is from a very confused agnostic!

Answer 1

It didn't evolve randomly...it's survival of the fittest. The animals with advantageous characteristics will survive and reproduce, passing on their traits to their offspring, while the animals with disadvantageous characteristics will slowly die off. As for the other part of your question...I dunno, I don't study fossils. :)

Answer 2

It's not unlikely at all, and you totally have it right.

Unfortunate mutations like faulty ribosomes and bumps on the neck happen all the time.  But because they cause problems for the animal, the animal has less chance of living a long life, and therefore less chance of passing on the mutated genes.  This type of mutation could easily cause the animal to die shortly after birth, if it was a big enough problem.  Ask a farmer...they'll tell you that it's not uncommon at all for a newborn foal or calf to have a short leg or something that makes it impossible for them to walk to their food.  And animals don't generally nurse the 'faulty' newborns.  We've seen elephants in the wild do it, but for the most part, any animal that isn't in peak form is left behind to die on their own.

The beneficial mutations help the animal live longer, and help its offspring live longer.  Because the mutation helps them, they become the stronger version of the species, and eventually, all of the iterations that don't have that mutation are simply bred out of the gene pool.

The reason we haven't found giraffe-like fossils with very unusual extremities is that we haven't found very many giraffe-like fossils.  There aren't the same number of fossils out there as animals that were once living.  It's entirely possible that we will find on some day, really.

Does that answer your question?

Edit:

As I said above, mutations happen all the time.  It's simply a genetic accident - sometimes it's helpful, and sometimes it's not.  All of the incomprehensible number of potential mutations probably DID happen, but weren't bred back into the gene pool, in order to continue the development of the mutation.

It's very possible that there have been zebra mutations to make the zebra's neck longer.  The difference is that a longer neck didn't help the zebras, because they had access to food on the ground.  Because it wasn't needed, breeding continued with all of the other zebras with "regular" neck lengths, therefore the regular length neck continued in the gene pool.

As to your question of where the genes came from...They came from the giraffe's parents.  These were initially genes for a "regular" neck length, but somewhere in the process, something went wrong...it's just that this particular "wrong" thing happened to be helpful.

For example - we see kids born all the time, with Down's Syndrome.  These kids have all of the genes that their parents gave them naturally, but because of an error in the chromosomal development process, they are born with different physical characteristics than their siblings.  Down's Syndrome is one of those genetic accidents that is problematic, but the same concept applies to other genetic accidents that are helpful.  A mutation is nothing but a genetic accident.

Answer 3

The part you are missing is *VARIATION*.

It is NOT that a pre-giraffe suddenly evolves a "long-neck" mutation.

It is within the entire population of pre-giraffes there is a normal *variation* of neck lengths.  

If the creature lives in an environment or lifestyle where the ones with the slightly longer neck have a tiny advantage over the ones with the shorter necks ... then generation after generation the species will get slightly longer and longer necks ... just because the taller ones get to leave the most babies.

Why would a longer neck give a slight advantage?  It's not as simple as the shorter-neck giraffes completely unable to reach food ... it's that they are *competing* for food with the longer-necked giraffes that have a wider range of food to reach ... so the taller giraffes spend less time grazing and more time (ahem) making babies.    Sexual selection is also believed to play a part ... it is part of mating rituals, and competition between males for females, so the longer-neck giraffes get the most mating opportunities.

It also doesn't matter that females are shorter ... females aren't competing with males for reproductive rights.   The females with the longer necks outcompete the females with shorter necks ... and males with longer necks outcompete the shorter males

... and so the taller females will mate with the taller males ... and (you guessed it) the resulting offspring will have slightly slightly taller.   Again, year after year, generation after generation ... millions of years on millions of years.

The important point is that it is NOT a single mutation.

Answer 4

There are a variety of survival strategies.  Giraffes developed a survival strategy for which height was an advantage.  Using the innate variations in neck length among the original population, maximum neck length would be achieved in a few generations.  At this point, a new trait for slightly longer neck would create a substantial advantage, as the new trait gives an advantage to the offspring of that one giraffe.  It is not just the one mutation that occurs.  There could have been a mutation for a shorter neck, but that was a disadvantage, and results in fewer offspring until the trait is lost.

Zebras didn't compete by neck length, so variations in neck length will center around the length that is most advantageous (for example balancing speed and good position for foraging).  Although striped like a zebra, the best example of a "short-necked giraffe" would be the okapi.

Answer 5

Natural selection works so that the giraffes with sort of longer necks were the ones to get the food which means they were the most likely to survive, which means they were the ones to mate, slowly killing off the smaller necked ones.

Many many generations of this happening over time gives the result of all giraffes having long, efficient necks.