The Appendix

[simple]

I was speaking wtih a friend earlier about evolution and he was questioning it... I believe in evolution but I would just like a few things cleared. First off, I was wondering why did our appendix shrink over years of non use.... shouldn't it just stay there since it does not effect us positivly or negatively.

 

Thx in advance

[mustang292]

If you had 2 noses, but one didn't work, would you want to keep it? Evolution rids those things that have no use.

[Dak]

because we do not use our appendix, there is no evolutionary pressure on it, ie it is free, by a prosess of random change, to do what it wants -- remain the same, improve, or degrade.

 

in the spirit of the 2nd law of thermodynamics, the appendix has been degrading/atrophying as it is more likely that random changes have a degratory effect, than that they have an inproving effect. so over time the appendix has been getting more and more malformed.

 

it is only when something is in use (eg the heart) that it experiences evolutionary pressure -- if the heart mutates and is worse, then evolution suppresses this change from being passed on. therefore things experiensing evolutionary pressure are prevented from degrading (too much). without evolutionary pressure, things tend to crap out

[swansont]

It uses resources, so smaller is better in that regard. It also is prone to appendicitis if it gets too small, which is bad.

 

This is briefly discussed in Why We Get Sick. The New Science of Darwinian Medicine by Nesse and Williams.

[Bluenoise]

Think about it this way. With no function and thus no natural selection there is no positive force maintaining the presence of this organ. When there is a random mutation between generations that effects this organ there is no force selecting against mutations that might degrade the organ. Since there are far more mutations to genes that could occur that would destroy this organ than maintain it, it's coding eventually looses those regions as they get randomized to oblivion or to surving other usefull functions, and the organ goes.

Not to mention that without a funtion maintaining the organ it is a pointless load on the metabolism and would probably have natural selection acting against it. i.e. evolving a more efficient organism by removal of unnecessary load.

 

At least that's my take on it...

[simple]

Lamarc(k?) stated, incorrectly, that parts not used would shrink in size and eventually dissapear. Are there any examples of non useful body parts that have grown in size... I suppose the wings of an ostrich would be one. But since there is no thought put behind these mutations, what caused those with larger or continually functioning appendixes to not pass on their traits... Since as long as they survived and reproduced I do not know where it could have gone. Or is there a possibility of another subconcious factor, even if it did take up extra resources to create a functioning appendix, would that have been enough to stop it from being passed on.

 

Thanks for all the responses, things are clearing up.

[Newtonian]

because we do not use our appendix, there is no evolutionary pressure on it

With no function and thus no natural selection there is no positive force maintaining the presence of this organ. When there is a random mutation between generations that effects this organ there is no force selecting against mutations that might degrade the organ

This is bad understanding of evolution and biology.Evolution through natural selection does not add/subtract body parts nor leave useless vestiges that were once of importance in a state of atrophy.All of our bodyparts are of neccesity and contribute to the success of our species.

Being unaware of an organs function or the apparent harmless effects of its removal,does not mean it is redundant.There are parts that can be surgically removed in abundance.The fact is our success as a species is fundementally because each part is functioning exactly as it should.Our success is based on millions of years of refining each component as it were.

As science advances we now realise the importance of what we once (in our desperation to prove evolution)considered vestigial.The appendix is an important part of the reticulo-enabthelial system. It helps protect you from gastrointestinal problems in the lower ascending colon.The appendix is crucial during your first months to protect your entire gastrointestinal tract from pathogenic invasion while you were an infant.

You see evolution is good isnt it!!

Woe to us,if in our genetic advancement we decide to remove the genes that make these seemingly insignificant vestiges.Designer babies indeed Guffaw

[Dak]

Evolution through natural selection does not add/subtract body parts

 

i believe we used to have tails?

[swansont]

Read Stephen J Gould's "Eight Little Piggies"

[Mokele]

This is bad understanding of evolution and biology.Evolution through natural selection does not add/subtract body parts nor leave useless vestiges that were once of importance in a state of atrophy.All of our bodyparts are of neccesity and contribute to the success of our species.

 

Incorrect, and you seem to have a bad case of adaptionism going on. Just because something exists does not mean it's an adaptation.

 

For instance, my snakes have legs, or at least leg-bones. Remnants of the pelvis and leg bones are embedded in the body wall, with two small "spurs" (claws) on each side of the cloaca. They serve no significant function that we know of.

 

By your own claim, snakes could not have evolved, since they have lost their legs.

 

Or what about cave-fish which have lost their eyes, yet still retain vestiges in early development?

 

In order for evolution to take place, either producing a part or removing it, there must be variation. If there are no mutations that remove a useless body part without causing massive problems elsewhere in the body or during development, then it will stay around, even if useless.

 

Vestigial organs have already been dealt with in great detail in this thread.

 

Mokele

[simple]

I do not believe their is any educated choices that we have on evolution... those who are fit to survive, survive, and pass on their traits, those who do not survive, die. Then there are those little mutations that do not affect much at all and then one day there is a great environmental change...

 

Like resistance to ampicillan from bacteria... those without the resistance gene die and those with it reproduce, but hopefully it thins the number enough for our white blood cells to do their job.

 

For another example there were mice under that nuclear power plant that had a melt down in russia, or I think it was near there (If someone remembers the name...). Anyway, some of these mice were not killed, they developed a resistance to radiation or something like that, and then they reproduced and now all of the mice in that area are immune. I think that if there was a nuclear war there is a great chance that some humans would survive the radiation by the luck of a mutation, but chances are then all the food near us wood be destroyed or the bomb would hit our house, we would find someone to die, but my point is that we adapt carelessly and luckily, becuase science works, evolution works, and thanks to mutations and genetic shuffling organisms can adapt to almost anything. Life as a whole is saved!

[Hellbender]

For instance, my snakes have legs, or at least leg-bones. Remnants of the pelvis and leg bones are embedded in the body wall, with two small "spurs" (claws) on each side of the cloaca. They serve no significant function that we know of.

 

But don't male boids use their spurs to stimulate the female before/during mating?

[Hellbender]

For another example there were mice under that nuclear power plant that had a melt down in russia, or I think it was near there (If someone remembers the name...)

 

Chernobyl?

 

Anyway, some of these mice were not killed, they developed a resistance to radiation or something like that, and then they reproduced and now all of the mice in that area are immune. I think that if there was a nuclear war there is a great chance that some humans would survive the radiation by the luck of a mutation

 

It would have to be one heck of a mutation to enable a human (or anything) to be able to survive the extreme heat A-bombs cause.

[simple]

It would have to be one heck of a mutation to enable a human (or anything) to be able to survive the extreme heat A-bombs cause.

 

Lol. Im not talking about the heat... but the radiation.. like in the case of a nuclear winter. Probably the chance would be slim... but you never know. and yes Chernobyl, thx.

[Dak]

But don't male boids use their spurs to stimulate the female before/during mating?

 

yup. this is most likely evolution finding a use for something that has atrophied to the point where it no longer performs any other purpouse

 

in no other area is this evolutionary recycling more apparent than in areas involving sex

[simple]

in no other area is this evolutionary recycling more apparent than in areas involving sex

 

man nipples?

[Hellbender]

yup. this is most likely evolution finding a use for something that has atrophied to the point where it no longer performs any other purpouse

 

in no other area is this evolutionary recycling more apparent than in areas involving sex

 

true and true. my point is that although the spurs on boids didn't evolve for the purpose of copulation, they still find use for them.

[Hellbender]

man nipples?

 

Since all vertebrate embryos start out as female, and female mammals of course have nipples, it makes sense that male mammals will retain vestigial nipples becasue they are pretty much neutral. I can't imagine in how they could relate to human copulation....

[Mokele]

But don't male boids use their spurs to stimulate the female before/during mating?

 

Yes, hence why I said no significant use. They've been adapted for sexual purposes, but are by no means essential; all "advanced" snakes reproduce just fine, and a defining characteristic of them is that they lack any pelvic vestiges at all.

 

Mokele

[Hellbender]

Yes, hence why I said no significant[/i'] use. They've been adapted for sexual purposes, but are by no means essential; all "advanced" snakes reproduce just fine, and a defining characteristic of them is that they lack any pelvic vestiges at all.

 

gotcha.

[Guest Mr Scientifi]

If you had 2 noses, but one didn't work, would you want to keep it? Evolution rids those things that have no use.

 

i don't think this is necessarily true...i understand the point you are making however if this were true all of the time, why do males still have nipples?

[Dak]

nipples arent uninportant. nipples are uninportant to males, but are quite inportant to females (or rather, the offspring of the females). men and women initially develope the same, but the presence of androstogene will make small modifications to the foetus, to result in a boy. i guess, as androstogene triggers a complete removal of the womb in boys, it could also trigger a complete removal of the nipples, but what would be the point? is it more efficient for men to have no nipples, or for men to have no nipple-removal prosess in the womb?

 

if women ever stop using their nipples, then nipples will probably atrophy and disappear, but untill then, the fact that females use nipples will create evolutionary pressure for humans to maintain nipples - and as long as man-nipples arent actually detrimental, there will be no selective pressure for men to get rid of their superfulouse chest adornments.

 

ok, i cant resist it any longer, i have to say it...

 

hehe, nipples