Why Would Organisms Lose Obsolete Body Parts?

Evolutionary theory posits that humans evolved from a ancestor common amongst other primates. In this line of descent there are organisms with tails, which is evidenced by the vestigial tailbone in humans. Another example of so called vestigial parts is the non-functional nictitating membrane in the eye, shared in many animals. I've even heard that soon the appendix and pinky toe in humans may disappear due to not being used, though I don't know if these claims are substantiated. I'm wondering how natural selection comes to the phasing out and loss of these body parts? I don't understand how these parts could disappear over time, unless they created a disadvantage significant enough that more organisms lacking the feature would survive and reproduce, so how does this come to be? Could it ever be possible that humans lose their appendix?

Interesting thought.

You can think of it this way...

That pinky toe or appendix is just wasting time and energy and resources in the formation of a fetus if it is hypothetically no longer needed.

Hard to explain.

-SES

reply to post by Tetrarch42


I gotta think the small toe still plays a decent balance role. Granted, we aren't being chased by predators for the most part, but I'd rather have my pinky toes than not!!

It's actually kinda easy to explain. Because these body parts are now obsolete, evolution will no longer keep them in check.

For example, our left arm is VERY useful. If some genetic mutation happened which affected our left arms, that would be weeded out very quickly. When it comes to obsolete body parts, one of the main tenets of evolution - random mutation - will eventually degrade this obsolete body part more and more until it is either non-existent, or until natural selection finds a new use for it.

So I would postulate that in maybe 1000 generations, our Appendix will no longer even exist. Based entirely on the reasoning I put forth above, that is.

reply to post by Tetrarch42

I'm wondering how natural selection comes to the phasing out and loss of these body parts?

It doesn't. Darwin's concept of natural selection as the primary motivating force behind evolution is original, first draft thinking from the 1800's, and even as early as 1860 it was theorized that natural selection was not the whole story. You may as well ask why medical doctors use leeches.

Try reading about punctuated equilibrium theory. It's about 100 years more current.

Fast acting evolution has been observed in many species. For example, here are lizards that developed a new gastrointestinal tract in only 40 years. Here's an experiment in which bacteria spontaneously developed the ability to eat something they previously couldn't. If you want more, go here and go to section 5.

reply to post by LordBucket


Random mutation is a central tenet of the theory of evolution, and random mutations acting upon now-obsolete body parts will - given enough time/generations - likely cause them to degrade, shrink, or disappear, unless nature finds a new use for them. It's not natural selection working, it's random mutation.

I had a dentist tell me back in the 90's that he was seeing children come in that did not have the K9 teeth anymore. He was quite surprised when he first noticed it. He said it also made their mouth a little smaller as a result. Not being a dentist, I couldn't say if that was true or not, but he has been a dentist for over 25 years and was a good family friend. I see no reason why he would lie about it

reply to post by Son of Will

It's not natural selection working, it's random mutation.

Mutation is one proposed mechanism, yes, but why are you responding to my post stating that it's not natural selection by telling me that it's not natural selection?

I guess some people really just need to feel smart.

Here..."the sun rises in the east."

Now go ahead and correct me. Tell me that I'm wrong and that the sun rises in the east.

reply to post by Tetrarch42


I think it is based on the environment that the species lives within, and changes to the environment over long periods of time allowing longterm exposer to environmental changes. Changes I speak of can be radiation exposure from some natural force-magnetic change that effects the gravity of the environment that the species lives in modifying the species way of naturally transporting itself across which ever terrain it must cross (climbing/swinging, swimming long distance walking and deep underEarth caving, more room for radiation exposure when deep). The last change would be longterm exposure to different eating habits. These changes in the intake food of species I would assume modify their digestive systems over long time to fit their new food/energy intake habits.


s&f

The appendix has developed twice in species. This strong suggests it is not "useless."

Currently, the idea is out that it is a bank account for stomach bacteria. For rebooting the gut flora after a sickness.

And since we live in a very clean environment, it probably doesn't occur to us Westerners that living with permanent diarrhea was probably not uncommon in the past. Lack of good bacteria to replace after a "herd" wide sickness purging everyone's guts might actually be catastrophic to that herd. Nobody has the bacteria help replace what is gone, and many people die as a result. But if you have a pouch inside with an account of that bacteria, then you are better off. Your system reboots faster, and you don't die.

The pinky toe is not useless. It is crucial for good balance. It facilitates running and walking long distances. Things you only think are obsolete because you don't run from anything and you don't have walk a savanna or plain every year. This is a fairly recent occurrence, and is really only true for part of the human population.

The wisdom teeth is another favourite of these conversations. Wisdom teeth are more common in groups where rotting teeth is more common. How many of you have stuff put on old cavities in your molars? I bet a good number of you, and you've had them since you were in your twenties at least.

Well now, imagine you live pre-dental care (or post). Those teeth could have rotted out. And then been pushed out by wisdom teeth. Because you NEED back teeth for good survival. Particularly if you need to grind your food more. Like if you have ancestors who lived in climates that might require you to grind grains or raw meats for a significant part of the year. No teeth is a death sentence.

Since many of us with those cavities capped probably started getting those cavities in our teens, this means a death sentence before or during our prime fertility years. Unless of course, you have a backup. Like a set of molars that push out the problem teeth and then grow for the rest of your life.

I still don't understand how these parts would cease to appear in organisms though. Let's assume that for the sake of argument the appendix serves no function whatsoever. Assuming that random mutations result in individuals in a population having smaller/ non-existent appendices, how would this ever lead to appendices disappearing in said population. The lack of an appendix to me, even a completely useless one carries no advantage for survival, and alter reproduction in one individual over another.

reply to post by Tetrarch42


Well, I for one am glad to have my useless body parts. My appendix, tonsils, and adenoids got me lots of gifts, attention, and time out of school.

The extra kidney is good to have also, as a future financial prospect if things get too desperate.

Originally posted by LordBucket
reply to post by Son of Will

 

It's not natural selection working, it's random mutation.

Mutation is one proposed mechanism, yes, but why are you responding to my post stating that it's not natural selection by telling me that it's not natural selection?

I guess some people really just need to feel smart.

Here..."the sun rises in the east."

Now go ahead and correct me. Tell me that I'm wrong and that the sun rises in the east.

It's not just a proposed mechanism, it's almost certainly the mechanism responsible for the OP's comment. I say this because there is already evidence that this occurs all over the place.

I responded to you because your post was completely neglecting this vital component of the Theory of Evolution. I don't need to feel smart, I honestly felt like you didn't understand this. Apologies if I appeared condescending though!

reply to post by Tetrarch42

I still don't understand how these parts
would cease to appear in organisms though.

One generation has it. The next does not. When these changes have been observed, they are not gradual. Look through the links I provided.

For example, first entry on the list:

Content from external source:
5.1.1.1 Evening Primrose (Oenothera gigas)
While studying the genetics of the evening primrose, Oenothera lamarckiana, de Vries (1905) found an unusual variant among his plants. O. lamarckiana has a chromosome number of 2N = 14. The variant had a chromosome number of 2N = 28. He found that he was unable to breed this variant with O. lamarckiana. He named this new species O. gigas.

This "slowly getting smaller over millions of years" version you've been taught in school is based on Darwin's Origin of Species written in 1859. While that mechanism is easily observable during selective breeding, it's not the whole story.

Ahhh, okay sorry. Didn't have much time to read through the pages you provided, I'll give them a thorough reading now.

In our own experience we see people within the same family born shorter, taller, longer legs, shorter toes etc. than their siblings. So we know that children are not carbon copies of their parents, they have differences and we know there can be helpful or neutral mutations.

Evolution and natural selection suggests that over generations if a certain tendency (longer legs, shorter tails) are an advantage for a certain group of the species, the members of the group who have that tendency breed more and although they will have children who go the opposite way, slowly the tendency of of the larger number of future generations will have more and more of that tendency. Of course animals that have the original body shape may prosper as well, so that you have deer and giraffe, two populations that came from the same animal, neither is perfect, both have their niches. And it all happens over centuries with a neck being only a couple inches longer after a several centuries, a wing destined to be lost only milimeters shorter after a thousand years.

Often these body parts are not "lost," the genes just get switched off, again perhaps by accidental mutations that could be harmful unless they come at a different time. But chickens still have teeth if you switch on the gene. Every once in a while a human is born with a very small tail.