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

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.

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

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.

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.