The Human Tail - An Atavism
It may surprise some of you to know that we as humans have a tail! I can imagine the potential disarray this may cause for skeptics or those pertaining to certain religious views; however, it's not that hard to believe that we have a tail.
Don't scramble for your lower backs just yet - what I mean is, at some point during our embryo stage we have a distinct tail structure which is later removed by our immune system.
It shouldn't be that big of a surprise. We do have a tailbone after all, so it seems fitting to think that we should also have a tail, or perhaps have had a tail.
The Coccyx
Some of you might be thinking that it's just called a tailbone and it really has nothing to do with the presence of a tail.
The tailbone, or coccyx, is actually the remnant of a vestigial tail. A vestigial trait or vestige is a rudimentary structure compared to the same complex structure in other animals. A vestige can have no function or minor functions that are inessential and point to a different original purpose.
A previous evolutionary purpose which we no longer require can be easy to visualize for a tail. A tail would have greatly enhanced our balance and thus our ability to escape predators and become better gatherers/predators ourselves. Nowadays balance is not as integral to our survival, and a tail would likely be a waste of resources.
That's all nice and dandy, but how do we know it's a vestigial trait?
The coccyx is composed of four fused caudal membranes found at the base of the spine where most other mammals and primates have a tail. We as humans are some of the only vertebrates that lack an external tail as an adult, along with a few other primates.
The most important features of a tail are balance and the ability to grasp objects, something that our coccyx doesn't provide. It does have a few minor functions, mainly being an attachment to tendons, ligaments and muscles, but it is not required for things like sitting and walking. You can get the coccyx surgically removed if you suffer from pain in the coccyx (coccydynia).
Embryo Tail Development
At about four to five weeks, the human embryo has 10-12 developing tail vertebrae, along with other complex tissues related to the development of the spinal cord, vertebral column, cartilage and bones, among others. After the eighth week, vertebrae 6-12 have been eliminated via cell death and vertebrae 4 and 5 are being regressed. The immune system attacks and digests the tail cells using white blood cells (macrophages) which are normally responsible for ingesting invading pathogens like bacteria.
The following link highlights the process nicely:
The Human Tail
Now here's where it gets interesting: some of us have retained that tail! Exactly how they retained it is not within the scope of this article, although some methods of gene activation/inactivation are caused by mutations or environmental influences.
Over 100 cases of human tails have been reported in medical literature. About 1/3 of these tails are "pseudo tails" which are usually malformations. The remaining are true tails, made because the absorption of the embryonic tail was not complete or did not occur at all.
How can we tell?
The easy way is that pseudo tails can't move. A true tail can.
True tails also contain a complex bundle of nerve fibers, blood vessels and connective tissue. These tails are covered by normal skin with hair follicles, sweat glands and sebaceous glands. Pseudo tails aren't. True tails can also be inherited and can contain cartilage and vertebrae.
What can we take from this?
This sort of phenomenon isn't that uncommon. Other examples include hind legs on whales and snakes, extra toes on horses and teeth in chickens.
But one thing you can keep in mind is that this only occurs based on your evolutionary ancestors' traits. That's what an atavism is - the reappearance of a lost trait not observed in the parents or recent ancestors of an organism. The trait is specific to a remote evolutionary ancestor. The above examples all remain true to standard phylogenetic trees (which are based on similar traits and molecular sequences).
In other words you'd be hard-pressed to find a mammal with feathers, primates with degenerate wings or arthropods with backbones, vestigial or atavistic. A single case of this occurring would bring a potential debunking of evolution.
The fact that we do have such a trait is not nearly enough to prove evolution on its own, but combine it with all of the other aspects that provide evidence and it can be a regular clincher. For now though, the human tail only provides yet more evidence for the theory.
Personally, I find believing in tales of humans being made in the image of an all-powerful deity that is perfect and yet creates a flawed-creation, punishes its creation for being flawed and to top it off calls it "justice" is too much for me. But that's for another Hub.
As for Evolution? It doesn't seem to be such a far-fetched 'tail' after all.
Comments
- AUTHOR
Haha, but the tail (sort of) prevents a Super Saiyan transformation John! Or at least they only transformed when they lost their tails... either way, I would avoid the full moon if I had a tail.
That's a good question about the chimps and bonobos having tails. I'm sure there have been cases of it, but it's such a rare occurrence in humans (more than 100 reported cases in medical literature), finding it in chimps and bonobos would be even more unlikely. All mammals have tails during their development, so it's very probable that the other apes may also have their cases of atavistic tails.
I don't have any problem with people undertaking a spiritual search for answers. There are an infinite number of possibilities for our creation, the purpose of such a creation, our next steps after life (if any). These are good questions to explore with diligence and honesty. However, I don't believe the mainstream religions are capable of answering such questions without breaching logic or consistency in their texts and beliefs. It's very unlikely to believe the core Christian beliefs without going through a number of mental loops, for instance. I haven't watched the video yet but I do know, for instance, that Collins believes life begins at conception. As a scientist this is rather disingenuous - life is a spectrum. The only reason you'd want it to begin at conception is to validate the idea of a soul, or perhaps to make it easier to control women's bodies. But I digress.
To me it's best if we approach these thoughts individually and without blind faith or blind rejection.
I am absolutely fascinated by atavism. I sort of wish I had a tail, perhaps this is because I was raised on too much Dragon Ball Z.
Does anyone know if chimps and bonobos also have atavist tails?
As far as a faith in God I don't see them to be mutually exclusive if you observe the school of thought by Francis Collins. You don't have to betray your logic to search for God, and you don't have to betray your spirit searching for truth in nature.
- AUTHOR
Thanks melpor. I agree, it's a crucial piece of evidence and can be difficult to explain without evolutionary theory.
mrpopo, good hub. Your hub points to another area of evidence that support evolution, atavism. There are plenty more cases of atavism in humans and other animals. Rated up.
Sounds promising mrpopo.
- AUTHOR
Haha, maybe we'll find some way to deal with them that doesn't require running, otherwise I'm probably screwed! Newton had no idea how right he was with his discovery of inertia, not just for non-living objects but also with living aspects like running, work, motivation and life in general really. That tends to get to me - maybe I'll make a Hub on it someday.
But they would find it so tasty! I bet I can run faster than you, especially with zombies after us.
- AUTHOR
I hope not! I kind of like having my brain :P
I know mrpopo they like the brains of scientists but they'll settle for mine at a pinch.
Yes mrpopo hair does do the same including facial hair. Trust you to come up with a scientific explanation. I guess that puts you as number one on the zombie hit list.
- AUTHOR
Ahah, zombies truly exist Rod! By their own "free will" they reject the truth in front of them and worse, try to spread lies about said truths. I certainly see such individuals "eating brains" constantly!
Pretty freaky about the nails growing even after we're dead though. I think I heard hair does the same. Apparently our body loses moisture after death and the skin shrinks, exposing more of the nails/hair follicles.
By the way, I am taking death here as the time directly after all brain function ends. Mind you there could be creationists we should regard as the living dead.
I suppose the weakness of nails is that we have to trim them or they grow out of control. Nails even continue to grow for some time after you are dead. Now THAT is weird.
- AUTHOR
Ah that's the thing Rod. Are nails used to protect the skin's sensitivity or is the sensitivity caused by the nails themselves?
"One theory about fingernails and toenails suggests that they are designed to protect the delicate nail bed. This supposition has been dismissed by many doctors, who point out that people who permanently lose nails develop tougher nail beds. It seems more likely that the delicate tissue or quick under the nail evolved in response to the presence of fingernails, rather than the other way around."
http://www.wisegeek.com/why-do-we-have-fingernails...
Although it could just be your body adapting to a lack of protection and thus toughening the skin. I can't really say. But I agree, I think I'd rather have nails even with their reduced function.
That's kind of neat Bailey. Is this fusion a recent adaptation or is this group a descendant of a transitional form? Either way, pretty cool.
Well, Baileybear, I like having nails. Having lost a nail and have it grow back I got to appreciate them. They're like so many shields against injury and infection or seem that way to me.
mrpopo & rods - I'd say there were claws. Most mammals in Australia have two nails coming out of one toe (two toes fused into 1, but 2 claws still grow, side-by-side). I noticed this in photographs, and at first thought it was an injury, but looked it up, and it's a feature of the 'diprotodentia' group, which includes the marsupials.
Baileybear, I am not sure either when it comes to toenails. I sometimes think of toenails as a kind of protection, an armor plating for the top of the toe. When I lost a fingernail in an industrial accident my finger felt really soft and very much exposed. I was glad when the nail grew back.
Gorillas may live in forested areas but they don't swing from branch to branch. They have no need of a tail. Sure there are creatures that do swing from tree to tree without tails and as you say they are adapted to do so in other ways.
- AUTHOR
That's quite a sad story, Bailey. I can't imagine such treatment on superficial terms. I guess I shouldn't be surprised of the horrors we as humans are capable of.
Thanks Rod. It's only one of the many viable arguments supporting evolution, however I think it makes it much easier to visualize our evolutionary ancestry as opposed to DNA comparisons and fossils. The general public doesn't seem to understand what DNA is anyway and are reluctant in accepting the credibility of fossils. Good point about the tail's use with trees. Though apes also don't have tails and still live amidst trees, it's compensated by other evolutionary adaptations.
A completely useless feature probably doesn't exist because even in certain cases a poison can be a cure. Like sickle cell disease's effectiveness against malaria; despite otherwise being detrimental it still has a function in this certain instance. For the most part toenails don't really have a use for us and look like a waste of resources. They're probably another vestigial feature. Maybe claws previously? I myself have a tendency to grab things with my feet or flick them up from the ground because I am too lazy to reach down, so I guess toenails help with that. I also scratch my feet or legs with my toenails, but otherwise they don't have much function.
Rod, I can't see how toenails on humans have much use either
Good hub mrpopo. Sounds like this remnant of a tail is a good argument for the theory of evolution. A tail is always useful in the trees but not so useful when we stand upright on two legs. Hence very few humans sport tails nowadays but we all have tail bones.
It has a scientific name, but it had name 'werewolf syndrome' because people were treated so badly for being so hairy, they only came out at night. A sad case is a woman Julie Pastrana - she was paraded around as a freak show. She died after giving birth to a child with same condition (and so did the child). Her revolting husband got them stuffed so could still parade them. Someone wrote a beautiful hub about her:
- AUTHOR
Thanks Bailey. I noticed a lot of heated debate lately so I figured I'd write about this intriguing fact. Hopefully it clears up some misconceptions, but some will reject it as evidence regardless of the evidence being right in front of them. I think it's quite an interesting psychological effect. There was a survey about people tending to cling own to their predisposed beliefs despite indisputable evidence being presented to them. There's probably something in that regard related to evolutionary skepticism.
I love the irony in claiming that the tail is a tumour. Tumours are usually caused by genetic mutations, the knowledge of which is based on evolutionary grounds. Ah well, use science to defeat science and call science a lie. Much like using a book as its own evidence for its claim. "How do I know the Bible is true?" "It's the word of God." "How do I know that it's the word of God?" "Because the Bible says so." Absurd to say the least.
Fantastic Hub btw, I especially like the links you've provided. And goodness at the werewolf syndrome. I wonder if that's where the story came from? I think their shaving blades have their work cut out for them though.
Nice hub. Of course, the IDiots say the tail is a tumour & doesn't have a bone. But the tails do have nerve supplies etc & many have bones. I wrote a hub that touched on atavisms. Another fascinating 'blast from the past' is 'werewolf syndrome' - fur on face & body, including in females.
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