# Why are there no six-legged vertibrates? **URL:** \ **Category:** Factual Questions\ **Created:** [August 28, 2011, 5:58pm UTC](https://boards.straightdope.com/t/why-are-there-no-six-legged-vertibrates/594403 "2011-08-28T17:58:54Z")\ **Posts on this page:** 11\ **Page:** 2
**Author:** ![Sailboat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sailboat/32/461_2.png) [@Sailboat](https://boards.straightdope.com/u/Sailboat)\ **Post date:** [August 29, 2011, 3:16pm UTC](https://boards.straightdope.com/t/why-are-there-no-six-legged-vertibrates/594403/21 "2011-08-29T15:16:44Z")
> [@Incubus](#): > > Oh well, so much for my dreams of having a six legged cat. 😛 You CAN have a [six-_toed_ cat](http://en.wikipedia.org/wiki/Polydactyl_cat). ---
**Author:** ![Hari\_Seldon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hari_seldon/32/5173_2.png) [@Hari\_Seldon](https://boards.straightdope.com/u/Hari_Seldon)\ **Post date:** [August 29, 2011, 3:18pm UTC](https://boards.straightdope.com/t/why-are-there-no-six-legged-vertibrates/594403/22 "2011-08-29T15:18:36Z")
> [@Chronos](#): > > A reminder about how evolution works might be in order: Evolution doesn’t cause the emergence of useful traits. Random processes cause the emergence of traits, and if the trait happens to be useful, evolution causes it to stick around. For any question of the form “why don’t we have this trait?”, the general answer is “because that trait never happened to show up to be selected for”. Amen! ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [August 29, 2011, 5:18pm UTC](https://boards.straightdope.com/t/why-are-there-no-six-legged-vertibrates/594403/23 "2011-08-29T17:18:29Z")
> [@Autolycus](#): > > Wait, stop the presses! We can grow tails?! Why hasn’t anybody told me this? How soon? (Seriously though, does that mean humans could grow tails within a couple of generations, or more like a thousand generations?) Humans occasionally grow tails now. A quick google search finds a baby boy born with a tail in India in 2001 (many believed he was a reincarnated Hindu god), a baby girl born with a tail in Cambodia in 2004, and a baby girl born with a tail in China in 2010. Here’s an article about it from the LA Times. > **[What our tails tell us](https://www.latimes.com/archives/la-xpm-2007-feb-15-ed-tails15-story.html)** > > Atavistic incidents, such as humans born with tails, actually bolster the case for Darwinism. This caught my eye: > [@](#): > > It’s not just humans who experience these altered states. Le Page also cites the less cringe-making example of a humpback whale with leg-like appendages that was caught off Canada’s Vancouver Island in 1919. ---
**Author:** ![Blakeyrat](https://avatars.discourse-cdn.com/v4/letter/b/ecd19e/32.png) [@Blakeyrat](https://boards.straightdope.com/u/Blakeyrat)\ **Post date:** [August 29, 2011, 8:28pm UTC](https://boards.straightdope.com/t/why-are-there-no-six-legged-vertibrates/594403/24 "2011-08-29T20:28:45Z")
> [@Blake](#): > > Macropods have evolved a pentapedal posture using their tail as a fifth limb. > Pangolins are tripedal. I think you have these two mixed-up? Macropods (kangaroos) are tripedal, right? Using their thick tail as a “third foot”. In any case, I’m almost certain that Pangolins keep all their feet on the ground at the same time, making them at least quadrupeds, and possibly pentapedes, depending on how they use their tail. ---
**Author:** ![j\_sum1](https://avatars.discourse-cdn.com/v4/letter/j/8baadc/32.png) [@j\_sum1](https://boards.straightdope.com/u/j_sum1)\ **Post date:** [August 30, 2011, 2:02am UTC](https://boards.straightdope.com/t/why-are-there-no-six-legged-vertibrates/594403/25 "2011-08-30T02:02:42Z")
Hmmmph. Someone obviously hasn’t seen Avatar. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [August 30, 2011, 3:10am UTC](https://boards.straightdope.com/t/why-are-there-no-six-legged-vertibrates/594403/26 "2011-08-30T03:10:30Z")
> [@Incubus](#): > > I always thought tails were simply an extension of the spine, really. They’re so common, I’d say we’re in the minority of vertibrates that _dont_ have an exposed tail. A tail - that is, an extension of the body posterior of the anus - is a typical characteristic of vertebrates that is not found in most other phyla. In most phyla, the anus is at or near the posterior end of the body (although there are some exceptions). ---
**Author:** ![Fubaya](https://avatars.discourse-cdn.com/v4/letter/f/c2a13f/32.png) [@Fubaya](https://boards.straightdope.com/u/Fubaya)\ **Post date:** [August 30, 2011, 5:25am UTC](https://boards.straightdope.com/t/why-are-there-no-six-legged-vertibrates/594403/27 "2011-08-30T05:25:49Z")
Where would you put the extra pockets? I wonder if six legs would actually be any better for a vertebrate. I’d like to see a computer model of a six legged animals skeleton while walking/running. In quadrupeds, having limbs toward each end of a flexible backbone forms really useful geometry. Take a look at [this](http://www.cs.bilkent.edu.tr/~culha/cs548/pro/) page and scroll through the pictures and try to imagine another set of legs in the middle. Take a look at that cheetah and how its spine contracts and stretches and the legs utilize every bit of leverage they can from that to produce raw power. This may be an extreme example, but I think the backbone of most quadrupeds act in a similar fashion. That flexibility is important. Now imagine a set of legs in the middle. Any time they have weight on them, they will act as a fulcrum in the middle of the backbone. I think those legs would be the “main” legs, whatever they do is going to affect the spine and determine what the other legs can do, and I think you’d have an animal with less vertebral leverage and flexibility than a four legged one. That means slower, more cumbersome. On the upside, it could stand on it’s front four legs and wag its ass. That would probably be worth it. ---
**Author:** ![drewtwo99](https://avatars.discourse-cdn.com/v4/letter/d/d07c76/32.png) [@drewtwo99](https://boards.straightdope.com/u/drewtwo99)\ **Post date:** [August 30, 2011, 3:30pm UTC](https://boards.straightdope.com/t/why-are-there-no-six-legged-vertibrates/594403/28 "2011-08-30T15:30:50Z")
There was once a website community that I came across reading a list of “internet communities you won’t believe actually exist,” and the entire purpose of the website is to worshipping what they call “boytaurs”, or men with multiple limbs. Some look like centaurs, some look like regular men with extra arms or legs, etc. They treat the photos and stories and authentic, without any bit of acknowledgement that none of them are real. Obviously there are people out there who wish that humans had more than just 4 limbs. I would provide a link, but unfortunately there is a fair amount of adult content on the site, and I’m not sure what the policy is about linking that sort of stuff, so I won’t. But if you are TRULY curious, it is kind of a WTF sort of thing and good for the curious mind, so feel free to google it. ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [September 1, 2011, 12:31am UTC](https://boards.straightdope.com/t/why-are-there-no-six-legged-vertibrates/594403/29 "2011-09-01T00:31:05Z")
> [@Blakeyrat](#): > > I think you have these two mixed-up? No, > [@](#): > > Macropods (kangaroos) are tripedal, right? No. > [@](#): > > Using their thick tail as a “third foot”. Never. Kangaroos walk using 5 limbs. They run with only two in contact with the ground. > [@](#): > > In any case, I’m almost certain that Pangolins keep all their feet on the ground at the same time, making them at least quadrupeds, and possibly pentapedes, depending on how they use their tail. Nope. Pangolins walk on their hind limbs and tails. The front limbs only touch the ground when they are digging or climbing. ---
**Author:** ![dracoi](https://avatars.discourse-cdn.com/v4/letter/d/90db22/32.png) [@dracoi](https://boards.straightdope.com/u/dracoi)\ **Post date:** [September 1, 2011, 2:59am UTC](https://boards.straightdope.com/t/why-are-there-no-six-legged-vertibrates/594403/30 "2011-09-01T02:59:31Z")
> [@Fubaya](#): > > I wonder if six legs would actually be any better for a vertebrate. I’d like to see a computer model of a six legged animals skeleton while walking/running. In quadrupeds, having limbs toward each end of a flexible backbone forms really useful geometry. Six legs would definitely not be useful - you’re exactly right about the spine acting as a spring - but if the extra appendages did something different, that could be good. Bats and birds would probably benefit from four legs and two wings or maybe even four wings to give extra lift and control. A monkey might want four legs and two hands. A vertebrate version of a preying mantis could make a great predator. I’m not saying any of these things are likely to come about, of course, just that they would probably be successful if they ever happened. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 1, 2011, 3:35am UTC](https://boards.straightdope.com/t/why-are-there-no-six-legged-vertibrates/594403/31 "2011-09-01T03:35:20Z")
> [@](#): > > Bats and birds would probably benefit from four legs and two wings or maybe even four wings to give extra lift and control. A recent thread mentioned some early proto-birds, or at least bird-like creatures, that did in fact have four wings. Of course, being built on the normal vertebrate pattern, that meant they didn’t have any limbs left over for other purposes, which may be why that form didn’t take over. [Previous page](https://boards.straightdope.com/t/why-are-there-no-six-legged-vertibrates/594403.md?page=1)