# Asymetrical Animals? **URL:** \ **Category:** Factual Questions\ **Created:** [January 23, 2023, 9:06pm UTC](https://boards.straightdope.com/t/asymetrical-animals/978678 "2023-01-23T21:06:56Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Turek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/turek/32/18782_2.png) [@Turek](https://boards.straightdope.com/u/Turek)\ **Post date:** [January 24, 2023, 8:17pm UTC](https://boards.straightdope.com/t/asymetrical-animals/978678/21 "2023-01-24T20:17:03Z")
Many owls’ ears are asymmetrically positioned, to allow them to better pinpoint sound sources. ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [January 24, 2023, 8:34pm UTC](https://boards.straightdope.com/t/asymetrical-animals/978678/22 "2023-01-24T20:34:47Z")
Of course, there’s a Wiki page for this. > **[List of animals featuring external asymmetry](https://en.wikipedia.org/wiki/List_of_animals_featuring_external_asymmetry)** > > Pages for logged out editors learn more > > > This is a list of animals that markedly feature external asymmetry in some form. They are exceptions to the general pattern of symmetry in biology. In particular, these animals do not exhibit bilateral symmetry which permits streamlining and is common in animals. > The crossbill has an unusual beak in which the upper and lower tips cross each other. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [January 25, 2023, 1:04am UTC](https://boards.straightdope.com/t/asymetrical-animals/978678/23 "2023-01-25T01:04:44Z")
I’ll just point out there are multiple geometric notions of “symmetry”. Starfish and sand dollars are not _bilaterally_ symmetrical. To a gross approximation they are radially symmetrical. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [January 25, 2023, 1:13am UTC](https://boards.straightdope.com/t/asymetrical-animals/978678/24 "2023-01-25T01:13:08Z")
> [@LSLGuy](#): > > Starfish and sand dollars are not _bilaterally_ symmetrical. From an evolutionary standpoint, starfish are interesting. Radial symmetry antedates bilateral symmetry. Starfish fall among _Bilateria_, the larvae are not radially symmetric. The adults are a secondary return to radial symmetry. We have _Porifera_ (sponges) and _Placozoa_ without any symmetry. Then _Cnidaria_ (jellyfish etc.) and _Ctenophora_ (comb jellies) with radial symmetry. Other animals fall under _Bilateria_, descended from a common ancestor that evolved bilateral symmetry. Within _Bilateria_ there are some interesting cases like the adult starfish that returned to a radially symmetric body plan, and molluscs with spiral shells. As well as countless examples of more minor deviations from bilateral symmetry. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [January 25, 2023, 1:13am UTC](https://boards.straightdope.com/t/asymetrical-animals/978678/25 "2023-01-25T01:13:36Z")
A prior related thread. > [@Which animals do not have external bilateral symmetry?](https://boards.straightdope.com/t/which-animals-do-not-have-external-bilateral-symmetry/922259/1): > > In the column about why internal organs are not symmetric within the body, Cecil mentions that 99% of animal species are externally symmetric. Which ones are not? ---
**Author:** ![Yllaria](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yllaria/32/3452_2.png) [@Yllaria](https://boards.straightdope.com/u/Yllaria)\ **Post date:** [January 25, 2023, 1:18am UTC](https://boards.straightdope.com/t/asymetrical-animals/978678/26 "2023-01-25T01:18:39Z")
> [@silenus](#): > > But aren’t flounders symmetrical when hatched? They get over it. ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [January 25, 2023, 12:12pm UTC](https://boards.straightdope.com/t/asymetrical-animals/978678/27 "2023-01-25T12:12:56Z")
> [@LSLGuy](#): > > Starfish and sand dollars are not _bilaterally_ symmetrical. Strictly speaking, anything radially symmetrical is _also_ bilaterally symmetrical. It’s just not the maximum degree of symmetry they have. But in any case, adult sand dollars (unlike other urchins) are secondarily bilateral, not purely radial. Their anus has migrated off to one side, and they have preferential fronts and backs. ---
**Author:** ![2\_More\_Bits](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/2_more_bits/32/4148_2.png) [@2\_More\_Bits](https://boards.straightdope.com/u/2_More_Bits)\ **Post date:** [January 25, 2023, 4:20pm UTC](https://boards.straightdope.com/t/asymetrical-animals/978678/28 "2023-01-25T16:20:22Z")
[[Album] Imgur: The magic of the Internet ![](https://i.imgur.com/PAj7u1b.jpeg?fb "Imgur: The magic of the Internet") ](https://imgur.com/a/BNH9CbY) How about another bird (Red Crossbill) ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [January 25, 2023, 4:32pm UTC](https://boards.straightdope.com/t/asymetrical-animals/978678/29 "2023-01-25T16:32:13Z")
There are good accounts of symmetry in the evolution of development here: > **[Bilateria](https://en.wikipedia.org/wiki/Bilateria)** > > Pages for logged out editors learn more > > > Triploblasts Lankester, 1873 > The Bilateria /baɪləˈtɪəriə/ or bilaterians are animals with bilateral symmetry as an embryo, i.e. having a left and a right side that are mirror images of each other. This also means they have a head and a tail (anterior-posterior axis) as well as a belly and a back (ventral-dorsal axis). Nearly all are bilaterally symmetrical as adults as well; the most notable exception is the echinoderms, which achieve secondary... > **[Symmetry in biology](https://en.wikipedia.org/wiki/Symmetry_in_biology)** > > Pages for logged out editors learn more > > > Symmetry in biology refers to the symmetry observed in organisms, including plants, animals, fungi, and bacteria. External symmetry can be easily seen by just looking at an organism. For example, take the face of a human being which has a plane of symmetry down its centre, or a pine cone with a clear symmetrical spiral pattern. Internal features can also show symmetry, for example the tubes in the human body (responsible for transporting gases, ... ---
**Author:** ![Gyrate](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gyrate/32/3588_2.png) [@Gyrate](https://boards.straightdope.com/u/Gyrate)\ **Post date:** [January 25, 2023, 4:44pm UTC](https://boards.straightdope.com/t/asymetrical-animals/978678/30 "2023-01-25T16:44:19Z")
“I went to a planet where the native lifeforms had no bilateral symmetry, and all I got was this lousy F-shirt.” ---
**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:** [January 25, 2023, 10:25pm UTC](https://boards.straightdope.com/t/asymetrical-animals/978678/31 "2023-01-25T22:25:50Z")
> [@MrDibble](#): > > Strictly speaking, anything radially symmetrical is _also_ bilaterally symmetrical. It’s just not the maximum degree of symmetry they have. Not necessarily. The letter S, for instance, or a swastika shape, is radially symmetric, but not bilaterally symmetric. ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [January 26, 2023, 4:32am UTC](https://boards.straightdope.com/t/asymetrical-animals/978678/32 "2023-01-26T04:32:31Z")
No. Those have two- and four-fold **rotational** symmetry, they are not radially symmetrical. Rotational symmetry has _axes_ of symmetry, radial symmetry has _planes_ of symmetry. [![](https://study.com/cimages/multimages/16/circle_with_rotational_and_radial_symmetry.png) ](https://study.com/cimages/multimages/16/circle_with_rotational_and_radial_symmetry.png) ---
**Author:** ![JohnGalt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johngalt/32/184_2.png) [@JohnGalt](https://boards.straightdope.com/u/JohnGalt)\ **Post date:** [January 26, 2023, 4:48am UTC](https://boards.straightdope.com/t/asymetrical-animals/978678/33 "2023-01-26T04:48:58Z")
I seem to recall something Carl Sagan wrote in one of his earlier books, about humans populating a distant planet, and discovering copious amounts of plant life and animals that could be used for food. He mused that the humans could be disappointed when they find that on that planet the DNA strands were twisted in the opposite direction from ours, and were thus indigestible, to great disappointment. (Frankly I don’t know if that’s a real thing; is it?) ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [January 26, 2023, 7:47am UTC](https://boards.straightdope.com/t/asymetrical-animals/978678/34 "2023-01-26T07:47:12Z")
> [@JohnGalt](#): > > Frankly I don’t know if that’s a real thing; is it? Yes, [chirality](https://en.wikipedia.org/wiki/Chirality#Biology) in biochemistry is a real thing. And enantiomers can have very different biological effects. I don’t know the specifics of DNA chirality well enough to know if e.g only the helix could be opposite but the amino acids all still can have the same chirality as ours, in which case it would still be perfectly digestible. But we don’t generally get most of our nutrient intake from DNA. It’s the chirality of the amino acids themselves in proteins, as well as that of sugars, that would have more of an effect. And yes, mirrored aminos and sugars would fuck us over, bigtime. ---
**Author:** ![Tibby](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tibby/32/17030_2.png) [@Tibby](https://boards.straightdope.com/u/Tibby)\ **Post date:** [January 26, 2023, 8:09am UTC](https://boards.straightdope.com/t/asymetrical-animals/978678/35 "2023-01-26T08:09:35Z")
The Honey Badger subspecies _signata_ is bilaterally symmetrical in other respects but has 2 molars on its left lower jaw, and only 1 on the right. ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [January 26, 2023, 8:18am UTC](https://boards.straightdope.com/t/asymetrical-animals/978678/36 "2023-01-26T08:18:12Z")
Too late to edit, but the wiki on Mirror Life is a good start to the concept: > **[Mirror life](https://en.wikipedia.org/wiki/Mirror_life)** > > Mirror life (also called mirror-image life) is a hypothetical form of life with mirror-reflected molecular building blocks. The possibility of mirror life was first discussed by Louis Pasteur. Although this alternative life form has not been discovered in nature, efforts to build a mirror-image version of biology's molecular machinery are already underway. > Many of the essential molecules for life on Earth can exist in two mirror-image forms, referred to as "left-handed" and "right-handed", but l... As far as I’m aware, we don’t know the chirality of the amino acids we’ve detected in space, but [we have detected](https://www.sciencealert.com/scientists-just-detected-this-life-forming-molecule-in-interstellar-space-for-the-first-time) at least one chiral organic molecule there, so chirality may be universal and Sagan’s scenario may not be likely. Or for every planet, it may be 50/50 -[the Murchison meteorite contains a mix of amino chiralities](https://en.wikipedia.org/wiki/Murchison_meteorite#Organic_compounds) .I think the jury’s still out on it. ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [January 26, 2023, 9:44am UTC](https://boards.straightdope.com/t/asymetrical-animals/978678/37 "2023-01-26T09:44:13Z")
> [@JohnGalt](#): > > on that planet the DNA strands were twisted in the opposite direction from ours, and were thus indigestible > [@MrDibble](#): > > Yes, [chirality](https://en.wikipedia.org/wiki/Chirality#Biology) in biochemistry is a real thing. Chirality in DNA wouldn’t render food indigestible, would it? ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [January 26, 2023, 9:58am UTC](https://boards.straightdope.com/t/asymetrical-animals/978678/38 "2023-01-26T09:58:55Z")
Not if it’s just the helix that’s chiral, no. But if the sugars that are in it are mirrored, there’s problems, as far as I’m aware. But like I said, the digestibility of DNA itself isn’t a major concern, it’s hardly a major nutrient for humans (prurient jokes aside) But like I said, I’m not sure how mirrored DNA codes to peptide chains, if it requires mirrored aminos, or what the story is there. ---
**Author:** ![Peter\_Morris](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/peter_morris/32/359_2.png) [@Peter\_Morris](https://boards.straightdope.com/u/Peter_Morris)\ **Post date:** [January 26, 2023, 12:49pm UTC](https://boards.straightdope.com/t/asymetrical-animals/978678/39 "2023-01-26T12:49:16Z")
I understand it’s proteins that are the problem. > **[Chirality and Handedness of Protein Structures - PubMed](https://pubmed.ncbi.nlm.nih.gov/29544434/)** > > In proteins, the polypeptide chain forms a number of right- and left-handed helices and superhelices, right- and left-turned hairpins, and some other structures that are nonsuperimposable, although they are not mirror images of each other as the... ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [January 26, 2023, 2:47pm UTC](https://boards.straightdope.com/t/asymetrical-animals/978678/40 "2023-01-26T14:47:19Z")
> [@Napier](#): > > Chirality in DNA wouldn’t render food indigestible, would it? > [@MrDibble](#): > > I’m not sure how mirrored DNA codes to peptide chains, if it requires mirrored aminos, or what the story is there. Life on earth uses L-amino acids and D-sugars, with the chirality of DNA deriving from the sugars in the backbone of the spiral. If we tried to eat mirror life, as @MrDibble said the digestibility of proteins is certainly an issue, the direct digestibility of DNA probably is not, I’m not sure about sugars themselves. But the underlying question is whether partially-mirrored life is possible, where DNA & sugars are mirrored but proteins are not. The relationship appears to be arbitrary in life. There is no obvious reason that different translation machinery (enzymes and transfer RNA) could not exist to translate mirrored DNA in non-mirrored protein or vice versa. There’s nothing obvious that forbids life with L-amino acids and L-sugars. But there may be a deeper relationship that ties L-amino acids to D-sugars. There are some wild theories about the origin of homochirality on earth. It may not have been a chance event, and it may have arisen before life evolved. Amino acid precursors with enantiomeric excess (ee) may have been delivered on asteroids and comets, with the ee subsequently amplified on Earth abiotically. The extraterrestrial ee may have derived from circularly polarized light. > **[How did life begin? It’s Chemistry 101, but in space](https://arstechnica.com/science/2018/02/how-did-life-begin-its-chemistry-101-but-in-space/)** > > Better access to chemistry from space keeps changing how we understand life. If these theories about the origin of homochirality on Earth are correct, there may be deterministic prebiotic mechanisms that relate L-amino acid chirality to D-sugar chirality, as described here: > **[L-amino acids catalyze the formation of an excess of D-glyceraldehyde, and...](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2851924/)** > > Previous work by us, and others, has shown that the formation of amino acids on prebiotic earth with the geometric arrangement called the L configuration can be understood. Some meteorites of the carbonaceous chondritic type deliver unusual amino... [Previous page](https://boards.straightdope.com/t/asymetrical-animals/978678.md?page=1) [Next page](https://boards.straightdope.com/t/asymetrical-animals/978678.md?page=3)