# 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:** 14\ **Page:** 3
**Author:** ![silenus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/silenus/32/166_2.png) [@silenus](https://boards.straightdope.com/u/silenus)\ **Post date:** [January 26, 2023, 3:03pm UTC](https://boards.straightdope.com/t/asymetrical-animals/978678/41 "2023-01-26T15:03:36Z")
“Reverse” sugars and such are a major plot point in one of Spider Robinson’s _Callahan’s Saloon_ stories. Turns out the mirror image of complete rotgut is sublime. ---
**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, 6:08pm UTC](https://boards.straightdope.com/t/asymetrical-animals/978678/42 "2023-01-26T18:08:57Z")
Thanks for all the replies. I’m not sure if Sagan was talking about DNA, or more likely as @MrDibble explained, mirrored amino acids. If it was in one of Sagan’s books, I read it a few decades ago. ---
**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, 6:26pm UTC](https://boards.straightdope.com/t/asymetrical-animals/978678/43 "2023-01-26T18:26:19Z")
It’s unlikely that Sagan was distinguishing the two. The usual discussion of “mirror life” assumes that everything is mirrored - both the chiral centers in peptides and the chiral centers in sugars/DNA. For Sagan’s rhetorical purposes, talking about the spiral of DNA going the other way is much easier to grasp than explaining how carbon atoms are chiral centers. I’ve honestly never heard anyone ask before if it’s possible for hypothetical life to mirror one and not the other - it was a new one on me. For synthetic biology purposes, you would certainly mirror everything. Natural enzymes in life on earth are made with L-amino acids and have D-sugars as substrates. You can just mirror everything to make an enzyme with D-amino acids that has L-sugars as substrates. But an enzyme made with L-amino acids that has L-sugars as substrates is a different enzyme, not a mirror image. ---
**Author:** ![Retzbu\_Tox](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/retzbu_tox/32/11829_2.png) [@Retzbu\_Tox](https://boards.straightdope.com/u/Retzbu_Tox)\ **Post date:** [January 26, 2023, 6:48pm UTC](https://boards.straightdope.com/t/asymetrical-animals/978678/44 "2023-01-26T18:48:50Z")
> [@drad\_dog](#): > > There’s an old limerick about someone with a corkscrew part of their anatomy. It ends with the words “Left hand thread” That is totally ridic… > **[Does a pig have a corkscrew-shaped penis?](https://www.straightdope.com/21341237/does-a-pig-have-a-corkscrew-shaped-penis)** ---
**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, 8:34pm UTC](https://boards.straightdope.com/t/asymetrical-animals/978678/45 "2023-01-26T20:34:40Z")
Pshaw. [Lake ducks](https://en.wikipedia.org/wiki/Lake_duck#Penis) have a corkscrew penis with a spiny base and bristly tip… ---
**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, 9:18pm UTC](https://boards.straightdope.com/t/asymetrical-animals/978678/46 "2023-01-26T21:18:47Z")
I have the same affliction. Helps when I need to open a bottle of Merlot. ---
**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 26, 2023, 10:36pm UTC](https://boards.straightdope.com/t/asymetrical-animals/978678/47 "2023-01-26T22:36:32Z")
As I understand it, the terminology originated with sugars, specifically with glucose AKA dextrose, and its mirror-image levtrose. You can distinguish between them in the lab by dissolving them in water, and then shining polarized light through the solution: If you shine polarized light through glucose, the polarization axis rotates to the right, and if you shine it through levtrose, it rotates to the left (hence the name). But this polarization rotation isn’t uniform for all sugars, or for all amino acids. Rather, every other biological molecule has a handedness defined in terms of how it reacts with dextrose versus how it reacts with levtrose. So it’s not a coincidence that all of the sugars, or all of the amino acids, have the same “handedness”, because to a large degree, that’s just how they’re defined. And mirror-life, living in an ecosystem of other mirror-life, should work exactly like ours. It’s quite likely that if we find another life-bearing planet, its biochemistry will be consistent in its handedness, because molecules that work well with other molecules will be evolutionarily favored, and if two kinds coexist for a time, eventually (fairly quickly) one will outcompete the other. But every planet would be a different coinflip, and it would be very difficult to tell which is which without recovering samples and testing them in a lab. (nitpick, by the way: One of the 20 amino acids common in Earthly life is actually mirror-symmetric, and hence is neither left nor right) ---
**Author:** ![Lucas\_Jackson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lucas_jackson/32/303_2.png) [@Lucas\_Jackson](https://boards.straightdope.com/u/Lucas_Jackson)\ **Post date:** [January 26, 2023, 10:44pm UTC](https://boards.straightdope.com/t/asymetrical-animals/978678/48 "2023-01-26T22:44:25Z")
> [@silenus](#): > > But aren’t flounders symmetrical when hatched? Yes, but I wonder, are there left and right handed flounders? ---
**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, 10:59pm UTC](https://boards.straightdope.com/t/asymetrical-animals/978678/49 "2023-01-26T22:59:29Z")
> [@Chronos](#): > > every planet would be a different coinflip The problem with “chance” theories connected with the emergence of life is that in a racemic mixture of precursors it’s much more difficult for nucleic acid polymers to form at all, so you don’t get both mirror image forms of biological molecules both arising and one form of life by chance outproliferating the other - you get nothing at all. Deterministic theories are gaining credibility. It’s a really interesting area of research - there are some wild ideas about the possible extrraterrestrial origins of a small enantiomeric excess and how that could then have been amplified _before_ life evolved. Check out the Ars Technica article I linked above (non-technical), and there’s a more technical review of abiotic amplification theories here: > **[The Origin of Biological Homochirality](https://cshperspectives.cshlp.org/content/11/3/a032540.full)** > > A new type of review journal, featuring comprehensive collections of expert review articles on important topics in the molecular life sciences ---
**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 26, 2023, 11:12pm UTC](https://boards.straightdope.com/t/asymetrical-animals/978678/50 "2023-01-26T23:12:11Z")
Eh, that article is kind of a mess. It makes a big deal of a chiral molecule being detected in space, but that means nothing, unless we can tell which chirality (or more likely, chiralities) it is, which it eventually admits that we can’t. It also claims that the 2016 observation was the first discovery of a chiral molecule in space, even though the article tells of several much earlier discoveries. And saying that “chirality comes from space” doesn’t help anything, unless you can say why there would be chirality in space, and the only mechanism for that that the article proposes is circularly-polarized ultraviolet light. Which is pretty much only going to come from neutron stars (you need extremely strong magnetic fields to produce circularly-polarized light of that short a wavelength), none of which are all that close to us. ---
**Author:** ![silenus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/silenus/32/166_2.png) [@silenus](https://boards.straightdope.com/u/silenus)\ **Post date:** [January 26, 2023, 11:12pm UTC](https://boards.straightdope.com/t/asymetrical-animals/978678/51 "2023-01-26T23:12:42Z")
Yes. Per Wiki: _Larval flounder are born with one eye on each side of their head, but as they grow from the larval to juvenile stage through [metamorphosis](https://en.wikipedia.org/wiki/Metamorphosis), one eye migrates to the other side of the body. As a result, both eyes are then on the side which faces up. The side to which the eyes migrate is dependent on the species type._ ---
**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 27, 2023, 11:39am UTC](https://boards.straightdope.com/t/asymetrical-animals/978678/52 "2023-01-27T11:39:29Z")
> [@Lucas\_Jackson](#): > > Yes, but I wonder, are there left and right handed flounders? Don’t be ridiculous - flounders don’t have hands. ---
**Author:** ![markn\_1](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@markn\_1](https://boards.straightdope.com/u/markn_1)\ **Post date:** [January 27, 2023, 11:05pm UTC](https://boards.straightdope.com/t/asymetrical-animals/978678/53 "2023-01-27T23:05:30Z")
Then how do they write fan mail? ---
**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 27, 2023, 11:56pm UTC](https://boards.straightdope.com/t/asymetrical-animals/978678/54 "2023-01-27T23:56:55Z")
Rocky, is that you? [Previous page](https://boards.straightdope.com/t/asymetrical-animals/978678.md?page=2)