# What is the "core" body format that virtually all mammals, birds and reptiles adhere to? **URL:** \ **Category:** Factual Questions\ **Created:** [August 6, 2015, 5:16am UTC](https://boards.straightdope.com/t/what-is-the-core-body-format-that-virtually-all-mammals-birds-and-reptiles-adhere-to/727133 "2015-08-06T05:16:29Z")\ **Posts on this page:** 8\ **Page:** 2
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [August 8, 2015, 1:58pm UTC](https://boards.straightdope.com/t/what-is-the-core-body-format-that-virtually-all-mammals-birds-and-reptiles-adhere-to/727133/21 "2015-08-08T13:58:22Z")
> [@Blue\_Blistering\_Barnacle](#): > > … > (In humans, the brain \*looks \*very symmetric, but functions tend to preferentially lateralize to one hemisphere or another. This is an advanced “Motie”-like thing. Less cerebral mammals have far more symmetry of function, just as “watchmakers” have more symmetry than “Moties”.) > > … 😕 “Motie?” ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [August 8, 2015, 2:49pm UTC](https://boards.straightdope.com/t/what-is-the-core-body-format-that-virtually-all-mammals-birds-and-reptiles-adhere-to/727133/22 "2015-08-08T14:49:07Z")
In [The Mote in God’s Eye](https://en.wikipedia.org/wiki/The_Mote_in_God%27s_Eye), humanity encounters an alien race on a planet orbiting a yellow sun. The yellow sun is in line with a red giant, and the configuration is nicknamed “the mote in God’s eye”. The alien race is nicknamed the Moties as a result. They are a species that has developed considerable diversity in body format and social function. The Moties are bipedal, roughly humanoid, but most of the Moties have three arms, two on one side and one on the other side, an example of asymetrical body structure. ---
**Author:** ![Nelson\_Pike](https://avatars.discourse-cdn.com/v4/letter/n/c6cbf5/32.png) [@Nelson\_Pike](https://boards.straightdope.com/u/Nelson_Pike)\ **Post date:** [August 8, 2015, 3:29pm UTC](https://boards.straightdope.com/t/what-is-the-core-body-format-that-virtually-all-mammals-birds-and-reptiles-adhere-to/727133/23 "2015-08-08T15:29:49Z")
About the only thing IR from HS and college biology is that the animals listed in OP are _chordates_: they possess a _spinal column_ as a defining characteristic. ---
**Author:** ![Blue\_Blistering\_Barnacle](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/blue_blistering_barnacle/32/3386_2.png) [@Blue\_Blistering\_Barnacle](https://boards.straightdope.com/u/Blue_Blistering_Barnacle)\ **Post date:** [August 8, 2015, 3:45pm UTC](https://boards.straightdope.com/t/what-is-the-core-body-format-that-virtually-all-mammals-birds-and-reptiles-adhere-to/727133/24 "2015-08-08T15:45:26Z")
> [@Leo\_Bloom](#): > > 😕 “Motie?” > [@Nefario](#): > > Are there any left/right asymmetrical “soft” animals? Including invertebrates. > > I know that asymmetry exists in crab, crayfish, lobsters with exoskeletons but I can’t think of any soft invertebrates that are not symmetrical. > > Hmmm…just thought of flounder…but I believe the young are symmetrical. > > A long time ago I read _The Mote in God’s Eye_ about aliens that became asymmetrical as they evolved to build and repair machines. 🆒 Yeah, I mentioned them because Nefario did when he introduced asymmetry into the discussion. And 'cuz I liked the book. Before it was cool. 😉 ---
**Author:** ![Lemur866](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lemur866/32/434_2.png) [@Lemur866](https://boards.straightdope.com/u/Lemur866)\ **Post date:** [August 8, 2015, 5:27pm UTC](https://boards.straightdope.com/t/what-is-the-core-body-format-that-virtually-all-mammals-birds-and-reptiles-adhere-to/727133/25 "2015-08-08T17:27:01Z")
> [@Nelson\_Pike](#): > > About the only thing IR from HS and college biology is that the animals listed in OP are _chordates_: they possess a _spinal column_ as a defining characteristic. But she’s not just talking about chordates, she’s talking about [tetrapods](https://en.wikipedia.org/wiki/Tetrapod)–the branch of vertebrates that crawled up on land 360 million years ago. Lots of fish don’t have limbs, let alone four of them. Tetrapod limbs are modified fins, and the ancestral land-fish that evolved into the tetrapods happened to have four stubby fins that it could use to haul itself through the mud from pond to pond. And so all its subsequent descendants start with a body plan that includes four limbs, even ones that modify the limbs into flippers or have lost all their limbs like snakes. Of course the tetrapod branch of the vertebrates has a lot of similarities to the other vertebrates, and the vertebrates have a lot of similarities to the other chordates. But some chordates only have those features in their larval stage: [Tunicate - Wikipedia](https://en.wikipedia.org/wiki/Tunicate). One theory is that chordates are all originally mostly sessile filter feeders, but the vertebrate branch kept the larval body plan into adulthood. ---
**Author:** ![Nelson\_Pike](https://avatars.discourse-cdn.com/v4/letter/n/c6cbf5/32.png) [@Nelson\_Pike](https://boards.straightdope.com/u/Nelson_Pike)\ **Post date:** [August 8, 2015, 5:51pm UTC](https://boards.straightdope.com/t/what-is-the-core-body-format-that-virtually-all-mammals-birds-and-reptiles-adhere-to/727133/26 "2015-08-08T17:51:15Z")
> [@Lemur866](#): > > But she’s not just talking about chordates, she’s talking about [tetrapods](https://en.wikipedia.org/wiki/Tetrapod)–the branch of vertebrates that crawled up on land 360 million years ago. Lots of fish don’t have limbs, let alone four of them. Tetrapod limbs are modified fins, and the ancestral land-fish that evolved into the tetrapods happened to have four stubby fins that it could use to haul itself through the mud from pond to pond. And so all its subsequent descendants start with a body plan that includes four limbs, even ones that modify the limbs into flippers or have lost all their limbs like snakes. > > Of course the tetrapod branch of the vertebrates has a lot of similarities to the other vertebrates, and the vertebrates have a lot of similarities to the other chordates. But some chordates only have those features in their larval stage: [Tunicate - Wikipedia](https://en.wikipedia.org/wiki/Tunicate). One theory is that chordates are all originally mostly sessile filter feeders, but the vertebrate branch kept the larval body plan into adulthood. OP did not exclude aquatic classes. However, I agree it would be more interesting and challenging to limit the case to tetrapods as you do. ---
**Author:** ![cmyk](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cmyk/32/3353_2.png) [@cmyk](https://boards.straightdope.com/u/cmyk)\ **Post date:** [August 8, 2015, 6:31pm UTC](https://boards.straightdope.com/t/what-is-the-core-body-format-that-virtually-all-mammals-birds-and-reptiles-adhere-to/727133/27 "2015-08-08T18:31:29Z")
> [@Shagnasty](#): > > From the link: > “The length of the duck penis, as mentioned in the tweets, grows to 8 or 9 inches during the summer mating season. In winter, it shrinks to less than an inch.” > > Same here (more or less). I am going to start telling everyone that I am “hung like a duck”. The link says _inches_, not _centimeters_. ---
**Author:** ![Stoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/stoid/32/272_2.png) [@Stoid](https://boards.straightdope.com/u/Stoid)\ **Post date:** [August 9, 2015, 4:44pm UTC](https://boards.straightdope.com/t/what-is-the-core-body-format-that-virtually-all-mammals-birds-and-reptiles-adhere-to/727133/28 "2015-08-09T16:44:13Z")
> [@Nelson\_Pike](#): > > OP did not exclude aquatic classes. > > However, I agree it would be more interesting and challenging to limit the case to tetrapods as you do. I kinda did… I specified mammals, birds, and reptiles. While there are aquatic versions of all three, but they all descend from land versions. [Previous page](https://boards.straightdope.com/t/what-is-the-core-body-format-that-virtually-all-mammals-birds-and-reptiles-adhere-to/727133.md?page=1)