4 ms·

Having more limbs is less efficient biomechanically - the creature would need a larger heart to pump blood through al organs, that requires more energy, so such

Having more limbs is less efficient biomechanically - the creature would need a larger heart to pump blood through al organs, that requires more energy, so such creature would need more food. Now, it is known that creatures can lose limbs through evolution, but never gain them, so it is likely that multi-legged species would gradually lose extra limbs over time.

Joker_vD 5y ago
> creatures can lose limbs through evolution, but never gain them Wait, so where did the limbs come from anyway, if they could not be gained?
- Andrew_nenakhov 5y ago
  Early creatures had mady different body plans. We have 4 (all vertebrates), 6 (insects), 8 (arachnids) and multilegged creatures (millipedes), as well as legless creatures like snakes (who had 4 legs before they lost them). It seems that vertebrates have certain period when this layout was 'cast in stone' [1] [1]: https://biology.stackexchange.com/posts/21793/revisions https://biology.stackexchange.com/posts/21793/revisions
  - benfarahmand 5y ago
    Reading your comment made me wonder why we have even numbers of limbs for different body plans. I realized it's due to bilateral symmetry for most organisms must some how be advantageous to asymmetric body plans, but I'm unsure how symmetry is advantageous. What are the evolutionary pressures selecting against asymmetric body plans?
    - Andrew_nenakhov 5y ago
      I'm not really a biologist, but I think this has something to do with the balance: when you move in some direction, it would be extremely disadvantageous to have one side significantly heavier than another. Take two runners, give one a 15 kg weight in one hand, and give another 15 kg weights in both hands (30 kg total). I think the runner with weights in both hands would run faster than the one with one weight. Thus, moving species evolve to be bilaterally symmetric. If the organism has no need to move in certain direction, it doesn't really have bilateral symmetry, like trees or bushes (though big trees generally tend to have their center of mass close to their vertical axis).
goatlover 5y ago
Octopuses mange to do okay. And they seem alien enough for a related species. Cephalopods serve as a good counter to the article.
- Andrew_nenakhov 5y ago
  They are aquatic species. When you remove the necessity to support weight above the hard surface, your options are much more varied. Even jellyfishes or amoebas somehow manage to get by.
- bmitc 5y ago
  It's also interesting to point out that they have three hearts and not just one heart.
TedDoesntTalk 5y ago
> it is known that creatures can lose limbs through evolution, but never gain them Did spiders start with more?

Joker_vD 5y ago

> creatures can lose limbs through evolution, but never gain them Wait, so where did the limbs come from anyway, if they could not be gained?

Andrew_nenakhov 5y ago
Early creatures had mady different body plans. We have 4 (all vertebrates), 6 (insects), 8 (arachnids) and multilegged creatures (millipedes), as well as legless creatures like snakes (who had 4 legs before they lost them). It seems that vertebrates have certain period when this layout was 'cast in stone' [1] [1]: https://biology.stackexchange.com/posts/21793/revisions https://biology.stackexchange.com/posts/21793/revisions
- benfarahmand 5y ago
  Reading your comment made me wonder why we have even numbers of limbs for different body plans. I realized it's due to bilateral symmetry for most organisms must some how be advantageous to asymmetric body plans, but I'm unsure how symmetry is advantageous. What are the evolutionary pressures selecting against asymmetric body plans?
  - Andrew_nenakhov 5y ago
    I'm not really a biologist, but I think this has something to do with the balance: when you move in some direction, it would be extremely disadvantageous to have one side significantly heavier than another. Take two runners, give one a 15 kg weight in one hand, and give another 15 kg weights in both hands (30 kg total). I think the runner with weights in both hands would run faster than the one with one weight. Thus, moving species evolve to be bilaterally symmetric. If the organism has no need to move in certain direction, it doesn't really have bilateral symmetry, like trees or bushes (though big trees generally tend to have their center of mass close to their vertical axis).

goatlover 5y ago

Octopuses mange to do okay. And they seem alien enough for a related species. Cephalopods serve as a good counter to the article.

Andrew_nenakhov 5y ago
They are aquatic species. When you remove the necessity to support weight above the hard surface, your options are much more varied. Even jellyfishes or amoebas somehow manage to get by.
bmitc 5y ago
It's also interesting to point out that they have three hearts and not just one heart.

TedDoesntTalk 5y ago

> it is known that creatures can lose limbs through evolution, but never gain them Did spiders start with more?