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> (eg. our light sensitive cells point in the wrong direction) Can you expand on that? Are you talking about front-facing eyes vs. birds' eyes? Or something el

> (eg. our light sensitive cells point in the wrong direction) Can you expand on that? Are you talking about front-facing eyes vs. birds' eyes? Or something else like retinal structure?

dtgriscom 3y ago
Retinal structure: https://en.wikipedia.org/wiki/Retina#Inverted_versus_non-inverted_retina https://en.wikipedia.org/wiki/Retina#Inverted_versus_non-inv...
metabagel 3y ago
I had to look this up, and I guess what usrbinbash was referring to was the layout of the retina, which places the rods and cones behind layers of transparent neurons. https://en.wikipedia.org/wiki/Retina#/media/File:Retina-diagram.svg https://en.wikipedia.org/wiki/Retina#/media/File:Retina-diag... Edit: ninja'd
- dekhn 3y ago
  Yet, it doesn't really have a strong impact as it's been determined that humans can see individual photons and we aren't dependant on night vision for hunting.
  - usrbinbash 3y ago
    It doesn't have a strong impact, and the design also doesn't prevent good night vision (the basic structure of a cats eye is similiar, ALL chordata have an inverted neural makeup). But that doesn't mean the setup makes sense, and that is exactly my point. And long term, this has an impact. For example, vertebrate brain size is limited by the simple factor, that we have to put all the connections on the outside. The more neuronal bodies we have, the more connections they require. N <---> N In this clumsy diagram, 2 neurons talk with the connections on the inside. However, vertebrate brains have to do this instead: +--------------+ | | +-> N N <-+ It's easy to see how the second setup becomes prohibitive when more Neurons are added to it. The brains of Protostomia again don't have that problem...they can have the connections on the inside, and the neuron bodies on the outside, aka. the logical setup. Now there are ways around that, eg. Reptile and Bird brains grow in bulbs that theoretically allow sustained growth without the connective layer getting in the way. But similar to the reflective layer in our eyes, this is not a setup that's there because it makes a lot of sense...it's a hack, a workaround for some "legacy system", that is now so enmeshed, it's impossible to change.
usrbinbash 3y ago
https://en.wikipedia.org/wiki/Cephalopod_eye#/media/File:Evolution_eye.svg https://en.wikipedia.org/wiki/Cephalopod_eye#/media/File:Evo... Lefthand is a vertebrate eye, righthand is a squids eye. In Vertebrates (really in all Chordata), the light sensitive "tips" of the sensory cells point inwards, aka. the exact wrong direction. At the base of the cells are the axons (nerve connections) which transmit the information into the brain. Due to the aforementioned orientation, these axons run along the outer layer of our light sensitive cells, and at some point have to travel "invards" towards the brain. At that point there can be no cell bodies, and that's the "visual blind spot" of our eyes. A squids eye doesn't have that problem; all the light sensitive cells point outwards, the axons are at the innermost layer, and connectivity can be achieved without a blind spot (also, they don't need a reflective layer).

> (eg. our light sensitive cells point in the wrong direction) Can you expand on that? Are you talking about front-facing eyes vs. birds' eyes? Or something else like retinal structure?

dtgriscom 3y ago

Retinal structure: https://en.wikipedia.org/wiki/Retina#Inverted_versus_non-inverted_retina https://en.wikipedia.org/wiki/Retina#Inverted_versus_non-inv...

metabagel 3y ago

I had to look this up, and I guess what usrbinbash was referring to was the layout of the retina, which places the rods and cones behind layers of transparent neurons. https://en.wikipedia.org/wiki/Retina#/media/File:Retina-diagram.svg https://en.wikipedia.org/wiki/Retina#/media/File:Retina-diag... Edit: ninja'd

dekhn 3y ago
Yet, it doesn't really have a strong impact as it's been determined that humans can see individual photons and we aren't dependant on night vision for hunting.
- usrbinbash 3y ago
  It doesn't have a strong impact, and the design also doesn't prevent good night vision (the basic structure of a cats eye is similiar, ALL chordata have an inverted neural makeup). But that doesn't mean the setup makes sense, and that is exactly my point. And long term, this has an impact. For example, vertebrate brain size is limited by the simple factor, that we have to put all the connections on the outside. The more neuronal bodies we have, the more connections they require. N <---> N In this clumsy diagram, 2 neurons talk with the connections on the inside. However, vertebrate brains have to do this instead: +--------------+ | | +-> N N <-+ It's easy to see how the second setup becomes prohibitive when more Neurons are added to it. The brains of Protostomia again don't have that problem...they can have the connections on the inside, and the neuron bodies on the outside, aka. the logical setup. Now there are ways around that, eg. Reptile and Bird brains grow in bulbs that theoretically allow sustained growth without the connective layer getting in the way. But similar to the reflective layer in our eyes, this is not a setup that's there because it makes a lot of sense...it's a hack, a workaround for some "legacy system", that is now so enmeshed, it's impossible to change.

usrbinbash 3y ago

https://en.wikipedia.org/wiki/Cephalopod_eye#/media/File:Evolution_eye.svg https://en.wikipedia.org/wiki/Cephalopod_eye#/media/File:Evo... Lefthand is a vertebrate eye, righthand is a squids eye. In Vertebrates (really in all Chordata), the light sensitive "tips" of the sensory cells point inwards, aka. the exact wrong direction. At the base of the cells are the axons (nerve connections) which transmit the information into the brain. Due to the aforementioned orientation, these axons run along the outer layer of our light sensitive cells, and at some point have to travel "invards" towards the brain. At that point there can be no cell bodies, and that's the "visual blind spot" of our eyes. A squids eye doesn't have that problem; all the light sensitive cells point outwards, the axons are at the innermost layer, and connectivity can be achieved without a blind spot (also, they don't need a reflective layer).