So in Ichtyology class I was learning about the Gas Gland. It's an organ fish use to keep themselves buoyant in water. One type of gas gland extracts Oxygen from capillarries to inflate the gland, and then releases it back into the blood supply to lower it's body in the water. I was thinking that the gas gland was probably what had evolved into the lung and asked my proffessor if that's where it evolved from. He didn't seem to know but thought that it seems like the only thing that the lung probably did evolve from. So what does everybody think about that? I thought it was pretty cool for an organ to go from controling buoyancy, to allow life to go even higher and emerge from the water and have a whole new world open up to it.

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That sounds like a pretty decent idea. Its unfortunate that the fossil record makes it difficult to verify transitional states of cells and internal organs. What about lungfish and other partially amphibious critters?
You're absolutely onto something. There are actually a few fish such as gars, bichirs and lungfish who have vascularized gas bladders which work as primitive lungs.
Sounds plausible - evolution certainly works like that.
I've used my lungs the way I imagine a fish uses its gas gland when I used to scuba dive. Once I achieved neutral buoyancy with my equipment I could take a deep breath in to go up and exhale all the way out to go down. It also seems as if oxygen (and some other things) are being handled by our systems in more or less the same way.
I've studied under a zoologist who stated as much. It performs almost the exact same function as a lung so there's a good chance that the lung followed from it.

Given the ad hoc way that virtually every multicellular creature appears to have been put together, it's not at all unlikely that the gas bladder was simply repurposed.

It is, of course, also totally possible that it didn't. The anableps fish has two sets of eyes that evolved separately, i.e. one set is not just another copy the other.

Probably the best analysis would be to look for the encoding regions and at the actual code for the gas bladder and the lungs and see if they match up in any way.
I've seen the anableps at the zoo the other day. Very cool creatures. I thought the pupil was split horizontally in each eye.
I've heard the idea somewhere but can't recall where off hand. It does seem plausible.
It ls an example of co-option in which a structure used for one function evolves into another function. The eye is an example, which evolved from a light sensitive spot in primative cells.
These was Darwin original idea. But we have studied the ontogeny, found the fossils and developed a different tesis:
- Lung and gas gland evolved independently.
Lungs develop from ventral tissue and are a paired structures, gas bladders from dorsal tissue and are always a single structure.
Lungs are actually older in time than gas bladders. Lungs evolved in fishes living in muddy waters, and these fishes were the ancestors of all actual fishes (and tetrapods, including us). But they both evolved from similar structures. Some fishes have many bag like simple organs in the first part of the digestive tract, with different capacities to capture oxigen. These fishes also live in muddy waters, where obtain oxygen from water can be a challenge.

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