I’m a fish. I’m an animal who is captive within an enviroment. I’ve developed in that environment, my planet has never supported any life in another kind of environment.
I flop up out of water. Literally. Do I magically grow a secondary system of processing oxygen, using lungs and bronchii and alveolar gas exchange? No, I don’t. I die from lack of oxygen because my gills cannot handle the lack of flowing water that carries my life-giving oxygen.
So, I die. And cannot live on land. One doesn’t magically adapt for no reason, so - since it is more or less accepted theory that life began in the planet’s oceans, how did the leap to land-based oxygen processing happen? If I were to be a genetic mutant, and somehow be spawned with two radically different sets of breathing equipment, what would POSSIBLY make me want to venture OUT of my primary environment, into a completely alien and potentially deadly one? How could I even KNOW I had that secondary set of breathing apparatus, since it is beyond my ken to know it might come in handy?
You do realize that there are fish today who are capable of spending short amounts of time on land, thanks to rudimentary lung-like apparatuses? Really, this is not a very difficult evolutionary step to explain. It’s quite well documented, in fact.
My understanding is that gills are fragile organs, and will collapse in air.
However, a fish that can tolerate even a little exposure to air will have a better chance to survive than one that cannot, when both are exposed to air. The one which survives has a better chance of passing on more genes (long lifespan=more reproductive opportunities). Of those offspring, some will likely be able to tolerate brief exposure to air, and others won’t. The ones who CAN tolerate air exposure have a better chance of survival, again. In the case of the airbreathing fish we have today, they live in muddy ponds, and if their local pond dries up or otherwise becomes unsuitable, they “walk” on their fins to another pond. A fish that can’t breathe air for even short periods of time doesn’t have that option.
IIRC, lungs didn’t evolve from gills, but from another organ that had evolved for some other purpose. Can’t remember where I learned that, so I don’t have a cite. I’d bet that our friend, Colibiri could clarify that. He usually shows up in these types of threads eventually, although more often in GQ than QD.
•Try everything (even if it ain’t broke)
•Kill everything that doesn’t work.
•Repeat.
Some of those fish swimming in your sea will develop mutations that a) have little effect on their survival chances at sea and b)do affect their ability to tolerate life on dry land. As long as the sea doesn’t dry up, or predators chase the fish out of the shallows onto shore, there’ll be no selective pressure for one sort of fish over the other. Both types will thrive. Only when water is in short supply will the advantage of one type of fish over the other become apparent. The fish without the adaptation will die. That’s your “evolutionary moment.” There is no positive evolutionary force.
That’s about the best, short description of evolution I’ve every seen. Nice job!! If I use it sometime in the future, I’ll try to remember to attribute it to you.
Swim bladders, which are used to maintain buoyancy in ray-finned fishes.
Actually, though, the thinking these days is that lungs came first and swim bladders later. Lungs were just outpocketings in the gut that could hold gas - early fish in anoxic environments ( i.e. drying, muddy ponds in dry seasons ) would gulp air and hold it in the gut and thus acquire enough oxygen through diffusion to skate by, the better the diffusion achieved ( through holding the air longer, developing greater vascularization and more internal surface area ) without compromising yourself in other ways, the more successful you no doubt were in surviving the dry season. And in fact if we look at the fossil geological evidence, all of the five fossil lineages known to have developed lungs came from freshwater environments that appear to have been subject to droughts.
Wow, really?! I guess this just confirms the old saying, “On the Internet, no one knows you’re a fish.” (Wasn’t that it?)
Sorry. Bad geek joke.
To nitpick: before land animals arose from marine life, insects and plants had already populated the land. This didn’t help fish leave the water, of course, since insects breathe atmospheric oxygen by a very different mechanism.
As a rule, no complex anatomical system arises in toto from nothing. It never works that way. They evolve gradually, as distortions or supplements of earlier systems. This applies to lungs, eyes, ears, brains, and everything else. Moreover, the “final” purpose of an organ doesn’t have to have much to do with the original purpose. Evolution has no foresight.
Tadpoles breathe through gills and as frogs develop lungs while maintaining vestiges of their gill structure (as well as the ability to respirate through their skin).
Lynn’s explanation, as well as that offered by others jives of course with what I’ve learned about evolution.
This is a combination of accidental developments AND adaption/survival of fittest? To turn my OP around a lot… I’m a human ( Hah ! ). I walk into the water. I drown. There are perhaps 7 billion people on the planet- not one of them can naturally process water inside of their bodies in a way that allows the absorption of oxygen, right?
Lotsa humans…why are there not accidental mutations? Why is there no need, since living in water might be an interesting adaptation? I’m not trying to play stupid, I’m curious- of amphibians evolved through accident AND causality, why aren’t humans doing the same? ( Either in terms of water and air, or in terms of any other adaptation). Is the timeline too short? In a hundred thousand years, what will we have adapted to? Maybe back into the water?
WAY too short. IIRC, it took several billion years for life to progress from the oceans to land, and that was with organisms that had generations lasting a fraction of the time that human generations last.
If it were to happen, it would more likely happen to a marine-adapted mammal or reptile-- eg, dolphin or sea turtle. A human who could breathe under water would likely be shark food be before he or she could reproduce.
Humans are another kettle of fish entirely. We are no longer evolving naturally. We tend to care for our incompetents, and make sure that they breed, and that the incompetents’ offspring also breed. For instance, in my own family, both my parents are diabetic. I’m also diabetic, and have reproduced. I had complications of diabetes during my pregnancy which would have killed me (and my unborn child) if it hadn’t been for modern medicine. Had I given birth even 50 years before I did, I’m fairly sure (though I have no medical opinion on this) that I would have died, taking my daughter with me. 50 years is an ASTONISHINGLY small amount of time in evolutionary terms when speaking of species that have our lifespans/reproduction cycles. Of course, for mayflies and such, it’s a lot longer. So, I have reproduced, and since my husband is ALSO diabetic, it’s quite likely that our daughter carries diabetic tendencies in her genes. These genes may or may not become activated in her lifetime, depending on various factors, some of which we understand (diet and other lifestyle choices) and some of which we don’t, yet. But the fact remains, “bad” genes have reproduced because medical science allowed me to live through my pregnancy, and produce a live child. Multiply this by however many diabetics have done this, and then multiply THAT by however many people with other defects have been able to survive and reproduce, and you begin to understand my statement about evolving naturally. So we’re evolving. We’re breeding more diabetics, for one thing. There’s no telling where it will end up, because we simply don’t live long enough to observe more than a few generations in our lifespans, and we haven’t been keeping the right sort of records to make a good guess.
Whether or not we should be restricting people’s breeding according to their health is quite another Great Debate, so let’s not even THINK about starting it in this thread.
A little thing called “constraint”. No organism is capable of exhibiting all possible mutations, and all possible mutations will not necessarily arise “when needed”.
Humans are well-adapted to life on land. The mutations that would allow them to go back into the water are likely not even possible given the current sate of our genome.
