There are no humans who can breathe water, but there are humans who can hold their breath much longer than your average human. If a human population was put in a situation where we had to spend a lot of time swimming underwater, those who could hold their breath longer would be more likely to pass their mutation on.
On a slight hijack, I’ve always liked this quote about evolution.
Actually, it might have helped, as it would mean that there was something to eat on land - specifically it might have been worth momentarily beaching yourself to take a snap at the arthropods at the water’s edge.
Well some quakers actually leave their communities and survive the contact with technology. So anything can be adaptable. 
You’re nicer than me. I was going to just steal it.
Wow, that truly is a brilliantly simple description. As is dakravel’s!
I think you may have meant , " Some Amish "… Quakers do not live particularly cloistered existences, whereas Amish or Mennonites do by comparison.
What made it twice as funny is that it seemed to be from a chat log or something. Is that the case?
Props to Squink too.
bash.org is a repository of user-submitted IRC quotes, although as of recently people have been sneaking in AIM and ICQ stuff in there too.
Shows what you know about Mennonites. 
Aww Shucks 
-Thanks for the kind words.
That site had me in tears for an hour.
As far as anyone knows, sure.
Er, there are.
Interesting, but not immediately useful for survival in the immediate environment. As individuals, we can think “oh, it might be nice if I could breathe water!” But evolution doesn’t happen to individuals. It happens to entire populations.
For all we know, some could be. But it would require humans living for a long long periods in aquatic or near aquatic lifestyles. And by that, yes, we mean tens of thousands of years before any appreciable pressure for better adaptability would being to detecably shift the population traits towards those best suited to operate in aquatic environments. But even then that might not involve breathing water. There are many many ways to survive in aquatic environments, and no PARTICULAR solution would have to happen.
This appears to be what happened with whales: land mammals that moved back into an aquatic lifestyle.
There is even a much maligned but not incredibly stupid supposition that at one point the branch of the tree life we would eventually be the fruit of involved mammalian apes who did move to somewhat aquatic lifestyles. This is generally considered to be without much evidence, but it’s an example of the sort of suprises one might well find in any lineage of creatures.
And if I ain’t quick enough, Tamerlane gets to it first.
Tamerlane gives the general consensus of the process by which lungs (and swim bladders) evolved.
From here:
It may be worth mentioning too the concept of exaption: Traits that are evolved for one purpose may later be adapted for some entirely different purpose. For examples, fossils suggest that feathers first evolved as insulation for homeothermic theropod dinosaurs, only later being adapted for flight in the bird lineage. Likewise, lungs were exaptions that allowed for the later evolution of swim bladders.
Colibri: I was taught that that was called “preadaptation.”
Speaking of preadaptation/exaption, legs evolved BEFORE the colonization of dry land (by the 4-legged). Acanthostega was believed to be the first fish to walk on land, until further study showed its “legs” would have been worse than useless out of water. Acanthostega used its leg-like fins to crawl along river bottoms, much as the Coelacanth pictured at the bottom of the page uses its fins to walk along the ocean floor.
BTW, IC and ID are held in slightly lower esteem in the biological sciences community than phrenology, largely because it isn’t a falsifiable hypothesis to say that anything unexplained is a clear case of “Goddidit!”
Same thing, really, but “exaption” tends to be favored by many evolutionists nowadays to avoid the implication that a trait evolved “before it was needed,” as might be construed from “preadaptation.”
See here
And a good idea that is, too! There is so much misinformation floating around, even among folks who accept evolution, that the last thing we need is to give people a reason to misunderstand it.
[aside - and a minor correction 
]
The term exaptation was coined by none other than S. J. Gould, along with Elizabeth Vrba.
See: Gould, S.J./Vrba, E.S. 1982. Exaptation: A missing term in the science of form. Paleobiology 8(1): 4—15.
[/aside]
:smack:
I feel like a fish outa water, but am following the thoughtful answers to my simplistic query with great interest, thank you for all of these posts. Keep ‘em comin’ .
( Get it? Fish outa water? Make no bones about it, when your writer works for scale, it shows. )
What other questions do you have?
Basically, the problem with the scenario in the OP is that fish did not evolve lungs so they could “venture out on the land” (as it is sometimes phrased).
Instead:
-
Fish evolved lungs originally so they could better live in the water; specifically in stagnant water with a low oxygen content. Air has a much higher concentration of oxygen than water, so it’s easier to extract oxygen from it, if you can figure out a way to keep the absorptive surfaces moist. Fish are able to absorb some oxygen through the skin anyway; it was easy enough to develop a sac branching off the mouth that contained highly vascularized skin where air could be held and gases exchanged. The fish continued to live in the water, but would periodically gulp air from the surface, as is often seen in fish living in stagnant water today.
-
Fish didn’t go to the land, the land came to them. That is, the pools where they lived periodically dried out. Those that could breathe air and resist drying out long enough, and had strong enough muscles in there fins (or primitive legs) to push themselves along to the nearest pool that still had water, would survive to produce the next generation. (Today this kind of ability is shown by species like the “walking catfish” that can cover considerable distances on land). These adaptations originally were so the fish could continue living in the water, not gallivant on land. But eventually, some became so good at it they could pursue insects on land at the edge of the pools, and gain a food source not available to other fish.
Many of the steps in this process have parallels in living fish, so it’s really not a difficult scenario to visualize.