TrippyYour post, showing all the extras that one way breathing requires makes my point better than I can.
No it doesn't. It contradicts your point entirely. The only thing that is required if you compare a human lung to an alligator lung is the splitting of an air-way. Something that I'm reasonably confident could be achieved with a single mutation. As to why it hasn't happened?
1. H. Sapiens is a young species.
2. We live in a relatively oxygen rich atmosphere.
3. There is no pressure selecting for it.
Don't forget that the human lung is already divided into lobes. It's not that significant of a re-arrangement.
I suspect you don't understand what I am referring to with my term "binary change" (as contrasted with analog change) so I will clarify with the giraffe, where both are well illustrated.
No, I understood what you meant. You obviously haven't understood my points.
EVOLUTION CAN NOT MAKE BINARY CHANGES.
Actually, as Billvon has also pointed out, it can, and there are a number of examples of this.
In contrast the length of the neck can increase via tiny incremental changes accumulating over thousands of generations. For example the average length of the giraffes in generation n+1 can be 0.1mm longer than the average neck length in generation n. Evolution can (and did) change the length of the neck of giraffes as that is an ANALOGUE CHANGE. I don't know why it happened but perhaps the short necked ancessor of the giraffe liked the taste of the leaves at the top of the short bush it feed on more than the slightly more dusty ones closer to the ground - Why the change occured is not important as it did occur as each tiny stage of that analogue change gave a slight benefit.
Giraffe neck length is A) Irrelevant, B) A red herring, and C) Not the only adaptation that Giraffe's had to make.
Problem with a two way breather converting to a one way breather is that (1) only one of the many new items (in tiny version, most likely) has no benefit and is a biological cost to make it. Having only one new sack with no air flow tube leading to it, even if full size needed, would be as useful as one fax machine only in the entire world.
You're still focused on air-sacs. As I have proven, one way breathing is not dependent on air-sacs and exists in tidal breathers (alligators being one example, monitor lizards being another).
(2) Adding in one air sack (or even a pair) inside a rigid rib cage, reduces the remaining volume for the two-way functional lungs. Thus not only is the new sack(s) totally useless and biologically expensive to make, but also they make the two-way respiratory system have less capacity. So when a herd of these creatures are running for their life trying to escape the carnivore chasing them - the one lagging behind with less capacity lungs is the one that gets eaten.
On the one hand, you're ignoring the fact that one-way breathing arose before airsacs, not after it. On the other hand you're ignoring the
EVIDENCE that we have that some dinosaurs - notably feathered theropods, including predators
had air sacs - something that you would know had you read the article in the OP.
EVOLUTION CAN NOT MAKE BINARY CHANGES as there is negative utility and added biological cost to the small incremental changes evolution can make.
Actually, it can, and it does.
Trippy concluded by asking:
"given that the one-way breathing structure is present in birds, if that you are contending evolution could not possibly have given rise to it, what would be your alternative explanation?"
That was exchemist, not me.
The real puzzle is how do we know that dinosaurs had two way flow? Perhaps like fish etc. they had one way flow so no problem for them to evolve into birds. If they had soft tissue gill like exit path for their breath it may have left no fossil record - I am just speculating - don't claim this to be the case.
You have got to be kidding me.
If you had read the damn article in the OP you would have seen that it explains that the evolutionary sequence that it posits is One way breathing -> Air sacs and that this was
in place by the time birds evolved from the feathered theropods. We have physical evidence that (for example) Tyranosaurs (or some of them did anyway) had airsacs. Again, this is something you would know had you bothered to read the article I linked to in the OP.
I raised guppies for a half year and as I recall they gulp air then expel it. (I wanted to get faster development of colored tails by selection of the females, which don't display their latent color - mate them with average color males then with more expensive highly colored males. Each female was keep in separate 1 gallon jar - I had an infinite free supply of them. I drop my project when I learned the female can store sperm for one mating and have even three later broods of live births form it.
Clearly that makes you an expert in both paleonotology and evolutionary biology.
I am not asserting that birds did not evolve from some subgroup of dinosaur like creatures - just that it is quite a difficult problem to show how they could have evolved from creatures that were "two way flow" breathers. So many analogue transition steps required, most of which would have negative benefit in addition to extra biological cost.
The feathered theropods that birds evolved from were one way breathers, not two way breathers, some of them even had air-sacs. Billy. Do you even know what an Archosaur is? I'll bet you think that Archosaurs are a specific kind of dinosaur. They're not.
Archosaur is the name of the clade that includes birds, dinosaurs, crocodillians, and pterosaurs, of which
Archosaurus and
Protorosaurus may have been the earliest members of (they were both late permian reptiles, sometimes classed as archosauroforms rather than archosaurs). The current hypothesis, as accepted by the mainstream, is that one way breathing evolved as long ago as 270 million years ago (late permian) in response to declining or low atmospheric oxygen levels. By the time of the Permian-Triassic boundary oxygen levels had dropped from arount 30% to around 10% and this is thought to have been the evolutionary pressure that gave rise to one way breathing in Archosaurs. This is supported or confirmed by the observation that Alligators and crocodiles have one way breathing because that suggests that it arose early in the archosaur timeline - before this split occured. The discovery of one way breathing among Therapsids is icing on the cake because either it evolved before the therapsid-archosaur split, or it evolved independently in therapsids.
I can see how there could be benefit for the alligator's ancestor to evolve an addition to its two-way breathing system, a more rapid exhale path for spending less exposed time on the surface when it needed a "gulp of fresh air" but the alligator still has two way flow thru the lungs, not one way thru the lungs flow like the birds do. That 2-way to 1-way change is a binary change.
No, it is not a binary change. The reason I say it is not a binary change is because one way plumbing works for two way breathing as well as one way breathing, and so it is possible to make small changes to the two way plumbing that are neither beneficial nor detrimental until one way breathing spontaneously arises - for example, see the alligator.