Why haven't whales evolved gills?

[Jupiter60]

Why haven't whales evolved gills?

 

[SteamKing]

Why should they?

 

[DiracPool]

Why haven't whales evolved gills?

Because they are mammals and they breath in a different way.

http://nmlc.org/2009/04/how-do-whales-breathe/

But with the terseness of you're inquiry I don't really expect this thread to last long. Hope you got something out of it...

 

[Bystander]

Why haven't whales evolved gills?

Whales evolved from gilled predecessors; should there be any advantage to devolving?

 

[SteamKing]

Whales evolved from gilled predecessors; should there be any advantage to devolving?

Do you have a reference for this?

Cetaceans are thought to have evolved from terrestrial mammals, and early whale ancestors are presently thought to be distantly related to modern-day hippos.

https://en.wikipedia.org/wiki/Evolution_of_cetaceans

As terrestrial mammals, there would have been no creatures with gills in their family tree.

 

[Bystander]

no creatures with gills in their family tree.

None? https://en.wikipedia.org/wiki/Vertebrate_Paleontology_and_Evolution

 

[ShayanJ]

I think the answer is crystal clear if we consider what evolution means.
As I understand it, evolution says that different traits may be introduced into a species by mutation which is an accidental process. Now this means that in the early stages of the introduction of a particular trait into the species, the species can be categorized w.r.t. having that trait or not or various degrees of that trait. Now if that trait is toward making the species less fit to its environment, its simply more probable that evolution of that species goes into a direction that that particular trait becomes less and less in the species. Note that its only a statistical process, species with that trait die sooner,reproduce less, that trait becomes less and less. That simple!
Getting back to the question. To our best knowledge, there is no whale that has gills. By the above reasoning, it simply means that having gills is incompatible with some other trait that whales have. I mean, it makes whales less fit to their environment if they have gills. That's the reason they don't have gills.
So the simple answer is what DiracPool said.

 

[Ygggdrasil]

Do you have a reference for this?

Cetaceans are thought to have evolved from terrestrial mammals, and early whale ancestors are presently thought to be distantly related to modern-day hippos.

https://en.wikipedia.org/wiki/Evolution_of_cetaceans

As terrestrial mammals, there would have been no creatures with gills in their family tree.

Mammals, like all other tetrapod species, evolved from fish. For example, during embryonic development, all vetebrate species show pharyngeal arches, gill like structures which develop into gills in fishes, but end up developing into the jaw and ears of mammals.

 

[SteamKing]

None? https://en.wikipedia.org/wiki/Vertebrate_Paleontology_and_Evolution

I'm talking about in relatively recent times geologically speaking.

I'm sure if you go back far enough, everything evolved from single-celled organisms, but that doesn't mean that humans necessarily will form spores and hibernate like bacteria do.

Dimetrodon is also thought to be distantly related to the ancestors of mammals, but I don't think any mammals will be evolving fancy sail structures along their spines.

https://en.wikipedia.org/wiki/Dimetrodon

Do you have any funny uncles who resemble this critter?

 

[Bystander]

https://en.wikipedia.org/wiki/Bison_latifrons#/media/File:Bison_latifrons_fossil_buffalo.jpg

 

[SteamKing]

https://en.wikipedia.org/wiki/Bison_latifrons#/media/File:Bison_latifrons_fossil_buffalo.jpg

There are similar structures on the vertebrae of many mammals, including humans:

http://anatomy-medicine.com/uploads/posts/2015-08/1440063932_anatomy-human-anatomy-human-body-spine-back-bones.jpg
​

This doesn't mean that human ancestors had sails popping out of their backs.

 

[Ygggdrasil]

Apparently, breathing air with lungs enables much higher rates of oxygen exchange than breathing water with gills, which allows whales and other marine mammals to have higher metabolic rates than fishes: https://www.newscientist.com/blogs/shortsharpscience/2009/08/why-whales-dont-have-gills.html

 

[Bystander]

should there be any advantage to devolving?

but that doesn't mean that humans necessarily will form spores and hibernate like bacteria do.

We're agreed.

Dimetrodon is also thought to be distantly related to the ancestors of mammals,

(Picture of one of my "funny cousins.")

This doesn't mean that human ancestors had sails popping out of their backs.

http://people.eku.edu/ritchisong/342notes2.htm
Actually, so long as vertebrae include a neural arch (spine) that is subject to whatever evolutionary pressures may favor elongation (or shortening), not only did my greatⁿ grandpappy (n = O(10⁸)) carry a sail, the great^m grandkids might also. Structures that have been highly modified or lost, gills, are not, according to my understanding of current evolutionary thought, likely to be recovered. It is possible, again to my current understanding, that other structures may be modified to handle special/exotic functions; "eyes/photoreceptors" were a popular example in my schooldays, and "No, I do not understand the mechanism for 'loss and recovery of vision' of cavefish in one or two generations." (I've heard discussions of "suppressed gene expression," and given up.)

Metabolic demands are obvious as pointed out by Ygggdrasil ;

Apparently, breathing air with lungs enables much higher rates of oxygen exchange than breathing water with gills, which allows whales and other marine mammals to have higher metabolic rates than fishes:

 

[cosmik debris]

A whale is warm blooded and a reasonable large creature which means its energy consumption is large. This in turn means that a large amount of oxygen is required to burn the fuel that it consumes. I'm guessing the amount of oxygen obtained using gills is just not enough to sustain the sea mammals, so evolving gills would be a backward step.

 

[DiracPool]

so evolving gills would be a backward step.

Yep, we're talking about reversing hundreds of millions of years of evolution. Seems to me much more efficient to float to the surface every now and then and expose your blow-hole to the oxygenated atmosphere with a relaxed attitude than to have to feverishly continue swimming through the water in order to get your oxygen fix.

You know relationships are a lot like this--they're a lot like sharks (which are fish), they have to keep moving or else they die.

 

[Jupiter60]

I would think that because whales are aquatic animals having gills would be an advantage. I guess that's not the case.

 

[DiracPool]

I would think that because whales are aquatic animals having gills would be an advantage.

Yeah, that's kind of the definition of a "naive assumption," aquatic animals=gills. But now you have 15 posts that educate you otherwise

 

[Alcathous]

A lot of what people are saying here is wrong or unsubstantiated. This is all quite difficult to figure out.
Just the mere fact that gills don't evolve doesn't mean having them, and paying their metabolic cost, wouldn't be an advantage. Also, having gills doesn't mean you can't have lungs.

Quite clearly marine mammals develop ways to deal with the problem of having to hold their breath. They just don't do so by evolving gills and they survive fine without them. Same for reptiles like the crocodile, which has evolved very little, meaning it has reached the optimum physiology, evolution can provide, for the niche it occupies.

Are gills not a convergent state of evolution? Can gills evolve into lungs but not lungs into gills? Has there not been enough time to evolve gills de novo? All these are fair questions without answers.

That there is 'no need' to have gills is only true to the extent that obviously whales don't go extinct without them. There is no 'need' in evolution, but that doesn't mean it wouldn't be an adventagous adaptation.
And evolution is happy to go either 'backwards' or 'forwards' depending on what labels we like to use; it is indifferent to this.

Also important to note is that some things just can't evolve no matter what the circumstance. This is why the parts biology uses are often so different from the parts we use to build our machines.

My main guess would be that because lungs already exist, it is hard to evolve something de novo that does the same thing, but differently. Absorbing tiny amounts of oxygen into the blood using skin spots that absorb O2 and act like the most basic of gills are likely to have almost no significance on the total O2 intake of the creature, as it already has lungs. And therefore no significant evolutionary advantage or selection for those genes. And even if it did, not sure if whales have been in the ocean for long enough to match the time it took the first time to evolve gills.

Therefore, adaptations are made to what already exists.

 

[DiracPool]

A lot of what people are saying here is wrong or unsubstantiated. This is all quite difficult to figure out.

It's not really difficult to figure out at all. Aquatic mammals are formerly land-based animals that returned to the sea and retained their lung breathing apparatus because it was sufficient for the job. If it wasn't, it would have evolved a different mechanism. Certainly, if selection demanded it, the aquatic mammals of today could "re-evolve" gills of some sort. I don't quite know what scenario might precipitate that, but that's a reasonable scenario. I don't think it would be a revival of our embrological gill arches, though, it would be a late phlogenetic trait "stacked" on top of everything else.

Can gills evolve into lungs but not lungs into gills?

Lungs would not likely evolve into gills. As you say, they would probably evolve "de novo" if that were to happen. The mammalian lung/respiratory system proper would probably atrophy and become vestigial.

 

[DiracPool]

Also, having gills doesn't mean you can't have lungs.

Evolution isn't 100% efficient by any means, but it is by necessity, parsimonious, and the odds are vanishingly small that it would retain two mutually distinct respiratory systems, especially in larger aquatic mammals.

 

[johnnymorales]

Why haven't whales evolved gills?

As long as whales are warm blooded, gills will be incompatible with their make up.

That they are warm blooded is why there has been no evolutionary changes that would make a whale able to breathe water despite the wholesale evolutionary makeover the ancestors of whales underwent to become modern whales.

Every single animal that has gills is cold blooded or mostly coldblooded (some sharks and Tuna and sea turtles) whose warmer body temps. lie in their interior, are far from the gills where they are less affected by the extreme cooling effects of breathing with gills, and restricted to certain organs and tissues (muscle, brain). Even then their ability to warm those specific regions is limited, and only as needed.

When you consider Whales have a body temperature similar to ours, and that many of them live in the high latitudes with water temps. around freezing, having gills with the amount of water necessary to keep them oxygenated would kill them via hypothermia without fundamental changes to its morphology. Even in much warmer waters the dying from hypothermia is a serious risk, because the water is much better at sucking the heat of something than much less dense air is. Humans for example can die of hypothermia in water as warm as 85 degrees or so if we are in long enough.

So if you think it makes sense for a whale to have gills, you need to figure out how a whale could keep a high body temperature. If you can't then you have the answer to your question.

Of course it's possible to imagine an extreme evolutionary tangent where somehow beginning with first being able to breath through their skin that something similar to gills could develop, but as long as whales are as big as they are, no such development would require so many changes to their current morphology that the creature that resulted would no longer be recognizable as a whale or even a mammal.

Also gills and lungs have nothing to do with each other anatomically. Lungs did not develop from gills.

Lungs began in terms of evolution as air sacs in fish that had become vascularized enabling them to extract oxygen from air. This ability became better and better as fish/amphibians moved into water with poor oxygen levels. Over 100s of millions of years those air sacs became the first very inefficient lungs.

It took millions of years more before a creature developed lungs so efficient they could dispense with gills. In the interim many had both lungs and gills, and some amphibians still have that set up.

So with fish evolution had fully functioning gills to breath with while a completely different part of their anatomy began the long process of evolving into lungs.

So if you still think whales should be able to develop gills you need to find some sort of starting point on their anatomy as it exists today, and think logically and rationally how that current anatomical feature might develop the ability to extract oxygen from water and then from there eventually turn into a gill like structure that could do what fishes do with their gills and do so without simply assuming that lungs would evolve into gills.

If you do this you'll realize it's practically impossible to imagine all the steps necessary to develop gill-like structures on a modern whale that wouldn't severely compromise its ability to survive as a whale.

Regardless, assuming someone could lay out all the hypothetical steps in a logical and rational manner for a whale to breathe water, without violating what we know regarding how evolution works, the wholesale changes to a whale's physiology would likely be so profound, that the resulting creature could not longer be called a whale or probably not even a mammal.

 

[DiracPool]

It took millions of years more before a creature developed lungs so efficient they could dispense with gills. In the interim many had both lungs and gills, and some amphibians still have that set up.

I like your post, and I kind of anticipated your quote above, especially in the transitory amphibians, which is why I revised my statement in my earlier post to ,"especially in larger aquatic mammals." However, I defend my position that evolution is parsimonious. But in the transitionary phases, if a trait or a redundancy does not negatively affect selection it does stand a chance of persisting, as in the amphibian cases you mentioned. Although, for the record, I have not researched this so I'm taking johnny's word here for the meantime.

 

[johnnymorales]

I like your post, and I kind of anticipated your quote above, especially in the transitory amphibians, which is why I revised my statement in my earlier post to ,"especially in larger aquatic mammals." However, I defend my position that evolution is parsimonious. But in the transitionary phases, if a trait or a redundancy does not negatively affect selection it does stand a chance of persisting, as in the amphibian cases you mentioned. Although, for the record, I have not researched this so I'm taking johnny's word here for the meantime.

Thanks. About the only thing I would take issue with is your use of the word parsimonious. I'm sure I get your point, but only by extrapolation.

 

[DiracPool]

About the only thing I would take issue with is your use of the word parsimonious

That's about the only thing you shouldn't take issue with. As sure as natural selection, evolution is built on parsimony. Do you disagree with this?

 

[johnnymorales]

That's about the only thing you shouldn't take issue with. As sure as natural selection, evolution is built on parsimony. Do you disagree with this?

The problem is I'm not sure YOU know EXACTLY what parsimony or parsimonious means, though it's clear you have a general idea. I DO know what it means, and how the word is supposed to be used. For that reason it is hard to just assume what you mean.

Thus I'm not absolutely certain what you mean when you use it to describe the process of evolution.

You're using the word in an incongruent context where what it measures doesn't exist.

You are using the word "parsimony Etc." as if it is a general use word with a meaning that can be applied in different contexts, and that's not right.

Parsimony is NOT a general use word.

The meaning of parsimony is tied to money and how you use it or your attitude about money.

In this context it's meaning is ambiguous. I can extrapolate from how it's used in that context to get an idea of what you mean, but have to assume a lot leaving much room for error.

Before I could answer your question as to what you think about evolution is right or wrong you should find a better word or phrase to describe what you think, because parsimony is definitely not it.

 

[Ygggdrasil]

That's about the only thing you shouldn't take issue with. As sure as natural selection, evolution is built on parsimony. Do you disagree with this?

If evolution is parsimonious, why do we have vestigial structures like a tailbone or an appendix? Why is about half of the human genome composed of repetitive sequences that are derived from viruses or mobile genetic elements? I get your general point and agree that an organism with both lungs and gills would likely vestigialize one of the organs if it used only one (it is much easier for random mutation to degrade unecessary function), but I'd disagree with the general statement that evolution is parsimonious.

Parsimony is NOT a general use word.

I also disagree that usage of the word parsimony is tied to money. The http://dictionary.reference.com/browse/law+of+parsimony, commonly referred to as https://en.wikipedia.org/wiki/Occam's_razor]Occam's[/PLAIN] razor or lex parsimoniae, is very often cited in many fields of science, including evolutionary biology.

 

[DiracPool]

If evolution is parsimonious, why do we have vestigial structures like a tailbone or an appendix? Why is about half of the human genome composed of repetitive sequences that are derived from viruses or mobile genetic elements?

Well, I'm using the term as a substitute perhaps for "extreme conservatism." It's pretty much the equivalent to the "least action" principle in physics. As I mentioned in an earlier post and as I'm sure you're aware, in evolution, if a vestigial structure doesn't have a deleterious effect on selection it's not necessary going to be phased out. If it takes more energy to remove the structure than it does just to ignore it, evolution is just going to ignore it. This goes the same for the genome. What you seem to be talking about is some form of an active vs. passive parsimony whereby the body sculpts itself to maximum efficiency. This is not how evolution works, so to say that evolution is parsimonious but to use vestigial structures as an argument to counter that assertion is think is wrong.

 

[Chronos]

My impression is whales were among a group of mammals who returned to the sea after evolving for life on land. Environmental factors probably favored their return to aquatic dwelling as a survival response.

 

[DiracPool]

Environmental factors probably favored their return to aquatic dwelling as a survival response.

What's your evidence for this? I see none. It doesn't have to be an environmental driver that pushed them back into the sea. Maybe they just tired of competing with the other land mammals and said I'm going to jump into the water and see what's down there.

 

[Alcathous]

Evolution cannot be generalised to be either parsimonious or 'extremely conservative'. Without selection pressure, change is inevitable.
And it is often postulated how evolution may be able to occur in bursts.

The best way to describe evolution is to describe the entire process, not to stick on it a few words.

It may actually be the case that one of the best pathways to evolve whales is to do it through land animals. Some adaptations whales have could not happen with only the selection pressures occur in the sea. Being warm-blooded and breathing air may be one among many.