How did dolphins and sharks both evolve fins?

The accumulation of small heritable changes within populations over time.

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Re: How did dolphins and sharks both evolve fins?

#21  Postby BlackBart » Dec 07, 2020 7:28 am

And where did the Narwhal get his pointy stick from eh? Take that Atheists!
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Re: How did dolphins and sharks both evolve fins?

#22  Postby The_Piper » Dec 07, 2020 10:43 pm

Belugas are spooky. :whine:
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Re: How did dolphins and sharks both evolve fins?

#23  Postby felltoearth » Dec 08, 2020 12:27 am

Oh look, it’s Roofi... erm, Raffi!




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Re: How did dolphins and sharks both evolve fins?

#24  Postby Blackadder » Dec 10, 2020 3:12 pm

BlackBart wrote:And where did the Narwhal get his pointy stick from eh? Take that Atheists!


It's the Rod of God.
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Re: How did dolphins and sharks both evolve fins?

#25  Postby Spearthrower » Dec 14, 2020 8:51 pm

5380Zzaj wrote:The theory of evolution has an enormous amount of confirmatory evidence and I do not question its scientific usefulness. But the explanations offered thus far still leave puzzling questions. The concept of "conversion" (that significantly divergent genetic lines can develop similar structures due to similar environmental conditions) is, of course, a description, not an explanation.


That's quite the thread-necro... what was it? 10 years? :)

I find your last sentence very confusing. It is a description, but necessarily contains its explanation. The explanation is evolution. It's what evolution does; adapt morphology to environmental conditions. Evolution accounts in explanatory terms for the shark's fin. Evolution accounts in explanatory terms for the dolphin's fin.

Evolution doesn't account directly in explanatory terms for the apparent similarity between the shark and the dolphin's fin because evolution can't 'see' them both together like that comparatively. Rather, there's a shared environment with the same constraints, the species exhibit similar behavioral patterns (chase and kill predation), and as such both shark and dolphin bodies experience the same physical forces and demands and evolve to adapt to that shared condition. Perhaps there's other ways that stabilization could occur, perhaps there are even superior anatomical structures... but perhaps it's like many things with evolution; that something which initially offers only a tiny benefit gets added to consecutively and honed statistically to arrive at a smaller pool of possible morphologies each step either offering minor benefits over prior morphology, or offering some kind of entirely new benefit not available with prior morphology, or not offering any reproductive benefit whatsoever and just the product of statistical shuffling.

I feel like the kind of 'explanation' you might be looking for is perhaps unrealistic - that you'd want to see a series of consecutive 'whys' - this happened because of this, all the way back in an unbroken chain to shark and dolphin ancestors lacking fins. Perhaps I am wrong in this, but it's not clear to me what form you'd imagine 'explanatory' to take if evolution doesn't already satisfy that question.


5380Zzaj wrote:So how did the dorsal fin of of the cetaceans evolve? Some genes during evolution do become inactive as a particular feature may no longer be useful. Five toes of early horses became useless as the horse developed hooves but the five toes gene still exists in a dormant state and could be reenacted at a future time. But the dorsal fin gene is not to be found at any time in the evolution of mammals. It was suggested that the gene might have been carried dormant from mammal's fish ancestry. Possibly but not plausible. Fish fins are boney structures and found on various parts of the body. Dorsal fins are fleshy and found on only one area. Furthermore, the other cetacean appendages developed from leg and tail bone structures already highly developed in prior mammals. The dorsal fin is totally unique. It is not boney and is located on the gut segment of the body that never had any appendage genes during the whole of mammal evolution.


I think these are good questions, although not entirely accurate throughout. However, as you've identified: fish and dolphin fins only appear similar, but in reality they are not. The convergence is mostly that they both possess something there rather than that there's a lot of similarity to those traits. You talk about 'the' dorsal fin gene, but how can it be the same gene if you say it is, on the one hand, coding for a bony structure, and on the other coding for a non-bony structure? The answer is two-fold: that they possess the same anatomical shape doesn't infer that the same gene is responsible, and secondly, if you want to talk about genes one to one with traits, then you are obliged to look at the environment the gene is acting within because it is only coding for proteins - how those proteins then behave is dependent on the cellular chemical environment unique to the animal hosting that gene.

Finally, what does it mean to say that the dorsal fin is "entirely unique" with respect to a trait of a particular animal? We could identify hundreds of such traits which are 'unique' in that sense, including the one you've cited. Pit vipers have 'unique' infra-red sensing glands, woodpeckers have a 'unique' bone in their tongue, cats are 'unique' with respect to the number of bones they have in their tails as a fraction of their total bones... and so on, and so on. While we can say each is 'unique', the dolphin is not unique in having unique traits. How did they get these traits... well, even if you don't find it satisfactory, evolution by selection and in some cases simple drift accounts in explanatory terms for it.



5380Zzaj wrote:Although the Orca's fin might help in stabilizing motion, It is difficult to understand how a small "accidental lump" could in anyway be beneficial to survival. A small lump provides no stabilization benefit, thus no survival benefit and, therefore, no natural selection could promote its further development.


I don't agree. Clearly in this case, a small lump is better than none because that's how stabilization works; optimal stabilization is ideal, but in the absence of that, some stabilization is better than none. If you took a smooth board of wood on the ocean and tried to surf, then compared that with a board of wood with even a tiny little block underneath like a rudder, you'd immediately notice the difference. The first would be very hard to even stand up on as the board would keep sliding away - even a small lump begins to offer some directing resistance to water flow that helps stabilize the weight distribution for you on the board which in turn allows you to achieve better or more consistent forward motion and turns. Your capability to surf on different boards isn't seen by evolution of course, but an aquatic animal whose entire life consists of moving through a medium that could potentially be manipulated by some minor morphological diversity offers a great opportunity for selective adaptation to take effect.


5380Zzaj wrote:I have not come across any answer to this question. I'm still looking. But please don't just say that "evolution explains it".


But why not? Evolution DOES explain it definitionally respecting what the word 'explanation' means. You can't hope for a more comprehensive explanation.

Evolution does explain how a trait which offers some benefit might be positively selected through iterative heritable reproduction coupled with mutation and/or naturally occurring variation. My sense though is that you want to understand why it occurred in the first instance rather than seeking to understand how it happened mechanically over time. It's more 'why' do they both have these anatomical shapes, or 'why' did the dolphin grow anatomy unlike its ancestors because the how is relatively straight forward and clear.

However, while WHY questions are vital, I believe, to inspire queries about the world around us, we can't answer WHY questions to anyone's satisfaction. Why didn't dolphins evolve frog-like legs with webbed toes instead? I don't know. I don't think anyone knows or could know. I don't believe even if we could model and simulate every possible component of the environment and factors that we could even then answer a WHY question satisfactorily; we'd just keep adding more and more details to our HOW account of the event. In blunt honesty, the final answer we're ever going to have to an ultimate WHY question is "because it did". That's not expressly a limitation of science, of reason, or of logic... it's basically an inherent component of its own linguistic and cognitive constraint.
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Re: How did dolphins and sharks both evolve fins?

#26  Postby felltoearth » Dec 14, 2020 9:15 pm

oh I,
I wish you could swim
Like dolphins
Like dolphins can swim...




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Re: How did dolphins and sharks both evolve fins?

#27  Postby Hermit » Dec 16, 2020 12:35 am

Spearthrower wrote:Clearly in this case, a small lump is better than none because that's how stabilization works; optimal stabilization is ideal, but in the absence of that, some stabilization is better than none. If you took a smooth board of wood on the ocean and tried to surf, then compared that with a board of wood with even a tiny little block underneath like a rudder, you'd immediately notice the difference. The first would be very hard to even stand up on as the board would keep sliding away - even a small lump begins to offer some directing resistance to water flow that helps stabilize the weight distribution for you on the board which in turn allows you to achieve better or more consistent forward motion and turns.

No surfboards had fins until Blake Edwards attached a "bulge" to his in 1938. Initially it was a piece of aluminium. Later it was replaced by a piece of wood, which made it easier to reshape.

Image

Surfboard fins have evolved in various - sometimes wondrous - ways ever since. By the early 1950s most boards had "skegs", a D-shaped piece of wood sandwiched between layers of fibreglass. Later in the decade the skegs were made entirely of fibreglass.

Image

In the 1960s came "high aspect" fins like the one favoured by George Greenough.

Image

Nowadays the fins are smaller, but there are more of them on each board.

Here's a short, illustrated account for those who are interested.
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Re: How did dolphins and sharks both evolve fins?

#28  Postby Spearthrower » Dec 16, 2020 5:40 am

Exactly - my analogy to surfing drew from direct experience. Not long after I'd learned to surf (in Byron Bay, of course!) I went out with a cousin in NSW and on the way to the beach one of his boards had the fiberglass fin smashed clean off his old board. We still took it out for a laugh, but it was comically difficult to even stand on the board let alone control it.
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Re: How did dolphins and sharks both evolve fins?

#29  Postby Cito di Pense » Dec 16, 2020 7:46 am

Lateral (anti-roll) stability in fluid dynamics has been worked out mathematically. Aeronautical engineers needed to put vertical stabilizers on airplanes in order to reduce the workload of pilots, but learned from nature. It's not just something that humans figured out. Lateral stability predated humans, because it's physics, not theology.

5380Zzaj wrote:
I have not come across any answer to this question. I'm still looking. But please don't just say that "evolution explains it".


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Re: How did dolphins and sharks both evolve fins?

#30  Postby Hermit » Dec 16, 2020 9:02 am

Spearthrower wrote:Exactly - my analogy to surfing drew from direct experience. Not long after I'd learned to surf (in Byron Bay, of course!) I went out with a cousin in NSW and on the way to the beach one of his boards had the fiberglass fin smashed clean off his old board. We still took it out for a laugh, but it was comically difficult to even stand on the board let alone control it.

Finless surfing is not that difficult. I started to learn how to surf on Midge Farrelly's Coolites. They were basically finless blobs of styrofoam. No glass, so it never took long to snap them, which became a significant financial drain for this schoolboy. Later on I bought a Brothers Neilsen surfboard. It was cheap because although it had a fin box there was no fin to go with it and I could not afford to buy one. So I surfed it sans fin for about a month until I had enough fibreglass scraps to lay one up and shape it myself.

If you are interested in surfing boards without fins I can recommend the movie "Musica Surfica". It features a whole bunch of waxheads on finless boards. Also, Richard Tognetti, who was the artistic director of the Australian Chamber Orchestra at the time the movie was made, and is (in my opinion) a world class violinist.

Here's the trailer:

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Re: How did dolphins and sharks both evolve fins?

#31  Postby Spearthrower » Dec 16, 2020 10:38 am

Finless surfing is not that difficult.


It's certainly more difficult than with a fin - at least it was for me. It felt like the board following the line of least resistance resulted in it rotating away from the direction of travel which was not something I'd experienced at all previously while learning with a finned board.

Edit: actually, thinking back to it and the experience that day, I remember that the only real success I had on a finless board was when I was crouched quite low to the water - you had to keep your centre of weight much lower else the board went whizzing off. Translating that back to anatomy, that's an awful lot to change morphologically comparative to adding a little hump for stability.
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Re: How did dolphins and sharks both evolve fins?

#32  Postby Hermit » Dec 16, 2020 12:02 pm

Spearthrower wrote:
Finless surfing is not that difficult.

It's certainly more difficult than with a fin

Yes, it is, and I definitely prefer boards with fins to ones without any. Still, keeping in mind the limitations finless boards impose, they are not that difficult to ride. Your experience that "it was comically difficult to even stand on the board let alone control it" is not shared by everyone. Watch this bloke for instance.

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Re: How did dolphins and sharks both evolve fins?

#33  Postby Spearthrower » Dec 16, 2020 12:45 pm

Hermit wrote:Your experience that "it was comically difficult to even stand on the board let alone control it" is not shared by everyone. Watch this bloke for instance.


I'm not really sure that comparing someone who'd spent a couple of weeks learning to someone who's spent their life doing it as a professional is really very illuminating.

To wit: does the fact that a professional surfer can board well without fins mean that it was not comically difficult for me to even stand on the board let alone control it?
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Re: How did dolphins and sharks both evolve fins?

#34  Postby Hermit » Dec 16, 2020 1:05 pm

Spearthrower wrote:does the fact that a professional surfer can board well without fins mean that it was not comically difficult for me to even stand on the board let alone control it?

No. And that was not what I argued, so kindly abandon that strawman. It's pretty weird since you actually quoted what i did write. To wit: "Your experience that "it was comically difficult to even stand on the board let alone control it" is not shared by everyone."

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Re: How did dolphins and sharks both evolve fins?

#35  Postby Spearthrower » Dec 16, 2020 1:10 pm

A direct question is not a strawman, Hermit.

Such an idea is equally absurd as if I'd replied to you saying: I didn't say it was comically difficult for EVERYONE to stand on the board let alone control it - so stop strawmanning me!

Obviously, it's because you weren't trying to strawman what I said, you were just making a poorly conceived argument which I then explained was flawed.

Why are you playing silly games here anyway Hermit? I don't know what gets into you sometimes - it's like you want to make a point that's not being contested or even relevant, then start getting snitty about it. Weird behavior.

And as for the last line - frankly, that's juvenile trolling and I expect better of you.
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Re: How did dolphins and sharks both evolve fins?

#36  Postby The_Piper » Dec 16, 2020 2:23 pm

I bought a kid's boogie board at Virginia Beach and yada yada yada, it resulted in an ER visit and 3 weeks of light-duty. :dopey:
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Re: How did dolphins and sharks both evolve fins?

#37  Postby Spearthrower » Dec 16, 2020 3:00 pm

The_Piper wrote:I bought a kid's boogie board at Virginia Beach and yada yada yada, it resulted in an ER visit and 3 weeks of light-duty. :dopey:


What the fuck did you do? Crash into a tanker? :grin:
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Re: How did dolphins and sharks both evolve fins?

#38  Postby The_Piper » Dec 16, 2020 3:35 pm

Spearthrower wrote:
The_Piper wrote:I bought a kid's boogie board at Virginia Beach and yada yada yada, it resulted in an ER visit and 3 weeks of light-duty. :dopey:


What the fuck did you do? Crash into a tanker? :grin:

I was laying on it in shallow water, and a wave caught the front of it just right, sending it nosediving into the sand and my rib absorbed the force of the fall, banging into the edge of the board. I had the wind knocked out of me, but luckily still had the presence of mind to not draw a breath until the wave crashed over me (I landed flat on my back underwater). I staggered along the shore looking for my friend, who laughed when he saw me. :lol:
It only bruised a rib or two but remained tender for a while.
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Re: How did dolphins and sharks both evolve fins?

#39  Postby felltoearth » Dec 16, 2020 5:36 pm

Oof!


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Re: How did dolphins and sharks both evolve fins?

#40  Postby Spearthrower » Dec 16, 2020 6:41 pm

The_Piper wrote:I was laying on it in shallow water, and a wave caught the front of it just right, sending it nosediving into the sand and my rib absorbed the force of the fall, banging into the edge of the board. I had the wind knocked out of me, but luckily still had the presence of mind to not draw a breath until the wave crashed over me (I landed flat on my back underwater). I staggered along the shore looking for my friend, who laughed when he saw me. :lol:
It only bruised a rib or two but remained tender for a while.


That power of water - shit can get real unexpectedly fast. I had a friend who actually lost her eye a few days after she started surfing as she fell over the front of the board and it whacked her square in the socket.

My worst experience was in Sri Lanka where an otherwise quite gentle looking wave seemed to grab me by the scruff of the neck and bury my face in the sea floor for what felt like a minute. It was a very strange and cautionary experience - that's the last time I really relaxed while in anything other than a few inches of water.
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