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Dorsal fin helps to stabilize the creature in water much like rocket with fins, how could such a cunning apex marine predator be missing a dorsal fin? Also how do they compensate for it during high speed chase?

Note: merfolk enjoys drive hunting which demands sudden burst of speed as well as making sharp turns.

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closed as primarily opinion-based by MichaelK, L.Dutch, Ash, Frostfyre, sphennings Oct 11 '17 at 12:51

Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise. If this question can be reworded to fit the rules in the help center, please edit the question.

  • $\begingroup$ Some species of whales don't have dorsal fins either. How can you explain that? $\endgroup$ – a4android Oct 11 '17 at 4:10
  • $\begingroup$ @a4android: and how fast do they swim? $\endgroup$ – user6760 Oct 11 '17 at 4:20
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    $\begingroup$ I am sorry but this question is silly, and displays a huge lack of understanding how evolution works. Traits do not pop into existence because they would be useful to future generations. That is not at all how evolution works. If evolution had done what is best for the future of a species, then humans would not have had a genetic deficiency that makes us susceptible to Scurvy from lack of vitamin C instead of creating it in our bodies like so many other species, nor would we have a retina that is backwards. This sort of thing does is not a problem that needs solving. It is already solved. $\endgroup$ – MichaelK Oct 11 '17 at 6:21
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    $\begingroup$ @user6760 Then you need to read up on evolution a little bit before you ask a question about evolution. Dogs have become a separate family from wolves though selective breeding by humans, yes. $\endgroup$ – MichaelK Oct 11 '17 at 6:53
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    $\begingroup$ @user6760 That comment was a complete Non Sequitur. $\endgroup$ – MichaelK Oct 11 '17 at 13:23
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Hands

Dorsal fins largely function to stabilize against rolling. A Merfolk's hands can accomplish that function and much more. Being on wrist joints, they can pivot to allow the creature whatever degree of control they wish. Additionally, as they're attached to the useful appendages called arms, they can also be used for propulsion and other tasks as well.

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  • $\begingroup$ to achieve streamline in water I thought it would be best for merfolk to keep their arms by the sides or do the superman pose... except they don't clench their fists. $\endgroup$ – user6760 Oct 11 '17 at 3:49
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    $\begingroup$ @user6760 If you're going for speed, yes. A remarkable amount of control can be achieved via small hand movements, especially if there's webbing between the fingers. Just like rockets, where the control surfaces are tiny compared to the actual vehicle. $\endgroup$ – Andon Oct 11 '17 at 4:01
  • $\begingroup$ @user6760 might I recommend checking out people who swim with monofins and mermaid tails? They have their hands out and to a point. Like the A in YMCA, but with the palms downward and not together. $\endgroup$ – Lot-Of-Malarkey Oct 11 '17 at 5:12
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An issue I thought of was placement. A dolphin's dorsal fin is kinda in the space behind where the rib cage ends. On humans that would be the small of the back. If you ever watch someone try to do a dolphin kick or swim with a monofin, they need to have a good sense of flow throughout the body. Putting a dorsal fin there may make the back stiffer and impede that.

A dolphin is very hydrodynamically shaped and the dorsal fin is basically the highest part of its body. I don't know if a human would be optimally shaped for using a dorsal fin, unless maybe it was really large. I still think that would be detrimental since that could also increase water resistance.

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  • $\begingroup$ You may want to clarify/re-word your answer. I initially thought you were answering on how a human-shaped creature would have a dorsal fin, not how a human-shaped creature is bad for a dorsal fin. $\endgroup$ – Andon Oct 11 '17 at 5:31
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    $\begingroup$ @Andon Thats fair. I've elaborated on the first part as to why that placement isn't very good. $\endgroup$ – Lot-Of-Malarkey Oct 11 '17 at 13:29

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