Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Why can humans swim? (layman question)

  1. Aug 9, 2011 #1
    I have a very limited knowledge of biology (whatever learned from high school and popularizations). But I don't understand how could humans evolve the ability to be able to swim and dive in water. For all I know, humans evolved only on land in Africa and the ability to swim should have been a very rare necessity. That should also hold true for our most immediate evolutionary ancestors. Even more mysterious is the fact that the human skin and outside cavities can stop water from entering the body even under a great water pressure. I could understand it should evolve to be resistant to rain, but how come most humans can dive in depths many meters deep? How could the skin and cavities evolve to stop so much water?
     
  2. jcsd
  3. Aug 9, 2011 #2
    Two thoughts on this one. Firstly, we evolved from fish. Perhaps some of our ability in water is vestigial rather than specifically evolved.

    Also, for a significant period of time, our ancestors lived a nomadic existence, following the great herd migrations out of necessity. That involved a lot of river crossing. I suspect that those river crossings were quite a strong selective force.
     
  4. Aug 9, 2011 #3

    Ryan_m_b

    User Avatar

    Staff: Mentor

    Remember that humans are not the only animals to swim, many other land mammals do to. Swimming is a complicated behaviour so it's unlikely humans evolved to swim. More likely we evolved some traits that then also allowed our ancestral species to swim. The skin is as it is because it must act as a barrier for the body against the outside world, part of the protection for infection is waterproofing.
     
  5. Aug 9, 2011 #4

    russ_watters

    User Avatar

    Staff: Mentor

    Water pressure is irrelevant: the human body is not rigid, therefore it does not need/attempt to resist the pressure.
     
  6. Aug 10, 2011 #5
    I see. So we can swim because of other traits we evolved for different selective forces in an indirect manner I suppose.

    I'm not sure I understand this. Pressure is P = dF/dA the force on a unit of area. The total force on a unit of area on the human skin should be the force from within the human body (which is constant in respect to the depth one is) and the force from the water (which rises with the depth). So at some depth the total force should be directed into the human body and the bigger the depth, the bigger the force, so at some point the body would have to contract(not sure if this is the right word) leading to discomfort or worse. So the pressure has to be relevant, isn't it so? Well yes the human body is not rigid, but bending under pressure is not good either. So the question was how did the human body evolve to accept such pressure. I'd guess though that the pressure 10 or 20 meters deep doesn't change significantly in comparison to the pressure on the surface so we can do alright!
     
  7. Aug 10, 2011 #6

    SteamKing

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    There's quite a few lakes and rivers in Africa. It's not all desert, you know.
     
  8. Aug 10, 2011 #7
    Last edited by a moderator: May 5, 2017
  9. Aug 10, 2011 #8
    So did my cat, and the mice it eats, and and and...... they hate water and sure they would drown. I think for Giraffes it's physicaly impossible for them to swim.

    However that second point regarding river crossings, very good. I too think that would have been a strong selective force.

    Evolved to swim? Yea, and I evolved to be able to drink from a straw.
     
  10. Aug 10, 2011 #9

    Cats don’t particularly like water but they absolutely can swim if they have to. In any case, the point about our distant ancestry is more subtle than that, and my point stands, there are some aspects of our current morphology that are vestigial from our aquatic ancestry, something that is most apparent in the early stages of our embryonic development.

    But, as I had thought to say to Constantinos, my post really was just musings, it is very clear that Ryan’s posts are far more authoritative than mine. As far as Constaninos’ original question was answerable, Ryan answered it.
     
  11. Aug 10, 2011 #10
    I would guess the strongest link between humans swimming and evolution is a fear.
     
  12. Aug 10, 2011 #11
    Keep in mind that the ability to keep water out of our bodies is merely the inverse of the more important function of keeping water IN out bodies.

    Edit: keeping out infection is also a key part, as ryan mentioned.
     
  13. Aug 10, 2011 #12

    russ_watters

    User Avatar

    Staff: Mentor

    Sure, it would contract, but why would that lead to discomfort if it contracts uniformly?
    Not really, no. The problems of swimming at a large depth all have to do with the effects the pressure has on our chemistry, not the force itself.

    The world record for scuba is 330m, which is the equivalent of about 30 atmospheres of pressure.
    There is nothing to adapt to.
    Well, recreational divers often do 30m and that's 3 atmospheres of pressure. It's quite a lot if you consider the force of that extra pressure. Your body probably has a surface area of around a square meter, so that's an extra 300,000N of force. If it mattered, it would matter.
     
  14. Aug 13, 2011 #13
    Ok people, Thanks for the replies, I think I have a good picture now!

    Ah I see, yes I believe I understand. Your post was pretty informative. Thanks!
     
  15. Aug 13, 2011 #14
    Last edited by a moderator: May 5, 2017
  16. Aug 14, 2011 #15
    Well, yes we're able to swim but it's perhaps not our biggest expertise. Humans are able to adapt to different environment and learn theoretical and practical how to exercise. There are good swimmers and there are good runners, human anatomy is more flexible to different tasks, compared to other species.
     
  17. Aug 15, 2011 #16
    We swim because we want to. There isn't much that can't swim. I can't think of many species that can't. If something is capable of motion on land then it is probably capable of using the same techniques in water. Snakes use the same motion to swim as move on land. Birds didn't evolve to swim yet some can go under the water and use the same techniques as flying to 'fly' under water (and I don't mean Penguins). You don't need evolution to swim and we didn't 'evolve' to swim. If a monkey was as smart as us it would probably use a similar technique as we do to swim, they aren't that physically different.
     
  18. Aug 15, 2011 #17

    Evo

    User Avatar

    Staff: Mentor

    A cute video.



    https://www.youtube.com/watch?v=9ObDgBLFo9w
     
    Last edited by a moderator: Sep 25, 2014
  19. Aug 15, 2011 #18

    Ryan_m_b

    User Avatar

    Staff: Mentor

    D'aw cute video. On the subject of evolving to swim I'm surprised that it slipped my mind not to mention Cetaceans earlier, specifically how they evolved from terrestrial to aquatic creatures.
     
  20. Aug 15, 2011 #19

    Yes, on the face of it, my initial response to the question was essentially to feel dismissive about the notion that we evolved to swim rather than that swimming was just a skill we happened to learn along the way. But I thought that an interesting point did emerge. The OP did ask a question about the impermeable nature of our skin and Ryan pointed out that impermeable wasn’t so much a question of waterproofing as of infection proofing. Waterproof was just a property that happened to come along with infection proof. That, I thought, was a telling point.
     
  21. Aug 15, 2011 #20
    Right. We need not have specifically evolved to swim. It could be just another skill that we developed akin to riding a bicycle or driving a car.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Why can humans swim? (layman question)
  1. Why can animals swim? (Replies: 8)

Loading...