Why can humans swim? (layman question)

[Constantinos]

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?

 

[Ken Natton]

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.

 

[Ryan_m_b]

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.

 

[russ_watters]

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?

Water pressure is irrelevant: the human body is not rigid, therefore it does not need/attempt to resist the pressure.

 

[Constantinos]

I see. So we can swim because of other traits we evolved for different selective forces in an indirect manner I suppose.

Water pressure is irrelevant: the human body is not rigid, therefore it does not need/attempt to resist the pressure.

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!

 

[SteamKing]

There's quite a few lakes and rivers in Africa. It's not all desert, you know.

 

[mishrashubham]

There's quite a few lakes and rivers in Africa. It's not all desert, you know.

http://en.wikipedia.org/wiki/Geography_of_Africa#Hydrology

At OP;

some links that might interest you...
http://en.wikipedia.org/wiki/Mammalian_diving_reflex
http://www.djur.cob.lu.se/Dyk/summary.html

 

[nitsuj]

Two thoughts on this one. Firstly, we evolved from fish. .

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.

 

[Ken Natton]

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.

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.

 

[nitsuj]

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.

I would guess the strongest link between humans swimming and evolution is a fear.

 

[aroc91]

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.

 

[russ_watters]

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.

Sure, it would contract, but why would that lead to discomfort if it contracts uniformly?

So the pressure has to be relevant, isn't it so?

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.

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.

There is nothing to adapt to.

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!

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.

 

[Constantinos]

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!

 

[Constantinos]

http://en.wikipedia.org/wiki/Geography_of_Africa#Hydrology

At OP;

some links that might interest you...
http://en.wikipedia.org/wiki/Mammalian_diving_reflex
http://www.djur.cob.lu.se/Dyk/summary.html

Thanks for the links!

And of course, I know that Africa has a lot of water and it's not all desert, but that alone does not mean that animals inhabiting it would be able to swim.

 

[Gliese123]

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.

 

[moejoe15]

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.

 

[Evo]

A cute video.



https://www.youtube.com/watch?v=9ObDgBLFo9w

 

[Ryan_m_b]

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.

 

[Ken Natton]

We swim because we want to. There isn't much that can't swim... You don't need evolution to swim and we didn't 'evolve' to swim.

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.

 

[mishrashubham]

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.

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.

 

[thegreenlaser]

I would tend toward believing that it's a learned skill. There's lots of people who drown because they can't swim.

 

[adaptation]

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.

Who says monkeys can't swim? Many people say apes cannot based on their distribution of body fat. If this is the case, it doesn't matter how smart they are.

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.

Swimming is not like riding a bike or driving a car. It is more like hunting (for other animals like the big cats). There is a learned component and an instinctual one. Humans (along with many other mammals) have a diving reflex. This is a very well documented reflex. The key word is reflex.

I would tend toward believing that it's a learned skill. There's lots of people who drown because they can't swim.

Like I said above, only part of it is learned. Am I the only one who knows that human babies can swim? They hold their breath and open their eyes when they are submerged. They also display the dive reflex.

Much of our evolution contributes to our ability to swim: voluntary breath control, dive reflex, generally streamlined shape, distribution of fat, etc.

 

[Evo]

Who says monkeys can't swim? Many people say apes cannot based on their distribution of body fat. If this is the case, it doesn't matter how smart they are.



Swimming is not like riding a bike or driving a car. It is more like hunting (for other animals like the big cats). There is a learned component and an instinctual one. Humans (along with many other mammals) have a diving reflex. This is a very well documented reflex. The key word is reflex.



Like I said above, only part of it is learned. Am I the only one who knows that human babies can swim? They hold their breath and open their eyes when they are submerged. They also display the dive reflex.

Much of our evolution contributes to our ability to swim: voluntary breath control, dive reflex, generally streamlined shape, distribution of fat, etc.

Pigs swimming in the caribbean. No diving.

http://www.youtube.com/watch?v=aQSCCDM5zh8&feature=related

https://www.youtube.com/watch?v=aQSCCDM5zh8&feature=related

 

[Chronos]

I was under the impression primates were the only critters lacking instinctive ability to swim.

 

[Evo]

I was under the impression primates were the only critters lacking instinctive ability to swim.

Nope, lots of primates swim.



https://www.youtube.com/watch?v=sAcB1YqZgTY

http://www.youtube.com/watch?v=-ngQ699_U2I&feature=related

https://www.youtube.com/watch?v=-ngQ699_U2I&feature=related

http://www.youtube.com/watch?v=9fPZFHOK3VU&feature=related

https://www.youtube.com/watch?v=9fPZFHOK3VU&feature=related

 

[mishrashubham]

Swimming is not like riding a bike or driving a car. It is more like hunting (for other animals like the big cats). There is a learned component and an instinctual one. Humans (along with many other mammals) have a diving reflex. This is a very well documented reflex. The key word is reflex.Like I said above, only part of it is learned. Am I the only one who knows that human babies can swim? They hold their breath and open their eyes when they are submerged. They also display the dive reflex.

Much of our evolution contributes to our ability to swim: voluntary breath control, dive reflex, generally streamlined shape, distribution of fat, etc.

Swimming is one thing, adapting to stay underwater longer is another. I am well aware of the "Mammalian Diving Reflex". However, it is an adaptation that gives drowning people a chance to survive. It does not ensure survival, nor does it give people the ability to swim. Swimming is pretty complex behaviour and much of it needs to be learned. In addition, diving is different from swimming. You are right in saying that instinct does play a role and I never denied that.

 

[ZealScience]

But bears, dogs, even some pigs could swim. I think if trained, lots of species could swim, so it's rather a skill sometimes.

 

[adaptation]

Human babies can swim. Generally if an animal can do something without learning how to do it, we call that an instinct. Instincts come from evolution. So does it not stand to reason that swimming, an instinct, evolved in humans?

Baby swimming:
http://psycnet.apa.org/psycinfo/1940-01122-001
http://books.google.com/books?hl=en...dNwHFrjAuFyYWfx3ok#v=onepage&q=reflex&f=false

You can google hundreds of baby swim programs in your area, thousands of videos of babies swimming, and millions of anecdotes on the subject.

This does not mean that humans naturally swim well. Tigers do not naturally hunt well. If a tiger is hungry, it will attempt to hunt. If a human is in the water, it will attempt to swim. This is instinct. In both cases, however, if the animal in question has not honed its skill in hunting/swimming, the end result is likely death.

You can even liken it to the "fight of flight" response. Just because your body tells you to attack or flee, does not mean you will be successful with either.

 

[Ryan_m_b]

wow, way to put it in a bad context. Are any of your black swimming friends Olympians for their swimming skill? Thats what miniradman had mentioned.

miniradman hadn't even remotely suggested that black people cannot swim, you assumed it.

Should have replied to miniradman that it is merely a cultural difference, if the statement is accurate at all. I would guess Inuit are not particularly good swimmers compared say, Hawaiians. I would also guess that is a cultural difference, not a genetic one.

This thread already clearly ruled out the specific role of evolution with regard to humans swimming and concluded that learned skill is the biggest factor in swimming ability.

I was referring to these parts of the post

I'm not being racist or anything but I present a question to everyone. How many dark skinned (I think you know what I mean) people win the olympics for swimming? I can't name any. But studies has shown that males with a heavier muscle density tend to sink rather than swim. Now if we go back to the pre-swimming era, there primitive humans hight quite a high muscle density... this is why many people from Africa have trouble swimming than people in Europe, it's all down to muscle density.

The asking for studies was in reference to the proposed explanation for a proposed observation. The reference to black swimmer friends was to put forward the point that there is no barrier to athletic black swimmers yet miniradman was suggesting that there is a biological reason as opposed to a social one.

 

[Evo]

I'll offer this article which quite accurately explains why certain groups have more exposure to different activities.

http://www.guardian.co.uk/commentisfree/2008/aug/25/race.olympics2008

 

[mishrashubham]

Human babies can swim. Generally if an animal can do something without learning how to do it, we call that an instinct. Instincts come from evolution. So does it not stand to reason that swimming, an instinct, evolved in humans?

Baby swimming:
http://psycnet.apa.org/psycinfo/1940-01122-001
http://books.google.com/books?hl=en...dNwHFrjAuFyYWfx3ok#v=onepage&q=reflex&f=false

Your second reference specifically mentions reflexes. Like I have said, the existence of reflexes doesn't mean a natural affinity for swimming. The fact that we shiver in response to cold doesn't imply that our natural habitat is supposed to be far north.

Your first reference tells that voluntary swimming movements are only observed in babies more than two years old. Prior to that, all we have are reflex actions. However I would still like to have a look at the entire paper.

You can google hundreds of baby swim programs in your area, thousands of videos of babies swimming, and millions of anecdotes on the subject.

I do not deny that babies can swim. What I find hard to believe is babies swimming without any training at all.

This does not mean that humans naturally swim well...If a human is in the water, it will attempt to swim. This is instinct. In both cases, however, if the animal in question has not honed its skill in hunting/swimming, the end result is likely death.

Precisely my point.

 

[Evo]

Human babies cannot swim, it is something called a "dive reflex". This "dive reflex" is also responsible for infant deaths.

Until around 6 months, babies placed in water tummy-side down will move their arms and legs in a swimming motion. When the swimming reflex and the dive reflex are both engaged, a baby can look like a natural swimmer.

Cautions about babies in water

"These reflexes don't mean the baby can swim, though," says Wagener. What's more, they don't protect a baby from drowning. (In addition to the risk of drowning, it's dangerous for an infant to swallow large amounts of pool water.)

http://www.babycenter.com/404_is-it...born-with-the-ability-to-swim-and_10313062.bc

Sudden infant death triggered by dive reflex

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1770553/

 

[miniradman]

hmmm... to be perfectly honest, I think there is more than just ONE answer to this question. I think it has just as much to do with biology and sociology... I don't think there is just ONE answer