How Animals Hear: Crash Course Zoology #7 - Free Educational videos for Students in K-12 | Lumos Learning

How Animals Hear: Crash Course Zoology #7 - Free Educational videos for Students in k-12


How Animals Hear: Crash Course Zoology #7 - By CrashCourse



Transcript
00:0-1 our environments are filled with information . Just think of
00:03 all the stuff that comes at us each day ,
00:06 like light and sound and even objects . It's almost
00:10 overwhelming when you think about it . But animals are
00:13 pretty resourceful figuring out how to take it all in
00:16 and weed out what's not important . In fact ,
00:19 we and other animals often put our whole bodies into
00:23 it like heads , knees , legs , abdomens and
00:27 10 I wings . They're all body parts of animals
00:31 used to learn about their environment just through hearing .
00:34 So let's talk about what an ear even is ,
00:37 how it has evolved , how they work . And
00:40 some of the cool ways animals have tweaked their ears
00:43 to work for their lifestyle . Perk up whatever you
00:46 use for hearing because I'm going to be sending vibrations
00:50 your way for the next 10 ish minutes . I'm
00:53 Ray Wynne Grant and this is crash course zoology ,
01:06 like all senses , hearing involves collecting information from the
01:10 environment and processing that information into signals that the brain
01:14 can understand specifically Hearing is the ability to interpret your
01:19 environment using vibrations that move through air , water or
01:23 even solid objects . Hearing organs like ears are just
01:27 one way animals can interpret the sounds in their environment
01:31 . And while we vertebrates trace all our ears to
01:34 one ancestor , invertebrates have independently evolved ears over and
01:39 over again over 24 times in just insects alone .
01:43 So like vision , hearing is a spectrum . Some
01:47 animals have very sensitive hearing and some don't here at
01:50 all . For those of us who is hearing organs
01:53 are ears . Ears have to minimum requirements to work
01:57 a sensor that turns vibrations into nerve signals and the
02:01 brain power to interpret those signals into different sound qualities
02:05 . Most animals that here , even if they don't
02:08 have what we call ears , rely on special hair
02:12 cells which are named for the little hair like Tufts
02:14 that come off of them called stereo cilia . Sound
02:18 vibrations cause the stereo cilia to sway , which leads
02:22 to the hair cell sending signals to nearby neurons that
02:25 relay information to the brain . Our hair cells are
02:29 in our internal ear , the part that does the
02:32 actual hearing that sits behind a thin membrane or eardrum
02:36 . The outside part called the pinna works like a
02:38 satellite dish to amplify and direct sound into our internal
02:42 ear . Pinna are very much a mammal thing .
02:46 Some species pinna even move to track sounds . Many
02:50 other vertebrates , like most reptiles and amphibians don't have
02:53 pinna . Their external ears are simple openings and some
02:58 animals like fish , have no external ears at all
03:01 , hearing only the sounds that reach their internal ear
03:04 after moving through their body . But some animals have
03:07 gone a different route . Frogs and toads usually have
03:10 internal ears , but there are over 200 species that
03:14 have reduced or even lost many internal ear parts .
03:18 These mostly fearless toads , can still hear some sounds
03:22 like a crock by feeling vibrations which might be all
03:27 they need to chat with their friends and detect predators
03:30 . Like I said before . Unlike we learned about
03:32 vision hearing and the organs we used to do it
03:35 come in a whole spectrum and also like eyes .
03:39 We can compare hearing organs based on what they can
03:42 do . Most of our understanding of hearing is about
03:45 how big ish animals handle . Far field sounds .
03:49 Far field sounds are sounds that have traveled far enough
03:52 away from the thing that makes the noise that they
03:55 act like a typical wave very close to the sound
03:58 source . The sound waves push on the air or
04:00 water particles around them , so you get weird auditory
04:04 effects as the particles bump into each other . Some
04:07 invertebrates use this kind of sound called near field sound
04:10 to communicate with each other and detect predators . Though
04:13 the two aren't mutually exclusive , some arthropods can also
04:17 make . And here far field sounds . We can
04:20 also compare different animals . Hearing ranges which is the
04:24 range of frequencies that an animal can detect frequencies are
04:28 the number of times particles of a material vibrate in
04:31 a certain time period . When a sound wave passes
04:34 through it , one cycle of vibration in one second
04:37 is called , one hurts us . Humans have a
04:40 decent hearing range of about 20 to 20,000 hertz .
04:45 We experience frequency as pitch or the loneliness or highness
04:50 of a sound which we can also compare . But
04:52 many animals can hear sounds under 20 hertz which we
04:55 call infrasound or above 20,000 hertz . Which we call
05:00 ultrasound . Like wax mouse can hear 300,000 hertz sounds
05:05 squeaky er than any bat of course like best eyes
05:09 or best brain . Best ears or hearing isn't really
05:13 an award . We can give out . Animal hearing
05:15 has evolved to pick up on the type range and
05:18 pitch of sounds that they encounter and need to respond
05:21 to in their environment . And as we'll see how
05:24 animals here has changed a lot in the hundreds of
05:28 millions of years they've been around but as for who
05:32 can hear . Well it depends on what you call
05:36 hearing and what you call an ear for us .
05:39 Humans hearing usually means sounds moving in air but there
05:43 are other ways vibrations can travel . As of 2021
05:47 we know a lot of arthropods keep their ears to
05:50 the ground literally by sensing vibrations as they move through
05:54 the earth and that's pretty much hearing even though they
05:57 don't have ears that look anything like ours . Other
06:01 invertebrates like jellyfish are trickier . They definitely have sensors
06:05 that could detect waves . But since I live underwater
06:09 , we can't tell if they're responding to sound waves
06:12 or like normal water waves . So for a long
06:16 time sociologists thought that only vertebrates could hear airborne sounds
06:21 , since invertebrates don't have ears like ours , But
06:24 that got thrown out with a series of meticulously designed
06:28 experiments by high school teacher Charles . H . Turner
06:31 . Let's go to the thought bubble . It's standard
06:34 these days to account for extra factors that might influence
06:37 research results . But in 1907 , when Turner published
06:41 his first hearing study , his experimental design was revolutionary
06:45 . First he insulated ant nests from ground vibrations with
06:50 cotton batting and carefully controlled the lighting in the room
06:54 . Then he used a dog whistle , organ pipes
06:57 and his own voice from different distances . And he
07:00 repeated the experiment many times , and even used heat
07:04 filters to keep the animals from sensing the warmth of
07:07 the lights . With all those controls , the ants
07:10 scuttled away when he made noise , which Turner interpreted
07:13 as evidence that his aunt's could here . Turner then
07:17 investigated hearing in moths using a dog whistle again ,
07:20 Taking precautions at the animals weren't just responding to the
07:23 site of the whistle or air movement . According to
07:26 his results . Moths could here , too , he
07:29 reported in 1914 that the moths responded to high but
07:33 not low frequency sounds , and mused that moths might
07:38 still be able to hear the lower sounds , but
07:41 only responded to sounds that were important , like the
07:44 high pitched whistle that sounded a bit like a bat
07:47 . So he tested this idea by jostling the mobs
07:50 when he made a low frequency sound . Soon the
07:54 moths learned that low pitched noises were dangerous and fluttered
07:57 their wings in response to just the low frequency sound
08:01 . So not only did he prove moths could hear
08:03 sound even if they didn't respond to them , but
08:06 also that moths could learn thanks . Thought bubble Turner
08:11 was a brilliant and productive scientist . He was the
08:14 first african american to earn a PhD from the University
08:17 of Chicago , but was excluded from professorships at white
08:21 universities . Even today . Many black entomologists faced similar
08:25 barriers , But Turner's work with Moss was one of
08:28 the earliest examples of conditioning and insects and foundational to
08:33 the work of many later scientists studying insect learning and
08:36 behavior . In addition to Turner's moths and ants since
08:40 1907 , we've learned that lots of insects and at
08:43 least some Iraq needs , like spiders can hear airborne
08:47 sounds . Thanks to the work of many other scientists
08:50 , Many insects even use hairs tuned to particular frequencies
08:55 , sort of like stereo cilia . Other insects have
08:58 a TIM panel organ in their legs , wings ,
09:00 abdomen and other places that vibrates and ends up sending
09:05 signals to the brain . Invertebrate hearing evolved dozens of
09:09 times in lots of different ways , which makes sense
09:13 since there are 34 ish file of invertebrates out there
09:16 . But vertebrate style hearing only evolved once in a
09:20 fish ancestor , which was passed on to all tetrapods
09:25 or animals with four limbs , like mammals , birds
09:28 , reptiles and amphibians . We know that because even
09:31 though vertebrate years vary widely , they always use the
09:35 same hair , cell centered mechanism based on fossil evidence
09:39 . We think that the earliest vertebrate years were entirely
09:43 internal like fish years are today and evolved over 500
09:48 million years ago , which is probably why fish hear
09:51 low frequency sounds best . They passed through the body
09:55 more easily than high frequency sounds . Then , as
09:58 vertebrates moved onto land roughly 400 million years ago ,
10:02 things got more complicated . Like if you've ever been
10:06 swimming at a public pool , you might have noticed
10:08 how much quieter everything seems underwater . That's because a
10:12 lot of airborne sounds bounce off the water surface instead
10:16 of traveling through the water . This same thing happened
10:19 to those early land vertebrates but only had internal years
10:24 . The sounds in the air bounced off their denser
10:26 ear tissue and didn't reach the hair cells , so
10:29 they probably only heard very loud , low frequency sounds
10:33 that is until tim panic , middle ears or ears
10:37 with an ear drum and obstacles evolved which they did
10:40 independently . At least three times these external ears allowed
10:46 sounds in the air to come into direct contact with
10:49 the inner ear without traveling through the skull and other
10:52 tissues . This made a huge difference in how well
10:56 land animals could hear ears spread across meadows . Oh
10:59 , a because just like eyes , they're super useful
11:03 vertebrates probably first evolved hearing to gather more information about
11:08 their environment and avoid hazards . Whereas insects evolved hearing
11:12 so they could keep an ear out for vertebrate predators
11:15 . Except for those noisy cicadas , They just wanted
11:18 a way to talk to each other . Some of
11:19 our biggest leaps and understanding how animals interact with sound
11:23 . All happened very recently and I'm sure we'll learn
11:27 even more interesting stuff soon . Next episode will get
11:31 into the really old and weird ways animals sense their
11:34 environment . Thanks for watching this episode of crash course
11:38 ideology , which was produced by complexity in partnership with
11:41 PBS and Nature . It's shot on the team Sandoval
11:44 Pierre stage and made with the help of all of
11:46 these nice people . If you'd like to help keep
11:49 crash course free for everyone forever , you can join
11:51 our community on patreon . Yeah .
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