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  • Usually, I'd start an episode of Eons by telling you about the discovery of some

  • strange fossil or setting the scene for a world-changing event like an ice age or an

  • extinction.

  • But today, I want to try something a little different.

  • Instead of thinking about a story, I want you to stop and think about the thing I'm

  • doing here - literally, that I'm standing here and telling you a story.

  • Because, the evolution of our ability to speak is its own epic saga - and it's worth pausing

  • to appreciate that.

  • It's taken several million years to get to this moment where I can tell you about

  • how it took several million years for us to get here.

  • And, yes, there are other animals alive today that communicate in sophisticated ways - like

  • whales, elephants, and crows, to name a few.

  • Still, our vocal abilities as a species are pretty unique.

  • They're part of what makes us human.

  • From the anatomy of one particular bone in our throats and the proportions of our vocal

  • tract, to the morphology of our ears, paleoanthropologists are piecing together the puzzle of when and

  • how this adaptation arose.

  • And while speech itself doesn't fossilize, the fossil record of our ancestors and relatives

  • can still give us important clues about the time when we first talked.

  • Now, this story could start between 400 and 360 million years ago, when the first ancient

  • tetrapods transitioned from life in the water to life on land, and evolved lungs and a movable

  • tongue.

  • Controlling both of these with precision is important for creating the many different

  • sounds that make up human speech.

  • Or it could start between about 8 and 6 million years ago, when our lineage - the hominins

  • - split off from the ancestors of our closest living relatives, chimpanzees and bonobos.

  • While there's no question that they can communicate with vocalizations, gestures,

  • and expressions, they can't speak like us - despite decades of effort to teach them

  • how.

  • And our earliest hominin relatives probably couldn't talk like us, either.

  • Because!

  • The first piece of fossil evidence that can be used to reconstruct hominin vocalization

  • comes from the skeleton of a juvenile Australopithecus afarensis dated to 3.3 million years ago.

  • This special bone is called the hyoid.

  • It's a U-shaped bone that sits in your neck just below the level of your jaw and it doesn't

  • connect to any other bone.

  • Instead, it's held in place by muscles and ligaments.

  • In humans, the hyoid is an important attachment point for the muscles of the tongue.

  • It does that in chimps, too.

  • But, in chimps - and in most other living apes - it also helps support structures called

  • laryngeal air sacs.

  • Now, we don't know exactly what these things do.

  • Some research has suggested that they might help make vocalizations louder and help primates

  • call for longer or more often without hyperventilating.

  • But they also seem to introduce new, lower resonances to vocalizations and reduce the

  • differences between higher-pitched sounds.

  • Both of which would make human speech sounds harder to understand.

  • And, here's the thing, the hyoid of Australopithecus afarensis looked more like those of chimps

  • and gorillas than it does like ours.

  • Which means that this hominin likely had air sacs attached to their hyoid.

  • So, her species probably couldn't speak like we do.

  • And that one hyoid is the only one we have from any species of australopithecine.

  • The hyoid is a small, fragile bone, so it's one of the least well-known bones in the hominin

  • fossil record.

  • In fact, the next oldest hyoids we've ever found come from a site that's almost three

  • million years younger.

  • In that span of time, the australopithecines disappeared, and our own genus, Homo, evolved,

  • with some populations even making their way out of Africa to Asia and Europe.

  • And a cave site in northern Spain called the Sima de los Huesos - or the Pit of Bones - is

  • where those next-oldest hyoids were found.

  • They've been dated to around 450,000 years old and belonged to members of the species

  • Homo heidelbergensis.

  • This species may be the common ancestor of Neandertals and our own species, Homo sapiens,

  • or it might just be a close relative of both.

  • And while both of the hyoids from this site are incomplete, what is preserved looks a

  • lot more like our hyoid than like the hyoid of Australopithecus afarensis or a chimp.

  • So, these hominins probably didn't have laryngeal air sacs.

  • But that doesn't necessarily mean they could talk like us - at least, not based on their

  • hyoid bones alone.

  • See, along with a lack of laryngeal air sacs, members of our species also have unique vocal

  • tract proportions.

  • You can split the vocal tract above the larynx, or voice box, into two basic parts.

  • The mouth makes up the horizontal part and the pharynx makes up the vertical part - the

  • bit between the mouth and the voice box.

  • In adult humans, these two parts are about the same length.

  • This allows us to make three of the different vowel sounds - a, i, and u - and to make them

  • sound really distinct from each other.

  • And almost all human languages have at least three vowels - and they tend to be these three.

  • This might be because they sound the most different from each other, so they're less

  • likely to be misheard.

  • But some anthropologists don't think that other hominins had these same proportions.

  • For example, researchers previously suggested that Neandertals had much shorter vertical

  • parts of their vocal tracts and longer horizontal parts.

  • Human infants and chimpanzees also have short vertical segments of their vocal tracts, and

  • can't make those distinct vowel sounds as a result.

  • But that fossil site in Spain can also give us clues about this piece of the puzzle.

  • Because, there's one individual with a nearly-complete skull and all seven neck vertebrae that researchers

  • have used to estimate the lengths of the two parts of the upper vocal tract.

  • They found that the horizontal part was actually only a little bit shorter than the vertical

  • part.

  • This makes the fossil's proportions more like those of a 10 year old human child than

  • an adult.

  • And 10 year olds can still make those same distinct vowel sounds, meaning this almost

  • half-a-million-year-old hominin probably would've been able to do it, too.

  • Some of our more recent relatives also seem to've had vocal tract proportions similar

  • to that individual.

  • When anthropologists reconstructed the vocal tract length of one adult Neandertal from

  • France dated to between 50,000 and 70,000 years ago, they found that the horizontal

  • section of his upper vocal tract was slightly shorter than the vertical section.

  • So, he, too, could probably make the full range of sounds found in human speech.

  • And there's more anatomical evidence for speech in Neandertals than just one reconstructed

  • vocal tract.

  • Bringing it back to the hyoid bone, we've found two from these extinct relatives of

  • ours.

  • One is from another cave site in Spain and dates to around 43,000 years ago.

  • It's incomplete, but was described as beingalmost indistinguishablefrom a modern

  • human hyoid.

  • The second is a little older, dating to around 60,000 years ago, and comes from a site in

  • Israel called Kebara Cave.

  • It also looks a lot like our hyoid bones.

  • The scientists who worked on this bone even CT-scanned it to see if its internal structure

  • was a match for a human hyoid.

  • See, bone can actually change or remodel its microscopic architecture over time, based

  • on how it's being used.

  • So if a Neandertal was using the muscles and ligaments that attach to its hyoid the same

  • way we do, CT scans of our hyoids should look similar, too.

  • And they did!

  • Which means that both the outside and the inside of the hyoid of this Neandertal suggest

  • that he was capable of making human-like speech sounds.

  • But!

  • Being able to make human-like speech sounds is only half the story - the other half is

  • being able to hear them.

  • While paleoanthropologists haven't found very many fossil hyoids, they have found a

  • lot of skulls.

  • These allow them to study things like the size and shape of the ear canals - and sometimes

  • even the tiny bones of the ear themselves - because they're contained within the temporal

  • bones of the skull.

  • And by comparing the fossils to the anatomy of living primates and humans, they can model

  • the hearing ranges of our extinct relatives.

  • Early hominins, like Australopithecus africanus and Paranthropus robustus, have some features

  • of their ears that look more like ours than like a chimpanzee.

  • For example, they have a slightly shorter and wider passage leading from the outside

  • of the skull to the membrane of the eardrum.

  • And they have a malleus - one of the bones of the middle ear - that looks human-like.

  • But the other two bones of the middle ear - the incus and stapes - are more chimp-like

  • in size and shape.

  • And when their hearing abilities are modeled, they're not quite like ours or like those

  • of a chimp.

  • These early hominins seem to have been more sensitive to mid-range frequencies than modern

  • humans or chimps are.

  • More human-like ear anatomy and hearing abilities seem to originate in our genus, Homo.

  • Homo erectus fossils from Asia have some human-like features, and the hominins from Sima de los

  • Huesos and the Neandertals are even more similar in ear anatomy to Homo sapiens.

  • The same hearing model used for the early hominins predicts that the later members of

  • our genus probably had hearing abilities like ours.

  • They lost a little bit of the mid-range frequency sensitivity seen in early hominins, but expanded

  • their range of maximum sensitivity to include higher frequencies.

  • It's been suggested that greater sensitivity to those higher frequencies is important for

  • hearing consonants, especially t, k, f, and s.

  • And the use of consonants is a key feature that distinguishes human language from most

  • animal communication.

  • These changes in ear anatomy and hearing ability go along with the changes in the hyoid bone

  • over time - early hominins were more similar to our closest living relatives and the members

  • of our genus Homo are more similar to us.

  • And by the time we get to the Sima de los Huesos hominins and the Neandertals, we seem

  • to have all the anatomy in place for distinct vowel and consonant sounds -- which is pretty

  • incredible!

  • Now, we don't know if this means these extinct relatives had language.

  • This is still a big topic of debate and we don't have enough evidence to say either

  • way.

  • It might just come down to how we define language.

  • But what we can say is that there's no anatomical reason they couldn't make and hear human-like

  • speech sounds.

  • And we know the Neandertals were capable of very human-like behavior, like caring for

  • injured members of their groups and using objects for personal ornamentation.

  • So maybe they were storytellers, too.

  • As the only hominins left, it's up to us to piece together the puzzle of our ancestors'

  • speech abilitiesand use our own to tell this evolutionary story.

  • Hey if you wanna learn more about all the ways in which Neandertals were similar to

  • us...as well as what happened to them, be sure to check out our episode, “When We

  • Met Other Human Species”.

  • Now I have to say this month's Eontologists are : Sean Dennis, Jake Hart, Annie & Eric

  • Higgins, John Davison Ng, and Patrick Seifert!

  • By becoming an Eonite at patreon.com/eons you'll get fun perks including submitting

  • a joke for us to read like this one...

  • from my friend Matty Dahman.

  • Why did the T Rex need a nap?

  • Because he was wiped out.

  • I need a nap after this script!

  • Thanks Matty for submitting your joke.

  • And as always thank you for joining me in the Konstantin Haase studio.

  • Subscribe at youtube.com/eons for more adventures in deep time.

Usually, I'd start an episode of Eons by telling you about the discovery of some

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B1 US vocal human tract bone homo speech

When We First Talked

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    joey joey posted on 2021/05/03
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