1st tetrapods breathed through their ears
Mystery Of Mammalian Ears Solved
A 30-year scientific debate over how specialized cells in the inner ear
amplify sound in mammals appears to have been settled more in favor of
bouncing cell bodies rather than vibrating, hair-like cilia, according to
investigators at St. Jude Children's Research Hospital.
The finding could explain why dogs, cats, humans and other mammals have such
sensitive hearing and the ability to discriminate among frequencies. The
work also highlights the importance of basic hearing research in studies
into the causes of deafness.
"Our discovery helps explain the mechanics of hearing and what might be
going wrong in some forms of deafness," said Jian Zuo, Ph.D., the paper's
senior author and associate member of the St. Jude Department of
Developmental Neurobiology. "There are a variety of causes for hearing loss,
including side effects of chemotherapy for cancer. One strength of St. Jude
is that researchers have the ability to ask some very basic questions about
how the body works, and then use those answers to solve medical problems in
The long-standing argument centers around outer hair cells, which are
rod-shaped cells that respond to sound waves. Located in the fluid-filled
part of the inner ear called the cochlea, these outer hair cells sport tufts
of hair-like cilia that project into the fluid. The presence of outer hair
cells makes mammalian hearing more than 100 times better than it would be if
the cells were absent.
As sound waves race into the inner ear at hundreds of miles per hour, their
energy--although dissipated by the cochlear fluid--generates waves in the
fluid, somewhat like the tiny waves made by a pebble thrown into a pond.
This energy causes the hair cell cilia in both mammals and non-mammals to
swing back and forth quickly in a steady rhythm.
In mammals, the rod-shaped body of the outer hair cell contracts and then
vibrates in response to the sound waves, amplifying the sound. In a previous
study, Zuo and his colleagues showed that a protein called prestin is the
motor in mammalian outer hair cells triggers this contraction. And that is
where the debate begins.
While both mammals and non-mammals have cilia on their outer hair cells,
only mammalian outer hair cells have prestin, which drives this cellular
contraction, or somatic motility. The contraction pulls the tufts of cilia
downward, which maximizes the force of their vibration. In mammals, both the
cilia and the cell itself vibrate. Thus far the question has been whether
the cilia are the main engine of sound amplification in both mammals and
One group of scientists believes that somatic motility in mammalian outer
hair cells is simply a way to change the height of the cilia in the fluid to
maximize the force with which the cilia oscillate. That, in turn, would
amplify the sound. An opposing group of scientists maintains that although
the vibration of the outer hair cell body itself--somatic motility--does
maximize the vibration of the cilia, the cell body works independently of
its cilia. That is, vibration of the mammalian cell dominates the work of
amplifying sound in mammals.
"If somatic motility is the dominant force for amplifying sound in mammals,
this would mean that prestin is the reason mammals amplify sound so
efficiently," Zuo said.
In the current study, Zuo and his team conducted a complex series of studies
that showed in mammals that the role of somatic mobility driven by prestin
is not simply to modify the response of the outer hair cells' cilia to
incoming sound waves in the cochlea fluid. Instead, somatic motility itself
appears to dominate the amplification process in the mammalian cochlea,
while the cilia dominate amplification in non-mammals.
Zuo's team took advantage of a previously discovered mutated form of prestin
that does not make the outer hair cells contract in response to incoming
sound waves as normal prestin does. Instead, the mutated form of prestin
makes the cell extend itself when it vibrates.
The St. Jude researchers reasoned that if altering the position of the cilia
in the fluid changes the ability of the cilia to amplify sound, then hearing
should be affected when the mutant prestin made the cell extend itself.
Therefore, the team developed a line of genetically modified mice that
carried only mutant prestin in their outer hair cells. The researchers then
tested the animals' responses to sound.
Results of the studies showed no alteration in hearing, which suggested that
it did not matter whether the outer hair cells contracted or extended
itself, that is, raised or lowered the cilia. There was no effect on
amplification. The researchers concluded that somatic motility was not
simply a way to make cilia do their job better; rather, there is no
connection between the hair cell contractions and how the cilia do their
job. Instead, somatic motility, generated by prestin, is the key to the
superior hearing of mammals.
A report on this work appears in the advanced online issue of "Proceedings
of the National Academy of Science."
Other authors of this study include Jiangang Gao, Xudong Wu and Manish Patel
(St. Jude); Xiang Wang, Shuping Jia and David He (Creighton University,
Omaha, Neb.); Sal Aguinaga, Kristin Huynh, Keiji Matsuda, Jing Zheng,
MaryAnn Cheatham and Peter Dallos (Northwestern University, Evanston, Ill.).
[From DB or AAT? dive down past the spherical harmony section if you like]
Regarding hearing, humming and spherical/planar/scalar harmony
Semi-circular ear canals in mammals, primates
The primate semicircular canal system and locomotion
Fred Spoor, Theodore Garland Jr, Gail Krovitz, Timothy M Ryan, Mary T Silcox
& Alan Walker 2007
The semicircular canal system of vertebrates helps coordinate body
movements, including stabilization of gaze during locomotion. Quantitative
phylogenetically informed analysis of the radius of curvature of the three
semicircular canals in 91 extant and recently extinct primate species and
119 other mammalian taxa provide support for the hypothesis that canal size
varies in relation to the jerkiness of head motion during locomotion.
Primate and other mammalian species studied here that are agile and have
fast, jerky locomotion have significantly larger canals relative to body
mass than those that move more cautiously.
From the discussion:
... The strong relationship between SCC.size & locomotor agility is clearly
evident in a variety of primate groups. The leaping tarsiers & galagos have
large canals relative to their body size, whereas the slow quadrupedal
lorises, although of similar body size, lie on the lower end of the
distribution with relatively small canals. At larger body masses, this
relationship also holds. The acrobatic brachiating gibbons have rel.large
canals for their body size, compared with the great apes. The sloth lemurs
& koala lemurs have small canals for their body size, and Palaeopropithecus
in particular has very small canals to match its reconstructed extremely
slow locomotion. (Some or all of these subfossil large Madagascan fossils
may have been aquarboreal. --MV) In some cases, canal size does not seem
to match expectations based on the locomotor behavioral classification. This
could occur when a small, unrepresentative sample falls toward the margins
of a species¹ morphological range of variation, especially when combined
with a less secure estimate of body mass. It may also be that locomotor
behavior was misclassified because certain aspects critical to the
perception of angular rather than linear motion were not recognized. A
possible example is Ateles geoffroyi, which is classified as medium in
agility, but its rather large canals fit well with its acrobatic behavior.
Importantly, the 3 canals do not necessarily express locomotor behavior in
equal measure, because this may depend on the planes of head motion
involved. For example, during hominin evolution only the anterior &
posterior canals enlarge with the emergence of modern-human-like bipedal
locomotion (2). In contrast, tarsiers & galagos on the one hand, and lorises
on the other are most distinct in lateral canal size. Likewise, the small
lateral canal of Alouatta seniculus is consistent with its less agile
behavior. However, its anterior canal appears unexpectedly large, possibly
the consequence of spatial constraints of the subarcuate fossa (24), which
opens into the endocranial cavity through the arc of the anterior canal, and
houses a lobule of the cerebellum. In all, the species that most strikingly
seem to contrast with the overall canalagility correlation are the 4
callitrichids. These are classified as agile, but their anterior & lateral
canals fall between the middle & lower end of the canal size distribution.
It is unclear why this is, and more work will need to be done to understand
the factors underlying this exceptional morphology. In nearly all cases, the
phylogenetic GLS models employing some type of branch length transformation
outperformed both the star phylogeny (conventional regression) and the GLS
method by using untransformed divergence times gathered from the literature.
Of the 3 branch length transformations used, Grafen¹s & Pagel¹s typically
performed best. The addition of well dated extinct species throughout our
phylogenetic tree will result in more accurate reconstructions of the
ancestral nodes, which in turn may then allow a better reconstruction of
the evolution of characters. Nevertheless, as was found here, transformed
trees may still perform better than those based on divergence times. This
may be for a variety of reasons, including the presence of unavoidable
measurement error in the estimates of species¹ mean BM and canal radii (25).
The similarity of results between the conventional and the phylogenetic
regression models indicates that the SCC system holds a very strong
functional signal related to head motion & locomotor agility. Such an
apparently robust functional relationship across primates & other mammals
suggests that adjusting arc size, and thus endolymph circuit length,
constitutes a prime adaptive mechanism of how the canal system is tuned to
the kinematic characteristics of different locomotor repertoires. This
finding will contribute to a more fundamental understanding of the
biomechanics of the canal system. On a more practical level, it confirms the
potential utility of the SCCs for the reconstruction of behavior from fossil
... 86 Ma for Primates/Scandentia-Dermoptera (Springer et al.).
... 77 Ma for Strepsi/Haplorhine split ...
The base of Strepsirrhines at 69 Ma (Yoder & Yang)
the base of Lorisiformes at 55 Ma,
the base of Lemuriformes at 62.7
... Afr./As.lorises was set at 42 Ma
... Galagoides/Galago-Otolemur clade was set to 30 Ma
The base of the Haplorhines was set at 55 Ma (Ross et al.) based on the
presence of Tarsius eocaenus at 45 Ma.
... platy/catarrhine is placed at 43.6 Ma (Eizirik et al.).
The base of the platyrrhine radiation is set at 25 Ma based on the initial
appearance of platyrrhines in the fossil record during the early Mio. The
presence in the Miocene of fossils purported to belong to modern clades
suggests a rapid radiation of known clades after 25 mya.
... cercopith/hominoid split was placed at 34.7 Ma (Yoder & Yang), which is
similar to other estimates (15).
The phylogeny of hylobatids was based on Roos & Geissmann, & the divergence
dates were arbitrary following the 15 Ma split with hominids (sensu
The divergence dates within hominids were based on Stauffer et al.
Information & reasonable speculation on mammal and human hearing and its relationship to ancestral human foraging.
Me: Both the cuboctahedron (VE) and the icosahedron have equidistant vertexial nodes. An icosahedral sphere can be divided into 31 equilateral great circles [circumscribed icosahedral geodesic sphere] associated with 12 vertexial nodes, the human body has 31 spinal nerve pairs associated with 12 cranial nerves, and an octave can be split equally into 31 pleasing tones and as well the 12 notes of the major scale.
Per Rybo: Archimedes 4-fold asymmetrical cubo-octahedral (VE)-- is defined by 4 Great Circles) and has 8 equilateral triangles composed of 24 chords (3 x 8 = 24)
The VE also can be conceptually spun (or centrally split) to create 25 primary Great Circles.
The 25 Great Circle's will subdivide the VE's spherical surface.
Plato's 5-fold symmetrical Icosahedron can be conceptually spun (or centrally split) to have 31 primary Great Circles. 10 of the Icosahedrons 31 Great Circles will function to define five different 4-fold, 4 Great Circles of the VE.
Please see this site on spinal & cranial nerves (click on pic):
DM: "Lots of people believe that the human menstrual cycle is somehow coupled to the moon."
Me: Yes, for good reason I'm sure. The vast majority of life on Earth dances to the solar-lunar-tidal cycle dance.
Fishermen and hunters tend to follow the solunar cycles when crepuscularly active, whether or not they are actually at the tideline. Our ancestors were no doubt far more in tune with the lunar tidal flows than modern humans in urban areas are. While the women bled safely either at seashores or in caves (not moving around in the woods or the bush), the men would hunt and fish without distractions.
DM: "They overlook two very important things: firstly, the 29-day duration of the menstrual cycle is an average of a range of several days, and secondly, the human menstrual cycle is just that -- human".
Me: Apes also have similar estrus cycles, hylobats (gibbons, siamangs) (and possibly orangutans?) are quite close to humans cycles also, while chimps and gorillas have been away from the tidal effect due to being more inland, so their cycle has changed, becoming more terrestrial (monkey-like).
DM: "Rats have a cycle of 11 days. Chimpanzees have one that is a bit longer than the human one. Why should of all mammals we be coupled to the moon?"
Me: Both sun and moon. Our bodies' extra-cellular fluids have a salinity level of 9ppt, in between the Baltic sea and the Black sea, approximately estuarine, with pH level similar to seawater, we "are" the sea. However I can't answer your question without mentioning that our ancestors spent much time at the tidal shores foraging. If you picture our ancestors just swinging around and then dashing about on the splendid savannah with the little kitty cats, then I don't think you would be interested in my seashore speculations.
DM: "I think you have likewise merely found a coincidence. In keeping with this, not even all mammals have the same number of vertebrae and therefore spinal nerve pairs".
Me: The numbers 31 and 12 pop up together in "unexpected coincidental" correlations. If humans are the least derived physically, most derived mentally, from the primitive mammalian condition, then 12 and 31 might be of great significance. Need more data though.
DM: "I forgot... 31 pleasing tones? Can it get more subjective than that?"
Me: Please see this article:
DM: "Not just among humans. Not all ears are human. Bird ears, for example, are quite different from mammal ears -- their high pitch limit is below the mammalian one (though above the one we humans actually reach), but they can discriminate more tones within the same frequency range. Pleasing or not, they'd vehemently disagree with "31"."
Me: I'd assume that most insectivorous birds would have excellent pitch determination. Cave swifts use non-target echolocation. I don't know the jaw-ear configuration in birds, dino, pterasaurs, marine reptiles, would be interesting comparisons.
(DM above is David M. who left comments in "What Thumb?" post, the unedited dialog is found at Tetrapod Zoology Science Blog, Dinosaur feathers II)
Dinosaur-mammal info: click here
195ma "shrew" Hadrocodium ancestor of placentals? mammal ears
125ma "newt-like?" Yanoconodon near-mammal ears semi-aquatic?
125ma "opossum" Eomaia
81ma - 55ma? "mouse-lemur-like" Oldest LCA primates
42ma Texas coast lagoon primates
Ancient human divers: jaws, hearing, vocalizing, ear exostosis