Wikipedia and the scientific community
Mouth and lips
Humans have everted lips with exposed (red) mucosa, and a relatively much smaller mouth opening than other primates and than most tetrapods [9, 10]. This means that our biting possibilities are restricted, and this is also reflected by the possession of smaller front teeth, especially smaller canines. In general, carnivores have very large mouth openings with much larger canines than herbivores.
The human oral cavity is relatively much shorter than that of chimpanzees and the front teeth are less protruding (absence of oral prognathism) and are implanted vertically. The canines are incisor-like (more spatulated and not lengthened) and all the teeth are of nearly equal height so that the tooth row forms a closed dental arcade shaped like a parabola or semi-circle without diastemata (i.e., gaps where the opposing canines fit) [11-14].
The strength of the human masticatory musculature is weakened by inactivation of the gene for myosin heavy chain 16 (MYH16), a muscular protein that, at least in primates, is found only in the temporalis and masseter muscles of the jaw [15, 16]. Non-human apes, on the other hand, as most insecti-, carni- and omnivorous terrestrial mammals, have prognathic muzzles and rectangular dental arcades with long, strong canines and large diastemata, protruding front teeth, and two parallel rows of cheek teeth (premolars and molars). Their hard palate (the bony part of the palate) is not highly vaulted, but rather long and flat (horizontal), with transverse ridges (rugae palatinae) that probably have the function of fixing the food so that it can be chewed without slipping away [11, 12]. Whereas the tongue of apes is long and flat, humans have a round, thick, globular, bulbous tongue that is very versatile and can be shaped to fit tightly at any place against the arched and smooth (ridge-poor) palate and the parabolic tooth row [11-14, 17, 18]. At least some of the differences of the human oral cavity, when compared to other apes, might be explained as adaptations to eating foods that can be sucked into the mouth and swallowed with minimal chewing (e.g., soft fruits, grubs, eggs and/or slippery seafoods).
184 Fifty Years after Alister Hardy Waterside Hypotheses of Human Evolution
Humans lack prognathism. They retain (possibly through neoteny) the short, flat face of the suckling infant, which may be an adaptive feature in order to more easily consume (slippery) seafoods later in life. The consumption of seafood might help explain the round tongue perfectly fitting in the smooth (rugae-poor) and vaulted palate, so that the tongue can obstruct the oral cavity at all possible places (e.g., dental, palatal, velar, uvular), and not only keep the oral passage watertight, but also create the necessary low pressure required for the suction of small food items, both below and above the water. Indeed, most aquatic mammals are able to suction-feed to some extent, and have smooth, ridge-poor palates. Moreover, specialist suction feeders, such as walruses and globicephaline dolphins, have blunt heads, without beak-like mouths as in typical dolphins, and relatively small and round oral openings [36-39].
These features may be essential prerequisites to the evolution of spoken language, because obstruction of the vocal tract is an elementary requisite for the formation of consonants: complete obstruction in stops (p, d, k etc.) and nasals (m, n etc.), and partial obstruction in gliders (v, z, sh etc.). The sealing of the airways at the oral passage presumably overlaps with the abilities for suction feeding and for underwater feeding. The sealing of the airways at the nasal passage (Table 1) is not discussed in detail here.
Suction feeding is much rarer in terrestrial animals [37, 38]. It is seen in some primates, ursids and bats, who suck the juice from fruits and grubs with protruding lips forming very small mouth openings [24, 39-41]. Sloth bears, orangutans and chimpanzees can strongly protrude the lips creating a small oral opening, but nevertheless have long flat tongues and ridged palates. The typically human oral features such as flat face, small mouth, smooth palate etc. seem to be suited for suction of smooth aquatic foods more than for suction of terrestrial foods. We do not have to chew raw oysters, can swallow food under water, including small fish, and can swim with open mouth under water without swallowing or inhaling water. Feeding under water requires a fine co-ordination of the lips, mouth, tongue and throat in order to keep water out of the airways and prevent ingestion of too much (sea) water. Our extremely flexible globular tongue, in combination with the closed parabolic tooth row and smooth arched palate, is able to close the oral cavity at all possible places, but also manipulate objects within the mouth and help expel water from the mouth.
186 Fifty Years after Alister Hardy Waterside Hypotheses of Human Evolution Vaneechoutte et al
Marc Verhaegen · Study Center Anthropology
When we compare human lips to those of our nearest relatives, there are several differences: the flat face, the existance of a philtrum (groove, furrow or ridge?), the rel.very small mouth, and "fleshy" red lips (covered with mucose instead of skin). As usual, we have to explain these typically human features IMO by our littoral past (Pleistocene archaic Homo dispersing along coasts & rivers): the consumption & suction of soft & slippery foods such as shellfish. The philtrum is discussed by Elaine Morgan 1997 "The aquatic ape hypothesis" Souvenir illustr.p.165. These oral features (lips, but also toothrow, palate, tongue & throat) allowed the production of consonants, an essential part of human speech ( google, eg, "verhaegen speech origins").
As for the earliest oro-facial movements, chimps & human fetuses thumb-suck in the uterus, already at 6 month or earlier IIRC.
Sep 24, 2013
|Website: F. Mansfield, 2015|
Disclaimer: This site is currently under construction. Every effort has been (will be!) made to trace the copyright owners of any images or text used on this site to request permission and to give proper credit. If you are the copyright holder of any images, files or text and have not been contacted, please contact the webmaster in order to rectify this.