Human language has three major components: phonology, semantics, and grammar. These components are acquired successively from about the first, the second and the third year of life (Hirsch-Pasek & Golinkoff 1996). This succession may reflect the human linguistic evolutionary stages: pre-language, one-word sentences, and grammatical or "true" language. This paper discusses the first stage, the phonetic pre-adaptations for language, and is based mostly upon comparative data with other mammals.

Most researchers agree that our remote primate ancestors lived in trees. A number of different hypotheses, however, have been put forward to explain the latter part of our evolutionary history. Recently, there has been a steady accumulation of evidence suggesting that human evolution may not have started in a warm and dry milieu, as the savanna theory used to assert. Instead, the anatomical, physiological, biochemical and palaeo-environmental data suggest that humans may have evolved in warm and wet conditions, perhaps at the edge between land and water (Hardy 1960, Morgan 1997, Bender et al. 1997, Verhaegen 1997, Tobias 1998). More specifically, at the recent symposium on Water and Human Evolution (Ghent, Belgium, 1999), it was proposed that our ancestors may have been coastal or riverside omnivores, which not only consumed terrestrial plants and animals but also collected part of their food in the water. That means their lifestyle may have included wading and even diving for shellfish, seaweeds, crustaceans and fish.

Typically human features such as bipedal locomotion and frequent tool use are occasionally seen in some nonhuman primates. Proboscis monkeys, for example, cross shallow stretches of water on two legs when moving from one mangrove tree to another, and lowland gorillas go wading on their hindlimbs through forest swamps in search of what researchers call aquatic herbaceous vegetation or AHV (Chadwik 1995). In the same way, Pliocene hominids might have waded in shallow waters in forest clearings, gallery forests or mangrove areas, in search of floating fruit, sedges, reeds, AHV, fish and/or shellfish, all of which were probably available, and all of which hominids were probably capable of eating (Sponheimer & Lee-Thorp 1999, DuBrul 1977, Puech et al. 1986, Puech 1992, Broadhurst et al. 1998).

Tool use is seen in sea otters, capuchin monkeys and chimpanzees, which all use stones to crack open hard-shelled foods such as shellfish and nuts (Fernandes 1991). It is possible that human Pliocene ancestors, like mangrove capuchins, manipulated hard objects to remove and open the oysters which grew on the mangrove trees in the areas in which they lived.

Later, during the late Pliocene or early Pleistocene, members of the genus Homo – as opposed to our more distant relatives the australopithecines – might have also learned how to dive and collect deeper shellfish and other aquatic resources. This could explain why humans have such remarkable diving capabilities, particularly when compared to all nonhuman primates (Schagatay 1996). Indeed, Homo fossils – as opposed to Australopithecus – are typically found near shellfish (Chiwondo, Chemeron, Nariokotome, Zhoukoudian, Boxgrove, Terra Amata, Rabat, Hopefield, Gibraltar and others). Homo erectus remains especially have been discovered in marine sediments amid shellfish, barnacles and corals, from the early Pleistocene skull of Mojokerto at Java (Ninkovich & Burckle 1978), to the late Pleistocene Acheulean tools in Eritrea (recent discoveries of Robert Walter and co-workers). Possibly, Homo erectus spread along the Indian Ocean coasts, where they gathered foods from the land and the sea, and where they later followed rivers inland to colonise the interiors of Africa and Eurasia.

Whereas stone tool use for cracking hard-shelled foods may have been a preadaptation for the development of lithic technologies, the diving abilities of our ancestors might have been a preadaptation for the development of voluntary speech. However, like Darwin (1871), we believe human sound production probably has deeper roots, beginning at a time when our ancestors were still arboreal. Comparative studies suggest there may be several, perhaps overlapping, preadaptations for speech, including musical abilities, swallowing musculature, the ability to close the airways, and voluntary control of breathing.

Babies of two or three months produce cooing sounds. This is called vocalising and is performed with the vocal chords in the larynx, without much oral movement. Soon thereafter, even in deaf children, the babbling starts to include labial consonants, and syllables are produced (consonant plus vowel). In babies older than six months, the sound pattern already resembles the native language, and "dialogues" with the mother stimulate the utterances.

The early prelingual sounds, without symbolic meaning, may correspond with the elaborate songs of nonhuman primates like gibbons. Music powerfully affects our emotions (anthems, hymns, marches, love songs), and has always been a territorial and pair- or group-binding behaviour, as it is in other animals. Well-developed musical abilities and duet singing are seen in several monogamous primates like indris, tarsiers, titi monkeys, and gibbons (Darwin 1871). Bonobos engage in group chorusing, and rival males of this species have been observed engaging in vocal duels (De Waal 1997). Some aquatic species like humpback whales (polygynous) also use complex melodic utterances for territorial behaviour. It is known that musical training in young children induces an enlargement of the planum temporale and the auditory cortex in the left brain hemisphere, and can also lead to an improvement in a child’s ability to hear absolute tones (Schlang et al. 1995). Intonation is an indispensable element of all spoken languages, and almost half of the world’s langauges are tonal.

An important development in human infants between four and six months is the descent of the larynx. One possible explanation for laryngeal descent in humans could be the need to breathe a large amount of air in a short period of time to facilitate diving (Morgan 1997).

All humans, unlike nonhuman primates, can learn to dive. Several human populations, such as some Indonesian and Oceanic populations, as well as the Ama of Korea and Japan, still collect shellfish through breath-hold diving, and there is reason to believe that the ancestors of humans, at least since the time of Homo erectus, also had this ability (Schagatay 1996, Verhaegen 1997).

Diving, as seen in aquatic or semi-aquatic mammals, requires a voluntary control of breathing. In contrast with land mammals, divers must be able to take a deep breath just before they intend to dive, and breathe deeper and faster between dives. They must also be able to hold their breath underwater, exactly when their oxygen needs are highest. In contrast, terrestrial mammals intensify their breathing at the moment they need more oxygen; while running, for example. Diving also requires the complete closure of the airways underwater, so that water can be kept out of the lungs.

A descended larynx may also have been a useful adaptation for swallowing certain aquatic foods, such as oysters, and perhaps also for feeding underwater. Other animals featuring a descended larynx include so-called "suction feeders" of seafood or fruits, such as some pinnipeds and some bats (Fay 1982, Negus 1962, Rosewear 1965). Possibly, the laryngeal descent allows considerable retraction of the tongue so that the pressure in the oral cavity can be lowered, which is one possible way to accommodate underwater suction, as in walruses, or for sucking juicy fruits, as in some bats (Fay 1982, Hildebrand 1974, Rosewear 1965, Sprague 1943).

Other adaptations seen in mammals that regularly suction-feed are a small mouth, a smooth and vaulted palate, and a smooth and round tongue that fits nicely in the palate. These features, in different combinations, are seen in sloth bears, some bats and primates that suck insects or fruit pulp, and in particular in walruses and some other pinnipeds that suck shellfish, squid or fish. These features also typically distinguish humans from apes. Chimpanzees have a larger mouth, a flat and rough palate with more transversal ridges, a flat tongue, and no descended larynx (Hocket 1967, Laitman 1985).

The human sucking adaptations could have been used for fruits and/or for smooth aquatic foods. Humans are able to swallow food underwater, and can also keep their mouths open underwater without swallowing or inhaling water. Feeding underwater requires a fine co-ordination of the lips, mouth, tongue and throat in order to keep the water out of the airways. The human tongue is extremely flexible and is well adapted for manipulating objects within the mouth.

Some of these feeding adaptations might explain why our tongue is able to close the oral cavity at different places, allowing a diverse number of consonants to be produced, for example, at the alveolar, palatal, velar and uvular articulation places.

We believe that at least some of these adaptations of the oral cavity and airways were important for the evolution of human speech, and probably came about as a result of our ancestors’ increased diving abilities (Diller 2000). The anatomical mechanisms required for human speech, including voluntary breath control and a well-developed ability to control the lips, tongue and mouth, are, in our opinion, the types of adaptations we could expect to see in a creature shifting from a predominantly climbing/wading existence to an existence based more on wading and diving.

This phase of our evolutionary past was probably also when a major period of encephalization occurred, and may have corresponded with a time when our ancestors were in need of a new, or at least modified, form of communication system. After all, traditional primate communicative devices such as smell and body language – with the exception of facial expression – were probably less effective in a semi-aquatic milieu when compared to a non-aquatic one (Morgan 1997).

In conclusion, we believe that the modifications to our ancestors’ mouth and airways to allow greater breath control for diving, as well as the restructuring of the tongue and mouth to accommodate a more varied diet, probably coincided with an early stage in the expansion of the human neocortex, in particular the areas that controlled the fine movements of the mouth and throat muscles (Brodmann areas 4 and 44). These adaptations, in our opinion, may have been important precursers to the evolution of human speech, particularly when combined with the already well-developed rhythmical, melodic and duetting abilities of our ancient primate ancestors.

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