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Language and life history: A new perspective on the development and evolution of human language

Published online by Cambridge University Press:  09 August 2006

John L. Locke  and
Barry Bogin
John L. Locke*
Affiliation:
Department of SpeechLanguageHearing Sciences, Lehman College, City University of New York, Bronx, NY10468
Barry Bogin*
Affiliation:
Department of Behavioral Sciences, University of MichiganDearborn, Dearborn, MI48128http://casl.umd.umich.edu/faculty/bbogin/
*
john.locke@lehman.cuny.edu
bbogin@umd.umich.edu
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Abstract:

It has long been claimed that Homo sapiens is the only species that has language, but only recently has it been recognized that humans also have an unusual pattern of growth and development. Social mammals have two stages of pre-adult development: infancy and juvenility. Humans have two additional prolonged and pronounced life history stages: childhood, an interval of four years extending between infancy and the juvenile period that follows, and adolescence, a stage of about eight years that stretches from juvenility to adulthood. We begin by reviewing the primary biological and linguistic changes occurring in each of the four pre-adult ontogenetic stages in human life history. Then we attempt to trace the evolution of childhood and juvenility in our hominin ancestors. We propose that several different forms of selection applied in infancy and childhood; and that, in adolescence, elaborated vocal behaviors played a role in courtship and intrasexual competition, enhancing fitness and ultimately integrating performative and pragmatic skills with linguistic knowledge in a broad faculty of language. A theoretical consequence of our proposal is that fossil evidence of the uniquely human stages may be used, with other findings, to date the emergence of language. If important aspects of language cannot appear until sexual maturity, as we propose, then a second consequence is that the development of language requires the whole of modern human ontogeny. Our life history model thus offers new ways of investigating, and thinking about, the evolution, development, and ultimately the nature of human language.

Keywords

adolescencechildhooddevelopmentevolutioninfancyjuvenilitylanguagelife historymodularityspeech
Type
Main Articles
Information
Behavioral and Brain Sciences , Volume 29 , Issue 3 , June 2006 , pp. 259 - 280
Copyright
Copyright © Cambridge University Press 2006

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References

Notes

1. Arbib (2005a; 2005b) has suggested that at some point in evolution, hominins may have used manual gestures and vocal sounds to communicate; the gestures – in pantomime – carrying semantic and possibly sequential information of the sort now conveyed by syntax (Goldstein et al., in press).

2. In human neonates, body weight is nearly twice that of chimpanzees, the difference being due, in large measure, to the abundance of fat. This extra fat provides a source of energy to support the large and still rapidly growing brain of the human infant (Bogin 1999b), which is three times larger than the chimpanzee brain at birth (Martin 1983). In fact, human newborns are neurologically more advanced than eight other mammalian species that have been studied; two months before birth, the human brain is already more developed than the brain of the newborn macaque (Clancy et al. 2001). Further disparities develop at birth, when brain growth tapers off in the other primates, whereas in humans it continues for the next year in a rapid, fetal-like trajectory (Martin 1983). Because of these differences, the brains of human neonates require more nutrition than do the brains of other primate newborns (Leonard & Robertson 1992; see below); and, although comparative data are not readily available, it is clear that social stimulation also plays a significant role in human neurological development (e.g., Rutter & O’Connor 2004).

3. The “grandmother hypothesis” is indirectly relevant to our discussion. Human beings are the only primate species, and one of only a few mammalian species, in which adult females have a menopause and a cessation of ovulation long before death. Women are usually infertile by the age of 50, but may have two decades of post-reproductive life in traditional societies (Pavelka & Fedigan 1991). The “grandmother hypothesis” posits that this post-reproductive stage of life evolved because older women stand to gain more reproductive advantage by helping their daughters and grandchildren than by investing in more children of their own (Bogin & Smith 1996; Hamilton 1966). Hill and Hurtado (1991) tested this prediction against objective ethnographic data derived from their work with the Ache hunter-gatherers of South America. The Ache data show that offspring with grandmothers survive at somewhat higher rates than those without grandmothers, but the effect is not nearly enough to account for menopause. In a review of the Ache data and other cases derived from hunting-gathering and agricultural societies, Austad (1994) found no evidence “that humans can assist their descendants sufficiently to offset the evolutionary cost of ceasing reproduction” (p. 255). Still, interest in the “grandmother hypothesis” continues; Hawkes et al. (1998) used mathematical modeling techniques to show ways that menopause could have evolved under Darwinian selection.

4. When is the human capacity for language, or linguistic communication, fully instated in the young? When does it become fully operational? In the case of printed language, it was once possible to specify the materials that one needed to read, such as the Bible or newspaper, or to link competence to larger individual or cultural and economic goals. In the case of spoken language, there seem to be no clear-cut criteria for mastery. Therefore, the standard that has developed in modern societies, perhaps by default, is linked most immediately to social reactions in childhood and to academic success, including literacy. At the age of six, more than 96% of Midwestern American children pass normed tests that emphasize phonology, morphology, syntax, and vocabulary. These tests are sensitive to language skills that are deemed necessary for success in educational programs (Tomblin et al. 1996).

5. Some of these functions, including sarcasm, joking, and idiomatic interpretation, are handled primarily by the so-called nonlinguistic (right) cerebral hemisphere (cf. McDonald 2000; Paradis 1998; Van Lancker 1990). This could be taken to mean that the way people talk is not a linguistic matter, but traditional definitions of language have emphasized message content and creativity. If rules of use are subsumed under “language,” then the right hemisphere is also “linguistic.”

6. That powerful public men tend to make frequent use of words that are rare, archaic, or esoteric suggests that a command of this material may be related to some other attribute that underlies the ability to persuade or manipulate people. Studies indicate that in modern societies the use of words that are rare, long, abstract, diverse, or unusual is correlated with formal measures of intelligence (Carroll 1993; Gustafsson & Holmberg 1992; Gustafsson & Undheim 1996; Ullstadius et al. 2002; Vetterli & Furedy 1997).

7. In citing anthropological work that concentrates on separate and sometimes “exotic” oral societies, there is a possibility that subgroups within literate societies will be ignored. In a working-class tavern in southern Wisconsin, according to an anthropologist-customer (LeMasters 1975), social success was dependent on “the ability to ‘dish it out’ in the rapid-fire exchange called ‘joshing’ … you have to have a quick retort,” he wrote, “and preferably one that puts you ‘one up’ on your opponent. People who can't compete in the game lose status” (p. 140).

8. After submitting the manuscript, we encountered elements of a similar proposal by Darwin. In The Descent of Man, he suggested that with “varied tones and cadences” our evolutionary ancestors “aroused each other's ardent passions, during their courtship and rivalry” (1879/2004, p. 639).

9. Discrimination against poor speakers does not necessarily begin in juvenility. When several four-year-olds were encouraged to “play store,” an irrelevant utterance by one – a child with limited linguistic skills – caused another boy to advise a peer, “Don't talk to him; he's weird” (Rice 1993). “Preschoolers behave as if they know who talks well and who doesn’t,” observed Hadley and Rice (1991), “and they prefer to interact with those who do” (p. 1315).

10. That females tend to operate covertly should not be taken to mean that they lack the ability to attract attention or to perform. In early modern England, women raised their voices against sexual competitors in a strident and spectacular way. According to Capp (2003), when threats to their marriage arose, wives “showed considerable skill in formulating taunts” (p. 199), calling other women “drunken fuddling fool” and “drunken pocky-faced rogue” (p. 257). When women hurled such insults, it was not unusual for them to be arrested and charged with “scolding” (McIntosh 1998).

11. Clearly, our focus here is on verbal behavior (competition and performance) as enacted by specific activities, such as insulting and joking; particular kinds of material, such as colloquial phrases; and vocal attributes, such as rate, fluency, and rhythm. When it comes to linguistic operations, testosterone – whether naturally high or experimentally administered – may exert the opposite effect by suppressing scores on language tests (Christiansen & Knussmann 1987; van Goozen et al. 1994).

12. However, one might hypothesize that men are superior to women in the use of idiomatic material. It has been demonstrated that the speed and fluency of auctioneering and sports broadcasting reflect use of over-learned material, and men dominate these professions (Kuiper 1996; Pawley 1991). But there may also be a male advantage on measures of speeded articulation; some studies have revealed a trend toward superior performance among juvenile and adolescent males on diadochokinetic tasks (Fletcher 1972; Robb et al. 1985).

13. In young women's ratings of children's conversational speech, the highest degree of variance was accounted for by a dynamic factor that included the attributes: excitable, loud, uncontrolled, bold, active, uninhibited, spontaneous, assertive, and dominant. Overall, ratings were more influenced by quality of speech than sentence complexity and grammaticality (Burroughs & Tomblin 1990). Thus, it is possible that vocal characteristics that are favorably regarded in sexual maturity are already present, to some degree, in earlier stages of development.

14. American trial lawyers are also highly verbal, and voluble, in their personal lives. When Walter (1988) interviewed 34 trial lawyers in her dissertation research, she found that many could not be shut up. In one of her late afternoon interviews, “a lawyer talked for two and a half hours with no sign of concluding, and since he had strayed far from the topic, the interviewer terminated the discourse, or tried to, by physically leaving the office. This lawyer followed and continued speaking up to the door of the elevator” (Walter 1988, pp. 31–32).

15. Goodall (1983) reports that for the period 1965 to 1980 there were 51 births and 49 deaths in one community of wild chimpanzees at the Gombe Stream National Park, Tanzania. During a ten-year period at the Mahale Mountains National Park in Tanzania, researchers counted 74 births, 74 deaths, 14 immigrations, and 13 emigrations in one community (Nishida et al. 1990). Chimpanzee population size in each of these two communities was, by these data, effectively in equilibrium. Any additional delay in age of females at first birth or the time between successful births would probably have produced a decline in population.

16. It must be pointed out that there is uncertainty as to the existence of childhood in early H. erectus and its predecessor species. One line of evidence is based on the formation of tooth crown enamel. This method indicates that Australopithecus, H. habilis, and early H. erectus all matured at a rate faster than living humans and closer to living apes (Dean et al. 2001; Zihlman et al. 2004). The “Mojokerto child” from Java (dated at 1.8 million years ago) is attributed to H. erectus and is the only infant specimen preserved well enough to estimate age at death or cranial capacity. A recent analysis of the infant calvaria (i.e., top portion of the skull) indicates that this hominin died between 0.5 and 1.5 years of age and had achieved 72–84% of adult H. erectus brain size (Coqueugnoit et al. 2004). Another analysis by Anto´n (1997) estimates an age at death of 4 to 6 years. If the younger age at death is correct, then the pattern of brain growth is more similar to chimpanzees than human beings. In fact, the Mojokerto fossil would have grown its brain faster than living chimpanzees (Coqueugnoit et al. 2004). If, however, the later age at death is correct, then Mojokerto followed the human trajectory for brain growth.

17. There is indirect evidence for the reproductive value of human adolescence in the data on nonhuman primates. The first-born infants of monkeys and apes are more likely to die than are those of humans. Studies of yellow baboons (Altmann 1980), toque macaques (Dittus 1977), and chimpanzees (Teleki et al. 1976) show that 50–60% of firstborn offspring die in infancy (between birth and age one year). In huntergather human societies, such as the !Kung, about 44% of children die in infancy (Howell 1979). The human advantage may seem small, but over the vast course of evolutionary time even a 6–16% advantage is a powerful selective force. The !Kung live under very difficult and marginal conditions in a desert environment. Their infant mortality rates are at the extreme high end of human population. For comparison, it may be noted that in most contemporary human societies the infant mortality rate is usually below 20% of live births. The nation of Haiti, for example, is the poorest country in the Western Hemisphere. In 1970 the infant mortality rate was 15% (Bogin 2001). In 1960 in the United States, about 2.5% of all live, firstborn children died before the age of one year (Vavra & Querec 1973).

18. Garstang (1922) also saw phylogeny as “the creation of successive ontogenies” (p. 84), a characterization that prompted Studdert-Kennedy (1991), in recent years, to view human language as the “product of successive ontogenies” (p. 10; also see Studdert-Kennedy 2005).

19. This process, once termed “niche picking” by Scarr and McCartney (1983), has recently been treated in some detail by Odling-Smee et al. (2003), who rightly regard “niche construction” as a vastly underplayed process in the history of evolutionary thinking. A brief but interesting discussion of niche construction is available in Dawkins (2004), who distinguishes this kind of engineered and adaptive alteration, which is encompassed by his extended phenotype theory, from the less Darwinian processes of “niche change.”