Language and life history: A new perspective on the development ...

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Locke & Bogin: <strong>Language</strong> <strong>and</strong> <strong>life</strong> <strong>history</strong>rarely invoked in theories of evolution) may assume botha direct <strong>and</strong> an indirect form. In the direct case, behaviorsof the young (e.g., infants’ strategic use of creative <strong>and</strong>complex vocalizations) forestall withdrawal of care,increasing the probability of survival to reproductive age.In the indirect form, it is the behavior of sexually matureindividuals that is selected, typically in the quest forstatus <strong>and</strong> mating opportunities, but that behavior is onlyavailable to be selected because it, or a precursive form,has a prior developmental <strong>history</strong>. These cases of selectionin adolescence or early adulthood automatically reinforcethe earlier, enabling behaviors.In other primates, it has been proposed that the juvenileperiod is beneficial because it permits developing animalsto prepare for the complexities of adult behavior. Similarly,we reasoned that human juvenility may have provideda period in which capabilities emerging inprevious stages could be “practiced,” <strong>and</strong> then, in adolescence,more fully exercised for social <strong>and</strong> sexual purposes.Although we suggested that selection operated throughoutontogeny, we also speculated that in adolescence, performativebehaviors (including socially attractive aspects ofarticulate vocalization) increased fitness, established apreferred mode of expression, <strong>and</strong> laid the groundworkfor speech as the universal modality of language.We based our speculation, in part, on anthropologicalreports indicating that in oral societies – which lack thewritten language bias of modern cultures <strong>and</strong> modernLinguistics – fluent, rhythmic, <strong>and</strong> elegant speech attractsattention <strong>and</strong> facilitates the acquisition of status <strong>and</strong>power. This trend is most evident in the case of men, incontrast with the “female advantage” that has beenreported in the psychometric literature, discouraging theoristsin search of a selection-based model in which malesdisplay, <strong>and</strong> are chosen for, their verbal talent. Witnessinga male bias for performative speech, we speculated thatselection produced sex differences that remain evident inverbal behavior today.If childhood entered the human genome first, theamount of vocal-motor control available to our premodernancestors may have remained limited, even if enhanced injuvenility, until the evolution of adolescence. Then, theperformative applications of such behaviors, <strong>and</strong> the behaviorsthemselves, would almost certainly have diversified.Hence, we think there may have been a long period inevolutionary <strong>history</strong> in which vocal behaviors were displayedwithin a familial context, before adolescenceteased them into the open in more elaborate form.We proposed that important aspects of language cannotdevelop until sexual maturity because functions thatemerge at that stage played, <strong>and</strong> still play, a key role inits construction. When selection for vocal <strong>and</strong> verbalperformance in adolescence reinforced previous developments,it swept specializations associated with speech <strong>and</strong>voice, linguistic content <strong>and</strong> structure, <strong>and</strong> rules of usageinto one large specialization. It is difficult to escape theconclusion that the faculty of language includes severaldisparate capabilities, <strong>and</strong> that these capabilities werestitched together in evolution, as they are in moderntimes, by the whole of human ontogeny.ACKNOWLEDGMENTSThe authors wish to acknowledge helpful discussions with, orcomments by, Tom Dickins, Tecumseh Fitch, Cathy Flanagan,Gilbert Gottlieb, Peter LaFreniere, Kim Oller, CatherineSnow, <strong>and</strong> especially, Michael Studdert-Kennedy.NOTES1. Arbib (2005a; 2005b) has suggested that at some point inevolution, hominins may have used manual gestures <strong>and</strong> vocalsounds to communicate; the gestures – in pantomime – carryingsemantic <strong>and</strong> possibly sequential information of the sort nowconveyed by syntax (Goldstein et al., in press).2. In human neonates, body weight is nearly twice that ofchimpanzees, the difference being due, in large measure, tothe abundance of fat. This extra fat provides a source of energyto support the large <strong>and</strong> still rapidly growing brain of thehuman infant (Bogin 1999b), which is three times larger thanthe chimpanzee brain at birth (Martin 1983). In fact, human<strong>new</strong>borns are neurologically more advanced than eight othermammalian species that have been studied; two monthsbefore birth, the human brain is already more developed thanthe brain of the <strong>new</strong>born macaque (Clancy et al. 2001).Further disparities develop at birth, when brain growth tapersoff in the other primates, whereas in humans it continues forthe next year in a rapid, fetal-like trajectory (Martin 1983).Because of these differences, the brains of human neonatesrequire more nutrition than do the brains of other primate <strong>new</strong>borns(Leonard & Robertson 1992; see below); <strong>and</strong>, althoughcomparative data are not readily available, it is clear that socialstimulation also plays a significant role in human neurologicaldevelopment (e.g., Rutter & O’Connor 2004).3. The “gr<strong>and</strong>mother hypothesis” is indirectly relevant to ourdiscussion. Human beings are the only primate species, <strong>and</strong> oneof only a few mammalian species, in which adult females have amenopause <strong>and</strong> a cessation of ovulation long before death.Women are usually infertile by the age of 50, but may have twodecades of post-reproductive <strong>life</strong> in traditional societies(Pavelka & Fedigan 1991). The “gr<strong>and</strong>mother hypothesis”posits that this post-reproductive stage of <strong>life</strong> evolved becauseolder women st<strong>and</strong> to gain more reproductive advantage byhelping their daughters <strong>and</strong> gr<strong>and</strong>children than by investing inmore children of their own (Bogin & Smith 1996; Hamilton1966). Hill <strong>and</strong> Hurtado (1991) tested this prediction againstobjective ethnographic data derived from their work with theAche hunter-gatherers of South America. The Ache data showthat offspring with gr<strong>and</strong>mothers survive at somewhat higherrates than those without gr<strong>and</strong>mothers, but the effect is notnearly enough to account for menopause. In a review of theAche data <strong>and</strong> other cases derived from hunting-gathering <strong>and</strong>agricultural societies, Austad (1994) found no evidence “thathumans can assist their descendants sufficiently to offset the evolutionarycost of ceasing reproduction” (p. 255). Still, interest inthe “gr<strong>and</strong>mother hypothesis” continues; Hawkes et al. (1998)used mathematical modeling techniques to show ways thatmenopause could have evolved under Darwinian selection.4. When is the human capacity for language, or linguisticcommunication, fully instated in the young? When does itbecome fully operational? In the case of printed language, itwas once possible to specify the materials that one needed toread, such as the Bible or <strong>new</strong>spaper, or to link competence tolarger individual or cultural <strong>and</strong> economic goals. In the case ofspoken language, there seem to be no clear-cut criteria formastery. Therefore, the st<strong>and</strong>ard that has developed in modernsocieties, perhaps by default, is linked most immediately tosocial reactions in childhood <strong>and</strong> to academic success, includingliteracy. At the age of six, more than 96% of MidwesternAmerican children pass normed tests that emphasize phonology,morphology, syntax, <strong>and</strong> vocabulary. These tests are sensitiveto language skills that are deemed necessary for success ineducational programs (Tomblin et al. 1996).5. Some of these functions, including sarcasm, joking, <strong>and</strong>idiomatic interpretation, are h<strong>and</strong>led primarily by the so-callednonlinguistic (right) cerebral hemisphere (cf. McDonald 2000;278 BEHAVIORAL AND BRAIN SCIENCES (2006) 29:3
Locke & Bogin: <strong>Language</strong> <strong>and</strong> <strong>life</strong> <strong>history</strong>Paradis 1998; Van Lancker 1990). This could be taken to meanthat the way people talk is not a linguistic matter, but traditionaldefinitions of language have emphasized message content <strong>and</strong>creativity. If rules of use are subsumed under “language,” thenthe right hemisphere is also “linguistic.”6. That powerful public men tend to make frequent use ofwords that are rare, archaic, or esoteric suggests that acomm<strong>and</strong> of this material may be related to some other attributethat underlies the ability to persuade or manipulate people.Studies indicate that in modern societies the use of words thatare rare, long, abstract, diverse, or unusual is correlated withformal 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<strong>and</strong> sometimes “exotic” oral societies, there is a possibilitythat subgroups within literate societies will be ignored. In aworking-class tavern in southern Wisconsin, according to ananthropologist-customer (LeMasters 1975), social success wasdependent on “the ability to ‘dish it out’ in the rapid-fireexchange called ‘joshing’ ... you have to have a quick retort,”he wrote, “<strong>and</strong> preferably one that puts you ‘one up’ on youropponent. People who can’t compete in the game lose status”(p. 140).8. After submitting the manuscript, we encountered elementsof a similar proposal by Darwin. In The Descent of Man, hesuggested that with “varied tones <strong>and</strong> cadences” our evolutionaryancestors “aroused each other’s ardent passions, during theircourtship <strong>and</strong> rivalry” (1879/2004, p. 639).9. Discrimination against poor speakers does not necessarilybegin in juvenility. When several four-year-olds were encouragedto “play store,” an irrelevant utterance by one – a child withlimited linguistic skills – caused another boy to advise a peer,“Don’t talk to him; he’s weird” (Rice 1993). “Preschoolersbehave as if they know who talks well <strong>and</strong> who doesn’t,” observedHadley <strong>and</strong> Rice (1991), “<strong>and</strong> they prefer to interact with thosewho do” (p. 1315).10. That females tend to operate covertly should not be takento mean that they lack the ability to attract attention or toperform. In early modern Engl<strong>and</strong>, women raised their voicesagainst sexual competitors in a strident <strong>and</strong> spectacular way.According to Capp (2003), when threats to their marriagearose, wives “showed considerable skill in formulating taunts”(p. 199), calling other women “drunken fuddling fool” <strong>and</strong>“drunken pocky-faced rogue” (p. 257). When women hurled suchinsults, it was not unusual for them to be arrested <strong>and</strong> chargedwith “scolding” (McIntosh 1998).11. Clearly, our focus here is on verbal behavior (competition<strong>and</strong> performance) as enacted by specific activities, suchas insulting <strong>and</strong> joking; particular kinds of material, such as colloquialphrases; <strong>and</strong> vocal attributes, such as rate, fluency, <strong>and</strong>rhythm. When it comes to linguistic operations, testosterone –whether naturally high or experimentally administered – mayexert the opposite effect by suppressing scores on languagetests (Christiansen & Knussmann 1987; van Goozen et al.1994).12. However, one might hypothesize that men are superior towomen in the use of idiomatic material. It has been demonstratedthat the speed <strong>and</strong> fluency of auctioneering <strong>and</strong> sportsbroadcasting reflect use of over-learned material, <strong>and</strong> mendominate these professions (Kuiper 1996; Pawley 1991). Butthere may also be a male advantage on measures of speededarticulation; some studies have revealed a trend toward superiorperformance among juvenile <strong>and</strong> adolescent males on diadochokinetictasks (Fletcher 1972; Robb et al. 1985).13. In young women’s ratings of children’s conversationalspeech, the highest degree of variance was accounted for by adynamic factor that included the attributes: excitable, loud,uncontrolled, bold, active, uninhibited, spontaneous, assertive,<strong>and</strong> dominant. Overall, ratings were more influenced by qualityof speech than sentence complexity <strong>and</strong> grammaticality(Burroughs & Tomblin 1990). Thus, it is possible that vocalcharacteristics that are favorably regarded in sexual maturityare already present, to some degree, in earlier stages ofdevelopment.14. American trial lawyers are also highly verbal, <strong>and</strong> voluble,in their personal lives. When Walter (1988) interviewed 34 triallawyers in her dissertation research, she found that many couldnot be shut up. In one of her late afternoon interviews, “alawyer talked for two <strong>and</strong> a half hours with no sign of concluding,<strong>and</strong> since he had strayed far from the topic, the interviewerterminated the discourse, or tried to, by physically leaving theoffice. This lawyer followed <strong>and</strong> continued speaking up to thedoor of the elevator” (Walter 1988, pp. 31–32).15. Goodall (1983) reports that for the period 1965 to 1980there were 51 births <strong>and</strong> 49 deaths in one community of wildchimpanzees at the Gombe Stream National Park, Tanzania.During a ten-year period at the Mahale Mountains NationalPark in Tanzania, researchers counted 74 births, 74 deaths, 14immigrations, <strong>and</strong> 13 emigrations in one community (Nishidaet al. 1990). Chimpanzee population size in each of these twocommunities was, by these data, effectively in equilibrium. Anyadditional delay in age of females at first birth or the timebetween successful births would probably have produced adecline in population.16. It must be pointed out that there is uncertainty as to theexistence of childhood in early H. erectus <strong>and</strong> its predecessorspecies. One line of evidence is based on the formation oftooth crown enamel. This method indicates that Australopithecus,H. habilis, <strong>and</strong> early H. erectus all matured at a rate fasterthan living humans <strong>and</strong> closer to living apes (Dean et al. 2001;Zihlman et al. 2004). The “Mojokerto child” from Java (datedat 1.8 million years ago) is attributed to H. erectus <strong>and</strong> is theonly infant specimen preserved well enough to estimate ageat death or cranial capacity. A recent analysis of the infant calvaria(i.e., top portion of the skull) indicates that this hominindied between 0.5 <strong>and</strong> 1.5 years of age <strong>and</strong> had achieved72–84% of adult H. erectus brain size (Coqueugnoit et al.2004). Another analysis by Antón (1997) estimates an age atdeath of 4 to 6 years. If the younger age at death is correct,then the pattern of brain growth is more similar to chimpanzeesthan human beings. In fact, the Mojokerto fossil wouldhave grown its brain faster than living chimpanzees(Coqueugnoit et al. 2004). If, however, the later age at deathis correct, then Mojokerto followed the human trajectory forbrain growth.17. There is indirect evidence for the reproductive value ofhuman adolescence in the data on nonhuman primates. Thefirst-born infants of monkeys <strong>and</strong> apes are more likely to diethan are those of humans. Studies of yellow baboons (Altmann1980), toque macaques (Dittus 1977), <strong>and</strong> chimpanzees(Teleki et al. 1976) show that 50–60% of firstborn offspringdie in infancy (between birth <strong>and</strong> age one year). In huntergatherhuman societies, such as the !Kung, about 44% of childrendie in infancy (Howell 1979). The human advantage mayseem small, but over the vast course of evolutionary time evena 6–16% advantage is a powerful selective force. The !Kunglive under very difficult <strong>and</strong> marginal conditions in a desertenvironment. Their infant mortality rates are at the extremehigh end of human population. For comparison, it may benoted that in most contemporary human societies the infantmortality rate is usually below 20% of live births. The nationof Haiti, for example, is the poorest country in the WesternHemisphere. In 1970 the infant mortality rate was 15%(Bogin 2001). In 1960 in the United States, about 2.5% ofall live, firstborn children died before the age of one year(Vavra & Querec 1973).18. Garstang (1922) also saw phylogeny as “the creation ofsuccessive ontogenies” (p. 84), a characterization that promptedStuddert-Kennedy (1991), in recent years, to view humanBEHAVIORAL AND BRAIN SCIENCES (2006) 29:3 279
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