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

More documents

Recommendations

Info

Locke & Bogin: <strong>Language</strong> <strong>and</strong> <strong>life</strong> <strong>history</strong>those children who experience it, but the rate of growthdeclines even in children without a detectable spurt. Thecause of this decrease in growth rate is unknown, butJanson <strong>and</strong> van Schaik (1993) have proposed severalbenefits. The first is that it provides additional time forthe brain growth <strong>and</strong> learning required for reproductivesuccess in various species of social mammals. Social carnivores,elephants, <strong>and</strong> primates must all learn how to livewithin the social hierarchy of the group. Juvenility alsooffers opportunities to learn complex feeding skills suchas how to hunt, how to open fruits or seeds with protectivecoverings, <strong>and</strong> where <strong>and</strong> when to find food. Reproductiveskills must also be learned, including ways to compete formates <strong>and</strong> care for offspring. Joffe (1997) has reportedpositive correlations between the length of juvenility <strong>and</strong>both group size <strong>and</strong> the volume of social areas of the brain.Janson <strong>and</strong> van Schaik (1993) also proposed that slowergrowth reduces feeding competition <strong>and</strong> maintains asmaller body, which is less threatening to adults. Growingup in a social group that is composed of individuals of differentages <strong>and</strong> social status can be difficult. This is especiallytrue for juveniles who must compete with older, moreexperienced, individuals for food, space, <strong>and</strong> otherresources. Fortunately, their relatively small <strong>and</strong> slowlygrowing bodies require less food than adult bodies, <strong>and</strong>may also afford them some protection from adult competition<strong>and</strong> attack as they present a non-threateningjuvenile morphology.In humans, the decline of growth rate bottoms out atabout age 10 years in girls, two years before it does so inmales, <strong>and</strong> this marks the end of the juvenile stage. Asfor the function of juvenility, it seems reasonable tosuppose that in humans, like the other primates, thisstage offers opportunities to prepare for the social complexitiesof adolescence, as well as adulthood. Wepropose that juvenility also provides the young withchances to learn <strong>and</strong> perfect skills associated with thesocial, pragmatic, <strong>and</strong> performative uses of language.2.6. Juvenile languageCoates (1986) has pointed out that, for all the advancesoccurring in childhood, “a knowledge of grammar, phonology<strong>and</strong> [the] lexicon is not enough – it does not make thechild competent; children need to master not only theformal rules of language, but also rules for the appropriateuse of language” (p. 121). To be sure, juvenility accommodatesadditional syntactic advances (cf. Nippold 1998),with some English forms continuing to emerge in earlyadulthood (Marchman et al. 1991), but many of the <strong>new</strong>developments affect performance. These include anincrease in speech-breathing capacity (Engstrom et al.1956; Hoit et al. 1990) <strong>and</strong> further increases in fluency(Starkweather 1987). Prior to the adolescent “voicebreak,” there are anatomical changes that affect the ratioof the fundamental frequency to the ratio of higherformant frequencies (Sachs et al. 1973; also see Austin &Leeper 1975; Vuorenkoski et al. 1978).There are changes, too, that occur beyond the sentencelevel, in the quality of extended discourse <strong>and</strong> narratives(Bamberg 1987; Burleson 1982; Karmiloff-Smith 1985).These pragmatic advances facilitate a variety of sociallyrelevant activities, from gossip to storytelling, <strong>and</strong> contributeto successful competition <strong>and</strong> courtship in the runup to sexual maturity. In Turkey, boys engage in verbalduels – ritualistic insults <strong>and</strong> replies that require “skill inremembering <strong>and</strong> selecting appropriate retorts to provocativeinsults” (Dundes et al. 1970, p. 135). These duelsoccur primarily from ages 8 to 14 years, effectively bridgingjuvenility <strong>and</strong> adolescence.In one sense, juvenility is analogous to infancy. Whereasthe linguistic knowledge <strong>and</strong> structure gained in infancywill help to satisfy the informational needs of childhood,juvenility provides opportunities to achieve the persuasive<strong>and</strong> attractive use of speech, <strong>and</strong> the ability to fluentlymanipulate elaborate <strong>and</strong> socially appropriate utterances,that will be valued in adolescence.2.7. Stage 4: AdolescenceIn humans, uniquely, there is a distinct skeletal growthspurt in both sexes <strong>and</strong> in almost all skeletal elements ofthe body after several years of gently decreasing juvenilegrowth. The onset of this spurt, along with puberty orgonadarche (an event of the neuroendocrine system)marks the onset of adolescence (Bogin 1999b). Neuroendocrinologicalchanges differentially affect the vocaltract <strong>and</strong> fundamental frequency of the two sexes, femalesrevealing negligible changes, males displaying a significantincrease in tract length <strong>and</strong> decrease in frequency, withfurther drops in the transition from adolescence to adulthood(Fitch & Giedd 1999; Lieberman et al. 2001; Pedersenet al. 1986; 1990; Vuorenkoski et al. 1978). The critical variableis testosterone, which increases the length <strong>and</strong> massof the vocal folds, lowers the fundamental frequency, <strong>and</strong>alters the vibratory characteristics of the vocal folds(Abitol et al. 1999; Beckford et al. 1985; Titze 1989).Development of other secondary sexual characteristics<strong>and</strong> a growth spurt in height <strong>and</strong> weight also occur inadolescence. These physical changes are accompanied byintensification of preexisting friendships <strong>and</strong> the developmentof <strong>new</strong> relationships. The <strong>new</strong> affiliations, <strong>and</strong> membershipin peer groups, facilitate intimacy <strong>and</strong> mutualsupport (Whitmire 2000). Adolescence ends with theattainment of adult stature <strong>and</strong> the biosocial skillsneeded for successful reproduction. This occurs, onaverage, at about 19 years of age in women <strong>and</strong> 21 to 25years in men (Bogin 1999b; 2001).It is significant that the secondary sexual development ofboys <strong>and</strong> girls progresses differently through adolescence.Boys become fertile about two years after puberty <strong>and</strong>the onset of the adolescent growth spurt. At this time theystill look like boys, as their body hair, stature, <strong>and</strong> muscularityare still juvenile in appearance. The peak of their growthspurt (called “peak height velocity,” or PHV) is still, onaverage, one year away, <strong>and</strong> patterns of body hair do notbecome adult-like for three years, with a muscle spurt<strong>and</strong> adult stature still four years away (about age 18 onaverage). Girls, in contrast, will have completed abouthalf their breast <strong>and</strong> pubic hair development by the timeof their PHV. Menarche occurs about a year after PHV.At this point in development, girls have the outwardappearance of women, but they are not fertile. Developmentof an adult frequency of ovulation <strong>and</strong> adult size ofthe birth canal do not occur until approximately age 18(Bogin 1999b).Bogin (1999a; 1999b) has hypothesized that thesesex-specific patterns of adolescent development confer264 BEHAVIORAL AND BRAIN SCIENCES (2006) 29:3
Locke & Bogin: <strong>Language</strong> <strong>and</strong> <strong>life</strong> <strong>history</strong>significant reproductive advantages on our species, partlyby allowing adolescents to learn <strong>and</strong> practice adult economic,social, <strong>and</strong> sexual behaviors before reproducing.He noted that girls best learn their adult social roleswhile they are infertile but perceived by adults asmature, whereas boys best learn their adult social roleswhile they are sexually mature but not yet perceived assuch by adults. The perception of fertility in girls allowsthem to enter the social-economic-sexual world of adultwomen, <strong>and</strong> to practice many skills without the risk ofpregnancy. The hormonal status <strong>and</strong> fertility of adolescentboys primes them to attend to the social-economic-sexualworld of adult men. As these boys are still juvenile inoutward development, they can interact <strong>and</strong> learn fromolder adolescents <strong>and</strong> adults without seeming tocompete for important resources, including women. Theyounger adolescent boy can “apprentice” to older adolescents<strong>and</strong> men, make mistakes that would be very costlyto adults, <strong>and</strong> otherwise learn <strong>and</strong> practice skills thatmay be essential to adult survival <strong>and</strong> reproduction.Without the adolescent growth spurt, <strong>and</strong> the sexspecifictiming of maturation events that occur then, thisunique style of social <strong>and</strong> cultural learning could notoccur, but there is considerable variation in the waysadolescence is treated by individual cultures. Humanadolescence is therefore best understood in terms of itsbiological underpinning <strong>and</strong> its cultural manifestations.2.8. Adolescent languageIn adolescence, there are further changes in linguistic communicationin three broad areas. The first is linguisticcontent, including vocabulary, the more nuanced grammaticaloperations, <strong>and</strong> idiomatic phrases (Nippold & Taylor2002), including slang. The second area of adolescentdevelopment involves delivery, including improvement inspeaking rate <strong>and</strong> fluency. There is a huge increase in respiratorycapacity at this stage, which may influence someaspects of speech <strong>and</strong> voice (Cook & Hamann 1961; Hoitet al. 1990). The third area involves a host of functionsthat begin to surface in childhood but flower in adolescence.One such function is social talking, a predominantlyrelational use of speech in which the topic is frequentlyother people (Gottman & Mettetal 1986). This dispositionto gossip steadily increases during adolescence, especiallyin females (Raffaelli & Duckett 1989; also see sect. 6),whereas the tendency to tease peers is more evidentin males (see review in Eckert 2003). Other functions –several, like gossip, falling outside the area of pragmaticsas usually defined – include joking, deceiving, mollifying,negotiating, <strong>and</strong> persuading, with increases in the use ofsarcasm (McTear & Conti-Ramsden 1992; Nippold 1998;Paul 1995). These skills are not highly appraised by classroomteachers <strong>and</strong> language clinicians, who place a highervalue on the logical expression of thought (Reed et al.1998; Reed & Spicer 2003), but they facilitate achievementof two things that matter a great deal toadolescents <strong>and</strong> adults: status <strong>and</strong> relationships. 5This discussion of the emergence of grammatical <strong>and</strong>pragmatic functions should not distract us from a basicfact about the role of language in this stage of <strong>life</strong>. Adolescentsdo not merely learn additional linguistic features <strong>and</strong>practice <strong>new</strong> rules of usage. They also modify materiallearned in earlier stages, thereby changing aspects oftheir native language (Eckert 1999; Labov 2001).Because adolescents are more parentally independentthan ever, but still geographically limited, a strong localaffiliation tends to influence their personal <strong>and</strong> social identity.An effective way to signal this affiliation <strong>and</strong> increasingautonomy is through linguistic markers, particularlyphonetic <strong>and</strong> vocal ones. “The relatively high degree ofphonological innovation in the adolescent age group,”wrote Eckert (1988), “is an indication that the developmentof adolescent social structure provides a majorimpetus for phonological change” (p. 197).3. How did vocal-verbal behavior evolve?Reports suggest that apes <strong>and</strong> monkeys do not vocalize asoften as humans. Wild chimpanzees are silent much of thetime (Gardner et al. 1989), evidently preferring the manualto the vocal modality (Tomasello et al. 1985; 1989). Trivers(1974) once commented that gorillas appeared to be“selected for silence.” By contrast, our own species isgiven to near-constant chatter in familiar social circumstanceseven when it appears that very little is beingsaid (Locke 1998c). How – under what environmentalpressures – did human sound-making capacities evolve?3.1. Natural selectionTo evolve, biological traits must offer a selective advantage,even if it is small <strong>and</strong> inconsistent, <strong>and</strong> this advantagewill usually be linked to food, defense, reproduction, orsome combination of these. Building on key contributionsin evolutionary biology (Dawkins 1986; Maynard Smith1969), Pinker <strong>and</strong> Bloom (1990) argued that natural selectionis the only way to explain the origin of language <strong>and</strong>other complex abilities. In doing so, they said little aboutany role that selection might have played in development.But as Hogan (1988) has pointed out, natural selection“should operate at all stages of development, <strong>and</strong> notonly on the adult outcome, since any developmentalprocess that reduces the probability of reaching adulthoodwill be very strongly selected against” (p. 97). Hence, webegin this section with several <strong>new</strong> proposals relating tovocal <strong>and</strong> verbal selection as it may have operated ininfancy <strong>and</strong> childhood.3.2. Parental selectionWith evolutionary changes that narrowed the female pelvis<strong>and</strong> deferred fetal brain development (sect. 2.1), infants’need of care would have increased. As care requirementsgrew, conflict <strong>and</strong> competition between the infant <strong>and</strong>its parents would also have escalated. Responsibility forone solution, according to Trivers (1974), would havebeen borne largely, but not exclusively, by the infant – abehavioral change that included more effective use ofcare-elicitation signals, <strong>and</strong> possibly an improvement inthe signals themselves.The parental selection hypothesis proposes that someof the vocal ability presupposed by spoken languagesemerged from infancy, having been asserted initially byhominin infants <strong>and</strong> supported by interactions with theirparents (Locke 2006). According to the hypothesis,infants who issued more effective care-elicitation signalsBEHAVIORAL AND BRAIN SCIENCES (2006) 29:3 265
Page 3 and 4: Locke & Bogin: Language</st
Page 5: Locke & Bogin: Language</st
Page 23 and 24: Commentary/Locke & Bogin: L
Page 43 and 44: Response/Locke & Bogin: Lan
Page 55 and 56: References/Locke & Bogin: L
Page 57 and 58:
References/Locke & Bogin: L
Page 59 and 60:
Page 61 and 62:
Page 63 and 64:
Page 65 and 66:
Page 67:
show all

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

Create successful ePaper yourself

Delete template?

Save as template?