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

Locke & Bogin: <strong>Language</strong> <strong>and</strong> <strong>life</strong> <strong>history</strong>In the first, men who speak in a way that secures attentionare also likely to be high in dominance, as we saw insection 4.2. The second relationship is between theattractive or forceful use of speech <strong>and</strong> testosterone.Testosterone is correlated with, <strong>and</strong> may increase, theboldness with which individuals enter a room, <strong>and</strong> thetendency to work in public arenas, such as the theatricalstage or courtroom. Actors generally display high levelsof testosterone (Dabbs et al. 1990; 2001), <strong>and</strong> triallawyers have 30% more testosterone than other types oflawyers (Dabbs et al. 1998).The more specific link to speech is that trial lawyers, asPhilbrick (1949) wrote, “exercise their power in court bymanipulating the thoughts <strong>and</strong> opinions of others” (p. v).They are, according to Dabbs <strong>and</strong> his colleagues, “goodat presenting concrete details in a straight-talking <strong>and</strong>compelling way that dramatically captures the attentionof a jury in trial court” (Dabbs et al. 1998, p. 91). Thereare obvious similarities between trial lawyers <strong>and</strong> the“Big men” of traditional societies. In 1984, there were3,827 members of the American Association of TrialLawyers. Men comprised 99.9% of the membership(Walter 1988), which is nearly 20% more males thanworked as primary care physicians in the following year(Franks & Bertakis 2003). 14 This research suggests thatwomen who are attracted to men with a comm<strong>and</strong>ingway of speaking may get a mate for themselves,<strong>and</strong> father for their children, who has high levels oftestosterone <strong>and</strong> status, <strong>and</strong> unusual access to valuedresources.There are other, more specific connections betweenaspects of the male voice <strong>and</strong> several indices of fitness.These include links between depth of vocal frequency<strong>and</strong> both testosterone (Dabbs & Mallinger 1999; Pedersenet al. 1986) <strong>and</strong> testis volume (Harries et al. 1997), wheretestosterone levels independently predict coital frequency(Halpern et al. 1993; 1998; Udry 1988), social expressivity(Dabbs & Ruback 1988), <strong>and</strong> social dominance (Schaalet al. 1996). Reduced formant dispersion is also correlatedwith skull <strong>and</strong> body size in primates, the magnitudebeing greater in macaques (Fitch 1997) than in humans(González 2004). It is thus unsurprising that our adaptiveancestors availed themselves of this particular medium,which could broadcast fitness information while simultaneouslytransmitting the units of language, to saynothing of the social, indexical, <strong>and</strong> emotional informationthat would have been embedded therein (Cheney &Seyfarth 2005b). Recently, it was reported that in bothmen <strong>and</strong> women, opposite-sex ratings of vocal attractivenesspredicted age of first sexual intercourse, numberof sexual partners, number of competing sexual relationships,<strong>and</strong> number of partners that were involved inother sexual relationships (Hughes et al. 2004). Theauthors concluded that “voice may have been an importantparameter of mate choice” in human evolution (Hugheset al. 2004, p. 303).In the previous sections, we identified several differentforms of selection that may have applied across the wholeof development, from infancy to sexual maturity, includingthe uniquely human stages of childhood <strong>and</strong> adolescence.Our goal in doing so was to offer an evolutionary accountof our species’ capacity to improvise, learn, <strong>and</strong> controlcomplex vocalizations. It is appropriate now that weexamine the evolution of the <strong>new</strong> stages themselves.9. Evolution of the <strong>new</strong> stagesWe have proposed that when childhood exp<strong>and</strong>ed, <strong>new</strong>opportunities arose, especially within families, for thenegotiation of more structured <strong>and</strong> complex forms of vocalization;<strong>and</strong> that with a premium in this context on honestsignaling, benefits would have accrued to families thatwere able to deploy these more complex forms meaningfully,<strong>and</strong> thus to warn, advise, <strong>and</strong> inform each other.We have further proposed that this material, arisingfrom infancy <strong>and</strong> exp<strong>and</strong>ing in childhood, persisted intojuvenility when it contributed to teasing, joking, <strong>and</strong>gossip in both sexes, behaviors that would have facilitatedachievement of group-oriented goals; as well as into adolescence,when performative skills contributed to intrasexualcompetition <strong>and</strong> epigamic selection, reinforcingall previous developments on which those skills depend.We have proposed relationships between language, atrait unique to humans, <strong>and</strong> two ontogenetic stages thatare also unique to humans. To underst<strong>and</strong> the evolutionof language, therefore, we believe it may be necessaryto ask how <strong>and</strong> when these stages came to exist, <strong>and</strong> thiswe attempt to do here. In succeeding sections, we look atevidence for developmental continuity between the levelsof language, <strong>and</strong> interconnections between language <strong>and</strong>the rules <strong>and</strong> skills that influence its use, offering speculationon how these conjunctions may have come about.It is obviously difficult to reconstruct the evolution of<strong>life</strong> <strong>history</strong> stages from fossil remains alone. Fortunately,it is possible to draw relevant inferences from synthesesof comparative anatomical, physiological, <strong>and</strong> ethologicaldata, <strong>and</strong> from archaeological findings. This work is facilitatedby parametric data on the brain <strong>and</strong> body growth ofnonhuman primates, as well as of humans <strong>and</strong> their ancestors(cf. Harvey & Clutton-Brock 1985; Harvey et al. 1987;Martin 1983).9.1. Evolution of childhoodWith an ontogenetic approach to linguistic evolution,structures other than the skull become important. Forexample, teeth <strong>and</strong> jaws are useful because of the strongcorrelation between tooth formation <strong>and</strong> eruption <strong>and</strong>other <strong>life</strong> <strong>history</strong> events (Smith & Tompkins 1995).Figure 3 is an attempt to represent the evolution ofhuman development, though at present the only reliabledata are associated with Pan <strong>and</strong> H. sapiens. Known orestimated adult brain sizes are given at the top of eachbar. Mean age at eruption of the first permanent molar(M1) is graphed across the histograms, <strong>and</strong> identifiednumerically at the base (Smith & Tompkins 1995).Appearing about 3.9 million years ago, Australopithecusafarensis shares many anatomical features with nonhomininpongid (ape) species, including an adult brainsize of about 400 cc <strong>and</strong> a pattern of dental developmentindistinguishable from extant chimpanzees (Conroy &Vannier 1991; Dean et al. 2001; Simons 1989; Smith1991). Therefore, the chimpanzee <strong>and</strong> A. afarensis aredepicted as sharing the typical tripartite stages of postnatalgrowth of social mammals: infancy, juvenility, <strong>and</strong> adulthood(Pereira & Fairbanks 1993). Following the definitionsoffered earlier, infancy represents the period offeeding by lactation, juvenility represents a period offeeding independence prior to sexual maturation, <strong>and</strong>272 BEHAVIORAL AND BRAIN SCIENCES (2006) 29:3