Over the holiday break I noticed an ad that had appeared on New York's subways, saying in very large letters, "Never shake your baby." The need for such warnings is a reminder of how maddening the unrelenting demands of a baby can be. Recently several scholars have brought that issue to a consideration of speech origins. Notably, last summer there was an extensive discussion in Behavioral and Brain Sciences about "Language and Life History: A New Perspective on the Development and Evolution of Language" by John L. Locke and Barry Bogin (Links to abstracts and open peer commentary here.) After reading it I feel I have a better sense of why most parents don't slip up and shake their babies to death.
The question of why parents bother to raise their children all the way to adulthood is shocking, of course, infanticide being generally frowned on, and in some sense ridiculous, since raising another generation is so central to evolution’s operation. So my question does not look for a way to explain something surprising. Rather, how do we explain something so mundane?
The answer proposed by Locke and Bogin is that human parents and infants form an especially strong bond through the course of infancy by vocalizing. The standard parry to the idea that speech arose to promote bonding is that this explanation has nothing to say about the rise of meaningful or syntactic speech. Why not just make random, soft sounds?
But of course random soft sounds are exactly what infants make.
At seven months, infants typically begin to make alternating jaw movements while phonating, an act that produces well-formed syllables. An apparently universal phonetic repertoire begins to emerge at this time. Four months later, infants utter sounds in ways that reflect prior exposure to speech. (p. 261)
In other words, at 7 months, infants start to babble, making vowel sounds of the ta-ta, goo-goo variety. This vocalizing is usually understood to be some sort of precursor to speech, and that is the way Locke and Bogins treat it, but there they go beyond their data. As one of the commentators in the “open peer” discussion says, the different abilities required for speech “might have [been established by] different selective pressures.” (Daniela Lenti Boero and Luciana Bottoni , “From crying to words: Unique or multilevel selective pressures?” p. 292; abstract here.)
The idea that different abilities may have different evolutionary origins sounds obvious, but it must be kept in mind when thinking about the origins of speech. Talking is so complex and depends on many different abilities that we have to remind ourselves the elements supporting our speech faculty probably did not all appear on the same day. The most basic speaking skill, of course, is the ability to make the sounds of language. Where did that capacity come from? There seem to be two possible ways:
- Direct route (adaptation): We started to use words and then natural selection pressed us to develop more control so that we could use more words and distinguish between them more easily.
- Indirect route (exaptation): We developed the ability to make and control sounds for some non-linguistic reason and then put the skill to further use by uttering words.
On this blog selection for a “non-linguistic reason” means a skill was selected for some reason other than promoting the ability to create an attention triplet (speaker, listener, topic). Locke and Bogin favor this indirect route of selection: syllabic vocalization arose as a side effect of the evolution of an ability to create an emotional bond between parents and infant. (Infancy in primates can be defined as the period from birth to the end of breastfeeding.)
The suggestion that syllabic vocalization supports emotional bonding is seconded by part of the open commentary, in a piece by D. Kimbrough Oller and Ulrike Griebel, “How the language capacity was naturally selected: Altriciality and long immaturity.” (Abstract here.) They report:
It also bears emphasizing that even in the first six months of human life, vocal development is remarkable, and appears to bring the infant to a point of functional and contextual flexibility in production and use of vocalization that is never achieved in any nonhuman primate. The foundations laid in the first six months appear to be critical to all subsequent development toward vocal language [i.e., speech] … it is sensible to conclude that our hominid ancestors, as they broke away from the primate background, prior to possessing language must have developed command of vocal flexibility, because without it, all further evolution in the direction of vocal language may well have been impossible. … The unique topography and richness of human parent-infant face-to-face vocal interactions strongly suggests bonding is at stake… (p. 294)
This kind of argument raises many other questions: why such vocalization only in humans? Why is such bonding needed? What kind of selective process was involved? But this is a blog, not a thesis, and we cannot cover everything in one post. Locke and Bogin addressed these questions and so did Oller and Griebel’s peer comment. We will get to them eventually, but today I want to focus simply on the fact that two strands of peculiarly human communication are becoming apparent on this blog, one is emotional, the other meaningful, and both of them are critical to building and maintaining a community through joint attention.
The emotional side is more musical and binds together people jointly attending to the sounds (see post: Music Creates Community) while the meaningful side adds a topic to the joint attention. Perhaps that classic distinction between sound and topic suggests why the most powerful expressions are poetic, liturgical, or operatic. Each of them unites emotional and meaningful communication into one experience.
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