The brains of other species have nothing like the neurons and networks that support the 6,000 or so human languages. Many other animals communicate, but their language is primitive. The human linguistic ability at age 2 far surpasses that of full-grown adults from every other species. How do babies do it? Part of the answer is that learning language is a priority; babies listen intensely, figuring out speech. One scholar explains “infants are acquiring much of their native language before they utter their first word” (Aslin, 2012, p. 191).

187

The sequence of language development is the same worldwide (see At About This Time). Some children learn several languages, some only one; some learn rapidly and others slowly, but they all follow the same path. Even deaf infants who become able to hear (thanks to cochlear implants) follow the sequence, catching up to their age-mates unless they have multiple disabilities (Fazzi et al., 2011). Those who learn sign language also begin with one word at a time, and then sign sentences of increasing length and complexity.

Newborns prefer to listen to the language their mother spoke when they were in the womb, not because they understand the words, of course, but because they are familiar with the rhythm, the sounds, and the cadence.

Surprisingly, newborns of bilingual mothers differentiate between both languages (Byers-Heinlein et al., 2010). Data were collected on 94 newborns (age 0 to 5 days) in a large hospital in Vancouver, Canada. Half were born to mothers who spoke both English and Tagalog (a native language of the Philippines), one-third to mothers who spoke only English, and one-sixth to mothers who spoke English and Chinese. The bilingual mothers used English in more formal contexts and non-English with family.

188

The infants in all three groups sucked on a pacifier connected to a recording of 10 minutes of English or Tagalog matched for pitch, duration, and number of syllables. As evident in the frequency and strength of their sucking, most of the infants with bilingual mothers preferred Tagalog, presumably because their mothers were likely to speak English in formal settings but Tagalog when with family and friends, whereas those with monolingual mothers preferred English.

The Chinese bilingual babies (who had never heard Tagalog) nonetheless preferred it. The researchers believe that they liked Tagalog because the rhythm of that language is more similar to Chinese than to English (Byers-Heinlein et al., 2010).

Similar results, showing that babies like to hear familiar language, come from everyday life. Young infants attend to voices more than to mechanical sounds (a clock ticking) and look closely at the facial expressions of someone talking to them (Minagawa-Kawai et al., 2011). By 6 months, by observing mouth movements alone (no sound), they can decipher whether or not that person is speaking their native language (Weikum et al., 2007). By 1 year, they are more likely to imitate the actions of a stranger speaking their native language than those of a person who speaks another language (Buttelmann et al., 2013).

Infants’ ability to distinguish sounds they hear improves, whereas the ability to hear sounds never spoken in their native language (such as how an “r” or an “l” is pronounced) deteriorates (Narayan et al., 2010). If parents want a child to be fluent in two languages, they should speak both of them to their baby.

In every language, adults use higher pitch, simple words, repetition, varied speed, and exaggerated emotional tone when talking to infants (Bryant & Barrett, 2007). This special language form is sometimes called baby talk, since it is directed to babies, and sometimes called motherese, since mothers universally speak it. Nonmothers speak it as well. For that reason, scientists prefer the more formal term, child-directed speech.

No matter what term is used, child-directed speech fosters learning, and babies communicate as best they can. By 4 months, they squeal, growl, gurgle, grunt, croon, and yell, telling everyone what is on their minds in response to both their own internal state and their caregivers’ words. At 7 months, infants begin to recognize words that are highly distinctive (Singh, 2008): Bottle, dog, and mama, for instance, might be differentiated, but words that sound alike (baby, Bobbie, and Barbie) are not.

Not only do infants prefer child-directed speech; they also like alliteration, rhymes, repetition, melody, rhythm, and varied pitch (Hayes & Slater, 2008; Schön et al., 2008). Think of your favorite lullaby (itself an alliterative word); obviously, babies prefer sounds over content.

Between 6 and 9 months, babies repeat certain syllables (ma-ma-ma, da-da-da, ba-ba-ba), a vocalization called babbling because of the way it sounds. Babbling is experience-expectant; all babies babble, even deaf ones. Since babies like to make interesting sights last, as Piaget found, babbling increases in response to child-directed speech. Deaf babies stop babbling but increasingly engage in responsive gesturing.

Toward the end of the first year, babbling begins to sound like the infant’s native language; infants imitate accents, cadence, consonants, and so on. Videos of deaf infants whose parents sign to them show that 10-month-olds use about a dozen distinct hand gestures in a repetitive manner similar to babbling.

189

Many caregivers, recognizing the power of gestures, teach “baby signs” to their 6- to 12-month-olds, who communicate with hand signs months before they move their tongues, lips, and jaws to make specific words. There is no evidence that baby signing accelerates talking (as had been claimed), but it may make parents more responsive, which itself is an advantage (Kirk et al., 2013).

One early gesture is pointing, an advanced social gesture that requires understanding another person’s perspective. Most animals cannot interpret pointing; most 10-month-old humans look toward wherever someone else points and can already use a tiny index finger (not just a full hand) to point themselves, even to a place where an object belongs but is not yet there (Liszkowski et al., 2009; Liszkowski & Tomasello, 2011). Pointing is well developed by 12 months, especially when the person who is pointing also speaks (e.g., “look at that”) (Daum et al., 2013).

Babbling and gesturing before speech vary from infant to infant—sometimes for biological reasons, sometimes for social ones. Developmentalists can detect early signs of autism, attention-deficit/hyperactivity disorder, hearing impairment, and dyslexia by examining videos of the communication patterns of young infants. However, definitive diagnosis is not possible simply by observation in the early months.

Finally, at about 1 year, the average baby utters a few words, understood by caregivers if not by strangers. For example at 13 months, a child named Kyle knew standard words such as mama, but he also knew da, ba, tam, opma, and daes, which his parents knew to be, respectively, “downstairs,” “bottle,” “tummy,” “oatmeal,” and “starfish.” He also had a special sound that he used to call squirrels (Lewis et al., 1999).

In the first months of the second year, spoken vocabulary increases gradually (perhaps one new word a week). A 12-month-old who speaks two words might not speak eight words until several weeks later. However, meanings are learned rapidly; babies understand about 10 times more words than they can say.

Initially, the first words are merely labels for familiar things (mama and dada are common), but early words are soon accompanied by gestures, facial expressions, and nuances of tone, loudness, and cadence (Saxton, 2010). Imagine meaningful communication in “Dada,” “Dada?,” and “Dada!” Each is a holophrase, a single word that expresses an entire thought.

Intonation (variation in tone and pitch) is extensive in both babbling and holophrases, but there sometimes is a lull between the age of babbling and the age of recognizable words. Apparently at about 1 year, infants reorganize their vocalization from universal to language-specific. They are no longer just making noises; they are trying to communicate in a specific language.

Uttering meaningful words takes all their attention—none is left over for intonation. Careful tracing of early language finds other times when vocalization slows before a burst of new talking; perception affects action (Pulvermüller & Fadiga, 2010), and neurological advances may temporarily inhibit speech (Parladé & Iverson, 2011).

190

Spoken vocabulary builds rapidly once the first 50 words are mastered, with 21-month-olds typically saying twice as many words as 18-month-olds (Adamson & Bakeman, 2006). This language spurt is called the naming explosion because many early words are nouns, that is, names of persons, places, or things.

Between 12 and 18 months, almost every infant learns the name of each significant caregiver (often dada, mama, nana, papa, baba, tata) and sibling (and sometimes each pet). Other frequently uttered words refer to the child’s favorite foods (nana can mean “banana” as well as “grandma”) and to elimination (pee-pee, wee-wee, poo-poo, ka-ka, doo-doo).

Notice that all these words have two identical syllables, each a consonant followed by a vowel. Many words follow that pattern—not just baba but also bobo, bebe, bubu, bibi. Other early words are only slightly more complicated—ma-me, ama, and so on. The meaning of these words varies by language, but every baby says such words, and everywhere culture assigns meaning to them.

Cultures and families vary in how much child-directed speech children hear. Some parents read to their infants, teach them signs, and respond to every burp or fart as if it were an attempt to talk. Other parents are much less verbal. They use gestures and touch; they say “hush” and “no” instead of expanding vocabulary.

By 5 months, babies prefer adults who often use child-directed speech, even when those talkative adults are temporarily silent. Apparently, just as infants seek to master motor skills as soon as they can, they seek to learn language from the best teachers available (Schachner & Hannon, 2011).

Cultural differences are readily apparent in what linguistic sounds capture attention. Infants soon favor the words, accents, and linguistic patterns of their home language. For instance, a study of preverbal Japanese and French infants found that words with the first consonant at the front of the mouth and the second consonant at the back (as in “bat”) was preferred by infants in France, but the opposite (as in “tap”) was true in Japan. This was the case because of the language (French or Japanese) the babies had heard (Gonzalez-Gomez et al., 2014).

The traditional idea that children should be “seen but not heard” is contrary to what developmentalists recommend and many contemporary families do—encourage talking. By contrast, many other families value children who listen respectfully without talking. Everywhere, however, infants listen to whatever speech they hear and appreciate the sounds of their culture. Even musical tempo is culture-specific: 4- to 8-month-olds seem to like their own native music best (Soley & Hannon, 2010).

191

Although all new talkers say names, use similar sounds, and prefer nouns more than other parts of speech, the ratio of nouns to verbs and adjectives varies from place to place (Waxman et al., 2013). For example, by 18 months, English-speaking infants speak far more nouns than verbs compared to Chinese or Korean infants. Why?

One explanation goes back to the language itself. The Chinese and Korean languages are “verb-friendly” in that verbs are placed at the beginning or end of sentences. That facilitates learning. By contrast, English verbs occur anywhere in a sentence, and their forms change in illogical ways (e.g., go, gone, will go, went). This irregularity may make English verbs harder to learn, although the fact that English verbs often have distinctive suffixes (-ing, -ed) and helper words (was, did, had) may make it easier (Waxman et al., 2013).

An alternative explanation considers the entire social context: Playing with a variety of toys and learning about dozens of objects are routine in North America, whereas East Asian cultures emphasize human interactions—specifically, how one person responds to another. Accordingly, North American infants are expected to name many objects, whereas Asian infants are expected to act on objects and respond to people.

Thus, Chinese toddlers might learn the equivalent of come, play, love, carry, run, and so on earlier. Indeed, 14-month-olds in Chinese-speaking families learn some new words more readily than do their English-speaking peers, with the Chinese infants better able to learn action words than object labels (Chan et al., 2011).

A simpler explanation is that young children are sensitive to sounds. Verbs are learned more easily if they sound like the action (Imai et al., 2008), and such verbs are more common in some languages than others.

English does not have many onomatopoeic verbs, which makes verb-learning difficult. (Jump, kiss, and poop—all learned early on—are exceptions.) When the same word could be a noun or a verb, English-speaking mothers say them differently: Kiss, for instance, is spoken with more emphasis as a noun than a verb, so babies learn the noun before the verb (Conwell & Morgan, 2012). The infant’s focus on sounds explains why many toddlers who have never been on a farm know that cows “moo” and ducks “quack.”

Every language has some words and concepts that are difficult. English-speaking infants confuse before and after; Dutch-speaking infants misuse out when it refers to taking off clothes; Korean-speaking infants need to learn two meanings of in (Mandler, 2004). Learning adjectives is easier in Italian and Spanish than in English or French because of patterns in those languages (Waxman & Lidz, 2006). Specifically, adjectives can stand by themselves without the nouns. If I want a blue cup from a group of multicolored cups, I would ask for “a blue cup” or “a blue one” in English but simply “uno azul” (a blue) in Spanish. Despite such variations, in every language, infants rapidly acquire both vocabulary and grammar.

Grammar includes all the methods that languages use to communicate meaning. Word order, prefixes, suffixes, intonation, verb forms, pronouns and negations, prepositions and articles—all of these are aspects of grammar. Grammar can be discerned in holophrases, as one word can be spoken differently depending on meaning. However, grammar becomes essential when babies begin to use two-word combinations (Bremner & Wachs, 2010). That typically happens between 18 and 24 months.

192

193

For example, “Baby cry” and “More juice” follow grammatical word order. No child asks, “Juice more,” and even toddlers know that “cry baby” is not the same as “baby cry.” By age 2, children combine three words. English grammar uses subject–verb–object order. For example, toddlers say “Mommy read book,” rather than any of the five other possible sequences of those three words.

Children’s proficiency in grammar correlates with the length of their sentences, which is why in every language mean length of utterance (MLU) is considered an accurate way to measure a child’s language progress (e.g., Miyata et al., 2013). The child who says “Baby is crying” is advanced compared with the child who says “Baby crying” or simply the holophrase “Baby.” (See Visualizing Development, p. 192.)

Young children can master two languages, not just one. Children are statisticians: They implicitly track the number of words and phrases and learn those expressed most often, in one, two, or more languages (Johnson & Tyler, 2010). (Developmental Link: Bilingual learning is discussed in detail in Chapter 9.) The toddler who often hears two languages will soon speak two languages.

Worldwide, people who are not yet 2 years old already speak their native language, or two or three languages if that is what they hear. They can express hopes, fears, and memories, and they continue to learn rapidly: All teenagers communicate with nuanced words and gestures, and some compose lyrics or deliver orations that move thousands of their co-linguists. These impressive accomplishments raise the question: How is language learned so easily and so well?

Answers come from three schools of thought, each connected to a theory introduced in Chapter 2: behaviorism, sociocultural theory, and evolutionary psychology. The first theory says that infants are directly taught, the second that social impulses propel infants to communicate, and the third that infants understand language because of brain advances several millennia ago that allowed survival of our species.

The seeds of the first perspective were planted more than 50 years ago, when the dominant theory in North American psychology was behaviorism, or learning theory. The essential idea was that all learning is acquired, step-by-step, through association and reinforcement. Just as Pavlov’s dogs learned to associate sound with food, infants may associate objects with words, especially if reinforcement occurs.

B. F. Skinner (1957) noticed that spontaneous babbling is usually reinforced. Typically, every time the baby says “ma-ma-ma-ma,” a grinning mother appears, repeating the sound and showering the baby with attention, praise, and perhaps food. The baby learns affordances and repeats “ma-ma-ma-ma” when lonely or hungry; through operant conditioning, talking begins.

Skinner believed that most parents are excellent instructors, responding to their infants’ gestures and sounds, thus reinforcing speech (Saxton, 2010). Even in preliterate societies, parents use child-directed speech, responding quickly with high pitch, short sentences, stressed nouns, and simple grammar—exactly the techniques that behaviorists would recommend. In every culture that has been studied, those infants who learn language faster have parents who speak to them often. Few parents know the theory of behaviorism, but many use behaviorist techniques that Skinner would recommend, because these methods succeed (Tamis-LeMonda et al., 2014).

194

The core ideas of this theory are the following:

Behaviorists note that some 3-year-olds converse in elaborate sentences; others just barely put one simple word with another. Such variations correlate with the amount of language each child has heard. Parents of the most verbal children teach language throughout infancy—singing, explaining, listening, responding, and reading to their children every day, even before age 1 (Forget-Dubois et al., 2009) (see Figure 6.2).

In one detailed U.S. study, researchers analyzed a 10-minute sample of the language that mothers used with their 9-month-old infants (Tamis-LeMonda et al., 2001). All the mothers were middle class, from the same nation (to control for SES and culture). One mother never imitated her infant’s babbling; another mother imitated 21 times, babbling back in conversation. All mothers described things or actions (e.g., “That is a spoon you are holding—spoon”), but one offered only 4 descriptions while another gave 33 in the 10-minute segment.

The frequency of maternal responsiveness at 9 months predicted language acquisition at 17 months. It was not that noisy infants, whose genes might soon make them verbal, elicited more talk. Some quiet infants had mothers who frequently suggested play activities, described things, and asked questions. Quiet infants with talkative mothers usually became more verbal toddlers than their peers.

According to behaviorists, if adults want children who speak, understand, and (later) read well, they must talk to their infants. A recent application of this theory comes from commercial videos, designed to advance toddlers’ vocabulary. Typically, such videos use repetition and attention-grabbing measures (sound, tone, color) to encourage babies to learn new words (Vaala et al., 2010). Such videos, and Skinner’s theories, have come under attack from many developmentalists, as explained in the following Opposing Perspectives feature.

195

The second theory is called social-pragmatic. It arises from the sociocultural reason for language: communication. According to this perspective, infants communicate because humans are social beings, dependent on one another for survival and joy. Each culture has practices that further social interaction; talking is one such practice. Thus, all infants (and no chimpanzees) master words and grammar to join the social world in which they find themselves (Tomasello & Herrmann, 2010).

196

According to this perspective, it is the emotional messages of speech, not the words, that propel communication. In one study, people who had never heard English (Shuar hunter-gatherers living in isolation near the Andes Mountains) listened to tapes of North American mothers talking to their babies. The Shuar successfully distinguished speech conveying comfort, approval, attention, and prohibition, without knowing any of the words (Bryant & Barrett, 2007). This study suggests that the social content of speech is universal; therefore, since babies are social creatures, they learn whatever specifics their culture provides.

Suppose an 18-month-old is playing with an unnamed toy and an adult utters a word. Does the child connect that word to the toy? A behaviorist, learning-by-association prediction would be yes, but the answer is no. In an experiment, when toddlers played with a fascinating toy and adults said a word, the toddlers looked up, figured out what the adult was looking at, and assigned the new word to that, not to the fascinating toy (Baldwin, 1993). This supports theory two: The toddlers wanted to know what the adults intended.

Evidence for social learning comes from educational programs for children. Many 1-year-olds enjoy watching television and videos, as the Opposing Perspectives feature on page 195 explains, but they learn best when adults are actively involved in teaching. In a controlled experiment, 1-year-olds learned vocabulary much better when someone taught them directly than when the same person gave the same lesson on video (Roseberry et al., 2009).

According to theory two, then, social impulses, not explicit teaching, lead infants to learn language. According to this theory, people differ from the great apes in that they are social, driven to communicate (Tomasello & Herrmann, 2010).

A third theory holds that language learning is genetically programmed to begin at a certain age; adults need not teach it (theory one), nor is it a by-product of social interaction (theory two). Instead, it arises from the universal genetic impulse to imitate. Languages have been developed to take advantage of this maturation process. For example, English has articles (the, an, a) that signal to the baby that the next word will be the name of an object, and since babies have “an innate base” that primes them to learn, such articles facilitate learning nouns (Shi, 2014, p. 9).

As already explained in the research on memory, infants and toddlers observe what they see and they apply it—not slavishly but according to their own concepts and intentions, which develop as the brain matures. Theory three proposes that this is exactly what they do with the language they hear (Saxton, 2010).

This theory is buttressed by research that finds that variations in children’s language ability correlate with differences in brain activity and perceptual ability, evident months before the first words are spoken and apart from the particulars of parental input (Cristia et al., 2014). Some 5-year-olds are far more verbal than others because they were born to be so.

197

This perspective began soon after Skinner proposed his theory of verbal learning. Noam Chomsky (1968, 1980) and his followers felt that language is too complex to be mastered merely through step-by-step conditioning. Although behaviorists focus on variations among children in vocabulary size, Chomsky focused on similarities in language acquisition—the universals, not the differences.

Noting that all young children master basic grammar according to a schedule, Chomsky cited this universal grammar as evidence that humans are born with a mental structure that prepares them to seek some elements of human language. For example, everywhere, a raised tone indicates a question, and infants prefer questions to declarative statements (Soderstrom et al., 2011). This suggests that infants are wired to have conversations, and caregivers universally ask them questions long before they can answer back.

Chomsky labeled this hypothesized mental structure the language acquisition device (LAD). The LAD enables children, as their brains develop, to derive the rules of grammar quickly and effectively from the speech they hear every day, regardless of whether their native language is English, Thai, or Urdu. On their part, adults, because of their own LAD, instinctively help children learn whatever superficial differences appear between one language and another.

Other scholars agree with Chomsky that all infants are primed, naturally, to understand and speak whatever language they hear. They are eager learners, and speech becomes one more manifestation of neurological maturation (Wagner & Lakusta, 2009). This idea does not strip languages and cultures of their differences in sounds, grammar, and almost everything else, but the basic idea is that “language is a window on human nature, exposing deep and universal features of our thoughts and feelings” (Pinker, 2007, p. 148).

According to theory three, language is experience-expectant, as the developing brain quickly and efficiently connects neurons to support whichever language the infant hears. Because of this experience expectancy, the various languages of the world are all logical, coherent, and systematic. Then some experience-dependent learning occurs as each brain adjusts to a particular language.

Research supports this perspective as well. As you remember, newborns are primed to listen to speech (Vouloumanos & Werker, 2007), and all infants babble ma-ma and da-da sounds (not yet referring to mother or father). No reinforcement or teaching is required; all a baby needs is time, and that will allow dendrites to grow, mouth muscles to strengthen, neurons to connect, and speech to be heard. This theory might explain why poets put together phrases that they have never heard to produce novel understanding, and why people hear words in their dreams that make no sense. Thus, the language impulse may arise from the brain, not from other people.

Nature even provides for deaf infants. All 6-month-olds, hearing or not, prefer to look at sign language over nonlinguistic pantomime. For hearing infants, this preference disappears by 10 months because their affinity for gestural language is not necessary for communication (Krentz & Corina, 2008). Deaf infants are signing by then, which is their particular expression of LAD, a universal impulse.

Which of these three perspectives is correct? Perhaps all of them are true, to some extent. In one monograph that included details and results of 12 experiments, the authors presented a hybrid (which literally means “a new creature, formed by combining other living things”) of previous theories (Hollich et al., 2000). Since infants learn language to do numerous things—to indicate intention, call objects by name, put words together, talk to family members, sing to themselves, express wishes, remember the past, and much more—some aspects of language learning are best explained by one theory at one age and other aspects by another theory at another age.

198

Although originally developed to explain acquisition of first words, mostly nouns, this theory also explains learning verbs: Perceptual, social, and linguistic abilities combine to make that possible (Golinkoff & Hirsh-Pasek, 2008). Linguists seek to understand how most children acquire more than one language; it seems that many strategies help (Canagarajah & Wurr, 2011).

One study supporting the hybrid theory began, as did the study previously mentioned, with infants looking at pairs of objects that they had never seen and never heard named. One of each pair was fascinating to babies and the other was boring, specifically “a blue sparkle wand … [paired with] a white cabinet latch … a red, green, and pink party clacker … [paired with] a beige bottle opener” (Pruden et al., 2006, p. 267). The experimenter said a made-up name (not an actual word), and then the infants were tested to see whether they assigned the new word to the object that had the experimenter’s attention (the dull one) or to the one that was interesting to them.

Unlike the similar study already described, which involved 18-month-olds, the participants in this one were 10-month-olds. They responded differently than the older infants did. The 10-month-olds seemed to assign the word to the fascinating object, not the dull one. These researchers’ interpretation was that how language is learned depends on the age of the child as well as on the particular circumstances. Behaviorism may work for young children, social learning for slightly older ones: “The perceptually driven 10-month-old becomes the socially aware 19-month-old” (Pruden et al., 2006, p. 278).

Current thinking is that children are not exclusively social learners or behaviorists and that learning a new word or grammar form is not an all-or-none accomplishment. Instead, partial learning occurs: A lack of evident mastery of a word makes it easier to learn that word or a related word later on (Yurovsky et al., 2014).

This may be easier to understand with an example. Suppose a 1-year-old meets an unfamiliar child named Tom and fails to say his name or wave “bye-bye Tom” when asked. That might be considered failure—Chomsky might say the child was not ready, Skinner might say the child was not sufficiently reinforced, social learning theorists might say that Tom was not socially important.

But then, a week later, the child might see Tom again, hear that his name is Tom, and immediately say “Tom.” The likely explanation is that partial learning occurred the first time, so the second time it became evident. Such experiences are common: A toddler might surprise everyone by saying a word that was heard earlier. Learning is more likely if all three factors (reinforcement, social impulses, maturation) combine.

After intensive study, yet another group of scientists also endorsed a hybrid theory, concluding that “multiple attentional, social, and linguistic cues” contribute to early language (Tsao et al., 2004, p. 1081). It makes logical and practical sense for nature to provide several paths toward language learning and for various theorists to emphasize one or another of them (Sebastián-Gallés, 2007).

It also seems that some children learn better one way and others another way (Goodman et al., 2008), and that families and cultures vary in how they teach. Since every human must learn language, nature allows diversity in specifics so that the goal is always attained. Ideally, parents talk often to their infants (theory one), encourage social interaction (theory two), and appreciate the innate abilities of the child (theory three).

199

As one expert concludes:

our best hope for unraveling some of the mysteries of language acquisition rests with approaches that incorporate multiple factors, that is, with approaches that incorporate not only some explicit linguistic model, but also the full range of biological, cultural, and psycholinguistic processes involved.

[Tomasello, 2006, pp. 292–293]

The idea that every theory is correct may seem idealistic. However, many scientists who are working on extending and interpreting research on language acquisition arrive at a similar conclusion. They contend that language learning is neither the direct product of repeated input (behaviorism) nor the result of a specific human neurological capacity (LAD). Rather, from an evolutionary perspective, “different elements of the language apparatus may have evolved in different ways,” and thus, a “piecemeal and empirical” approach is needed (Marcus & Rabagliati, 2009, p. 281). In other words, no single theory explains how babies learn language: Humans accomplish this feat in many ways.

What conclusion can we draw from all the research on infant cognition? It is clear that infants are active learners of language and concepts and that they seek to experiment with objects and find ways to achieve their goals. This is the cognitive version of the biosocial developments noted in Chapter 5, that babies strive to roll over, crawl, walk, and so on as soon as they can. (See Visualizing Development, p. 192.)

200