Now that the 2000-aughts are coming to a whimpering end we can look forward to the nostalgic retrospectives, most of which will no doubt focus on the end of the bubble, or series of bubbles. It was the housing bubble that brought us down (we took a bath), and amid the talk of bubbles we may think of the baby bubble that was subdominant in the lifestyle pages kitty-corner from the business pages. If you subscribed to Cookie or Brain, Child, groused about "opt-out revolutions," double-wide Bugaboos and the cost of Bisphenol-free bottles in the comment streams of mommy blogs, then you know as a member of the tribe of nesters, you had your own little branchlet of English: a jargon.

Jargon or no, what has evolved to suit the requirements of grown-ups in an information-rich world is Occam’s-razoresque: short sentences, simple vocabulary, logical progression. Parents who want their infants to learn language need a lot more than this. They need "motherese," that high-pitched sing-song dialect that puts everything in the third person and diminutizes it. ("MOMmy WUVS her lil PUMkin!") It is serious business, motherese, a term coined by Dean Falk, a professor of anthropology at Florida State University. It is "spoken music" whose melody exaggerates the "statistical and prosodic regularities in language input that lead to phonetic and word learning," which, according to speech scientist Patricia Kuhl, is key to early language acquisition. I learned a bit about this when Early Intervention sent a speech therapist for my taciturn 2-year-old. I adopted her extreme flutelike tones, and lo, within a couple of months my son went from a twenty-word vocabulary to six-word sentences. He wasn’t the dumb one; I was, for not deploying motherese with more gusto.

Falk claims that motherese is the key to the evolution of human language. In her new book, Finding Our Tongues: Mothers, Infants, and the Origins of Language (Basic; $26.95), she sets forth the theory that the first protolanguage evolved from the vocalizations between hominins and their babies, which unlike the babies of other primates could not grasp the mother and periodically had to be laid aside so that the mother could forage for food. Falk calls it the "putting the baby down" hypothesis. The child’s distress would be allayed by the mother’s voice, which amounted to an extension of her arms: vocal contact. (Animals, too, use vocalizations to regulate distances.) Moreover, language seems to be "built from the networks in the brain that were originally important for reaching and grasping," which makes our idiom of mental grasping less metaphorical than literal. The mother’s voice is really that other pair of hands she always needed.

Chimps are more likely to vocalize when sad than when happy. The idea that language evolved to mend a rift that caused a mother and infant to become prematurely part of each other’s "external world" is not so very distant from the Orpheus myth, wherein the trauma of separation from Eurydice becomes the genesis of poetry. In the end, Orpheus’ dismembered head babbles its song down a stream. Babbling, of course, is the precursor to language and–in one of the most intriguing facts in the book–so is crying a precursor to babbling. Researchers have identified "melody arcs" in infant crying, prosodic patterns that get more complex as the baby grows. If loss, song and language are truly intertwined, Falk’s is a new twist on an old myth.

The origin of language is a hot topic–contentious and impossible to prove, but hot. Falk points out that anthropologists have a blind spot where women and babies are concerned: it’s always assumed that the hunters and their toolmaking technologies drive evolution, but in the case of language the childcare hypothesis is more grounded in data than others (like the evidence, provided by John Newman of the National Institutes of Health, that the language circuits in the brain for mother-infant communication developed early). Nevertheless, it isn’t all sexism: there’s fundamental disagreement as to whether language acquisition is based in memory or linguistic universals. Falk follows the constructivists: the infant listens, and through repetition and practice learns to parse the speech stream. Theoretically, this is more mimetic than innatist.

Derek Bickerton, a professor emeritus at the University of Hawaii, splits the difference a bit. In his new book, Adam’s Tongue: How Humans Made Language, How Language Made Humans (Farrar, Straus and Giroux; $27.50), he posits that language derived from signals between scavenging hominins looking to pool resources. But it wasn’t continuous with other animal vocalizations. It was an evolutionary leap, opening up an "ecological niche" per the new theory of niche construction, whereby species get to participate, through modifications in behavior, in their own development. As language progressed, it took on a life of its own, incorporating more arbitrariness, more complexity, more displacement. An endlessly recursive, autocatalytic system, it became the breakaway mechanism of our evolution. Its feedback made us smarter.

"Motherese" versus "Adam’s tongue" sets up an all-too-easy binary, but the gendered style differences don’t stop there. Bickerton addresses the reader with imperatives, commanding us with thought experiments replete with numbers: "So think of any ten words or signs that, singly or in combination, would increase the survival chances and/or procreative capacities of their user." You have thirty seconds. Go!

Bickerton’s point is that language would never have developed beyond those first ten (or less) words if they didn’t prove uniquely useful at that moment in evolution. And because he doesn’t believe that animal communication systems are continuous with human language, he disagrees with Falk’s hypothesis. It "founders when we start asking how meaning crept in." In other words, the leap from prosody to symbols in motherese is totally glossed over.

Instead, the conditions for language development might look something like this: our ancestors, high-end scavengers, had to recruit individuals to form a hand-ax-wielding group and take control of large carcasses from other beasts. If the carcass was out of sight and smell of the others, the hand-ax wielders would have needed some way to signal an abstraction and persuade each other to cooperate. It wouldn’t take more than ten words–probably less. But it is a sufficient explanation for how symbols were first born.

Bickerton’s scenario for the genesis of language seems to drain the poetry from it. The drab thought of our ancestors–hunger on the brain–hacking away at a deinotherium just doesn’t carry the same frisson as Falk’s theory, wherein motherese not only stimulates language but theory of mind–the recognition of intention, of personhood, in someone else. But Bickerton’s theory may simply substitute another poetic, that of the uncanny, for Falk’s orphic one. William Burroughs thought language was a virus from outer space; Jack Spicer thought poetry came from Martian signals. Likewise, language "isn’t just unique–it’s unnatural," Bickerton declares. We’ve given life to an unnatural being, which rebirthed us in turn. We might well ask: what child is this?