It all starts by looking a baby right in the eyes

Here is a book that gives new meaning to the old saying, "The hand that rocks the cradle rules the world." Its authors, one a psychiatrist and the other a psychologist and philosopher, have teamed up to tackle the momentous question of how humans developed language. Fearing not to challenge some of the heavyweights of modern science, from Jean Piaget to Noam Chomsky and Steven Pinker, they present their own theory: The development of language is connected primarily with affect rather than cognition, with the emotional learning that occurs in infants in the arms of those who love them. That is, language is rooted not in genes, not in the wiring of brains, but in behaviors we have learned over millenniums.

Phrases like "emotional intelligence" and "the feeling brain" sound less oxymoronic today than they did before they appeared in the titles of groundbreaking works by Daniel Goleman and, more recently, Antonio Damasio. But in "The First Idea," Stanley Greenspan and Stuart Shanker contend that "emotional intelligence," as it is coming to be understood, is only one of the "roots and branches" of intelligence itself. "The trunk," they argue, is a set of abilities they refer to as the "functional-emotional developmental capacities."

The critical concept in "The First Idea" is what the authors call "co-regulated emotional signaling." By this they mean the affectionate back-and-forth between baby and caregiver. Mom and Baby make eye contact, and when Mom smiles at Baby, Baby smiles back.

It would be simplistic to say that the authors see games of peekaboo and patty-cake as the foundations of civilization - but it would not be completely wide of the mark. It is just this sort of nonverbal "conversation," the authors argue, that was essential to the development of language among early humans and remains essential to each child's learning to talk today.

Later on, children progress to "shared social problem solving," by which the authors mean such things as a toddler gesturing toward the cookie jar and getting her father to understand what she wants. Even before language, there is a vocabulary of gesture and vocalization, and a skill of reading facial expression, gestures, and body language of other people, of falling into their rhythms, that very young children develop.

Mastery of these helps children regulate or modulate their emotions; they are able to point to the cookie jar instead of just screaming and leaving their parents to guess what they want, for instance. And this regulation leads to the formation of "ideas," in the special sense the authors use: "An idea is an image that has been freed from a fixed, immediate action and is invested with affects or emotions (i.e., intent) to give it meaning." Mental development is about "taming emotions into signals."

Putting it in more concrete terms, the authors offer as an example a child who lights up at the prospect of going outdoors - but knows she must get her shoes on first. "The child learns how to say 'shoe' in the context of her excitement at being able to go outside and explore a whole new world. Otherwise, the incentive to learn the word is slight."

Lived emotional experience is key to language learning, the authors suggest. "Mathematicians and physicists may manipulate abstruse symbols representing space, time, and quantity, but they first understood those entities as tiny children wanting a far-away toy, or waiting for juice, or counting cookies. The grown-up genius, like the adventurous child, forms ideas through playful explorations in the imagination, only later translated into the rigor of mathematics."

The authors can't be faulted for lack of ambition. Along with their theory to explain the evolution of human language, they also have a thesis based on this theory for explaining autism - and a method of treatment. They provide a short course in primatology as they present their case for certain kinds of intelligence in chimpanzees, bonobos, and other apes.

For any readers who missed Soc/Anthro 101, they also provide an introduction to the salient points of the work of Franz Boas, Max Weber, Claude Lévi-Strauss, Emil Durkheim, Pierre Bourdieu, and others. Throughout, the authors summarize the theories of those they take issue with, and explain why they do so, in a respectful way that inspires confidence in their fairness.

They provide an overview of the history of science, and the history of history itself, starting with Herodotus and Thucydides. After taking issue with Descartes early on for his mechanistic view of the human mind and the development of language, they pay him homage as the man who brought the ideas of the 17th-century scientific revolution to bear on the human mind itself. He was a great thinker on the subject of thinking who "established reason as a revolutionary force," they note.

This book is not so much a stroll in the park as an invigorating hike in the woods. But the trail is well marked, with many appealing stopping points along the way. The general reader who invests time and energy in "The First Idea" will be amply rewarded.

• Ruth Walker is the Monitor's chief copy editor.

1. Lower primates develop attention through shared gaze and back-and-forth vocalizations during play and feeding.

2. Our primate ancestors begin relating through subtle back-and-forth emotional interactions between caregivers and infants.

3. Australopithecines master two-way purposeful emotional interaction such as telling a story with gestures (5.3 - 1.4 millions years ago).

4. Early humans engage in shared problem solving, such as coordinating a hunt through body movements and facial expressions (2 - 0.4 million years ago).

5. Archaic humans acquire symbolic and linguistic abilities through complex interactions involving presymbolic communication (600,000 - 100,000 years ago).

6. Anatomically modern humans begin connecting ideas together and thinking logically (130,000 years ago - present).

7. Modern humans begin to think about thinking.