"Despite the fact that it took our ancestors about 2,000 years to develop an alphabetic code, children are regularly expected to crack this code in about 2,000 days (that is, by six or seven years of age), or they will run afoul of the whole educational structure -- teachers, principals, family, and peers. If reading is not acquired on society's schedule, these suddenly disinherited children will never feel the same about themselves. They will have learned they are different, and no one ever tells them that evolutionarily, this might be for a good reason."

So writes Maryanne Wolf, professor of child development at Tufts University and director of the Center for Reading and Language Research. Her book, "Proust and the Squid: the story and science of the reading brain," is an exploration of just what the brain is up to when we learn -- or don't learn -- the skill of reading.

Her fundamental insight is this: we were never born to read. There is no one part of the brain that was wired to handle it.

Genetic scientists have pinpointed (through the evidence of mitochondrial DNA) the arrival of Eve around 170,000 years ago. But reading -- the ability to decode scratches as language -- is a far more recent invention. Probably, it made its appearance no sooner than about 10,000 years ago.

This means that reading is not innate. It is a learned behavior. Brain research -- the ability to watch which parts of the brain light up as we read and understand -- has revealed that it is also complex.

Wolf offers up a lot of surprises. Get this: you use different parts of the brain to read Chinese than you do to read English.

That makes sense once you think about it. Chinese is ideographic, based more on abtract symbols than on letters standing for sounds. So decoding Chinese uses parts of the brain originally dedicated to the processing of visual imagery; reading English repurposes regions of the brain that process sound.

But English is not consistently phonetic. Other languages -- Finnish, German, Romance languages -- are more regular, that is, the letters match up better with the sounds. In those languages, children are pushed, sooner, to become fluent -- to read smoothly and quickly.

Each language has people who struggle with reading. But those reading problems are different according to the language, and manifest themselves at different ages. There is no one explanation for the trouble.

Wolf ultimately makes two points.

First, the skill of literacy is a marvel of neurological interplay. It activates all kinds of areas of the brain to make sense of writing. And when that skill is mastered, fluency gives us the time to think ahead, to think new thoughts, to grow in ways we simply could not grow otherwise. It's magic.

Second, but we are not all wired the same. Again, every culture has people who struggle with learning to read. But they are not "disabled." Famous dyslexics include Leonardo da Vinci and Tom Edison.

When dyslexics do learn to read, they literally have to build entirely different neural paths than the rest of us. Generally, they seem to use more of their right side of the brain, which isn't really set up for the precisely timed and synchronized tasks required for reading fluency.

But that kind of thinking has other compensations. In an evolutionary sense, we must need those kinds of brains. Reading is an important skill -- but our species depends on others, too.

In short, "diversity" doesn't just refer to differences in skin color or culture. Even within a single family, it can refer to fundamental differences in the circuitry of our minds.