What makes food delicious? The Food Issue of Scientific American offers a scientific answer.

Taste and flavor are more complex than a confluence of the five tastes - sweet, salty, bitter, sour and umami - and the sense of taste isn't limited to the mouth. Scientists have found taste receptors all over the body, including the small intestine, which can detect sweet flavors, and the nose and throat, which can sense bitterness.

Auditory and visual cues, such as the sound of chomping down on a crunchy potato chip or the color of a dinner plate, and the opinions of our mothers and friends also affect whether we find something delicious. "It's mental as much as chemical," one of the articles says.

The special issue also includes pieces about brain research suggesting that obesity is an addiction; the 2million- year history of processed food; whether different types of calories (carbs vs. fat, say) make the difference in weight gain; and how barbecue (or fire, anyway) was vital to human evolution by allowing us to cook food, which made it easier to digest and thus get the calories we needed for our large brains to grow.

"Cracked Open" by Miriam Zoll In vitro fertilization. Surrogate births. Womb transplants. In an age when one of every eight U.S. couples experiences infertility, according to the National Survey of Family Growth, modern science promises to make the impossible possible.

But just because such high- tech "fertility feats" are becoming more commonplace doesn't mean there is always a happy ending, argues Miriam Zoll in the memoir "Cracked Open: Liberty, Fertility and the Pursuit of High-Tech Babies."

Zoll details her and her husband's experience with four IVF cycles, all of which failed, and two donor- egg cycles, which also failed after both donors were found to be infertile.

Zoll writes that she "grew up with dazzling front-page stories heralding the marvels of test- tube babies, frozen sperm, and egg donors; stories that helped paint the illusion that we could forget about our biological clocks and have a happy family life after - not necessarily before or during - the workplace promotions."

But, Zoll writes, the reality of her attempts to have a baby in her late 30s and 40s didn't match the hype.

The book takes a critical look at the fertility industry, the failure rate of later pregnancies and what Zoll calls the "epidemic of misinformation" in the media about delaying parenthood.

"They told us that we didn't have to rush to have kids," Zoll recalls a friend telling her. "They told us it was okay to wait, and in the end it's not."