Tired, overwhelmed women often feel as if having a baby causes their minds to turn to mush. Not so. In her book, The Mommy Brain, Katherine Ellison cites research showing motherhood makes women smarter and more mentally agile.

There is no more challenging time in a woman's life than when she has a baby, says Ellison, and human evolution has ensured that she is well equipped to handle it. Alert, efficient and empathetic, a mother's mind is designed to make the species survive.

Although some of the benefits, such as heightened sensory awareness, seem to last only as long as it takes the baby to grow up, others may be lifelong. According to Ellison, the mental dexterity that mothers gain from raising their kids may translate permanently into greater empathy and assertiveness.

A combination of motivation, practice and hormones gives mothers intellectual strengths they may have never had before.

Mom's new traits, why she's different, and what's happening:

Face Reading

• Mothers of toddlers are better at reading facial expressions than women who don't have children.
• Mothers develop attention to tiny changes in expression and body language in their kids, actually expanding the brain's circuits related to empathy.

Multitasking

• Mother rats can simultaneously solve mazes and find food much more quickly than childless rats.
• During pregnancy and early motherhood, the brain is bathed in estrogen, which increases connections in the cerebral cortex that deal with attention and complex tasks.

Serenity

• Three to six months after delivery, breastfeeding mothers are less tense, less edgy and less bored.
• Mothers experience greater sensitivity to the hormone oxytocin, what anthropologist Sarah Hrdy calls "the endocrinological equivalent of candlelight, soft music and a glass of wine."

Fearlessness

• Rat moms will venture into broad daylight; human moms will swim across the Rio Grande.
• Elevated levels of prolactin, the "parenting" hormone, makes mothers willing to risk their lives for their babies.