Did blonde hair spread during the Ice Age? Peter Frost, a researcher at the University of St. Andrew's, says fair coloring was rare in Europe until the Pleistocene. Men were also scarce due to a high death rate on hunting expeditions. The unbalanced sex ratio may have allowed men to be choosier when selecting a mate. Frost believes men were attracted to rare traits, giving rise to today's fair-haired Swedish models.

Cramming for a test? You may want to postpone dinner. Ghrelin, a hunger hormone produced by empty stomachs, enhances learning in the short term, at least in rats. Ghrelin speeds communication in the hippocampus, a brain region associated with spatial memory. The effect may have helped our human ancestors hunt and forage on while famished. So should you fast before strenuous mental activities? It's definitely a strategy worth considering, says Yale University researcher Tamas Horvath.

Eight percent of prospective parents would choose their child's sex if given the option.

Half of Americans worry that stress is wrecking their mental and physical health, but very few are taking steps to tackle the problem. One in four Americans say they overeat to comfort themselves, while 25 percent of those who describe themselves as "very concerned" about stress turn to cigarettes for relief of frustration and anxiety.

Trying to rouse kids off the couch? When it comes to fitness, one motivator outshines all others: personal fulfillment. Preaching weight loss as the goal of exercise is likely to backfire.

Text-messaging makes for intimate friendships. Pals who only communicate face-to-face have less chummy relationships than those who also let their fingers do the talking, according to a Japanese study. Most people who text-message from their mobile phones tend to do so with only half of their friends.

Black couples are at higher risk for divorce than white couples, but religion is a buffer against breakups. Black couples who attend religious services tend to stay together, regardless of the importance of faith in their family or how frequently they attend services.

Rover may be your best friend, but in crisis times his closest pal is likely to be another dog. A study of thunderstorm-phobic dogs found that no amount of cooing or stroking by even the most sympathetic owner can soothe a stressed-out pooch. The best remedy for storm anxiety, say Penn State researchers, is the company of other canines.