This article describes an elegant study. I found the 7 percent addiction-susceptible figure interestingly similar to the 10 percent of people who drink alcohol who become addicted. I wonder if similar percentages of other species are impulsive and vulnerable.

Ellen Waggener
Poughkeepsie, N.Y.

Use up and down arrow keys to explore.Use right arrow key to move into the list.Use left arrow key to move back to the parent list.Use tab key to enter the current list item.Use escape to exit the menu.Use the Shift key with the Tab key to tab back to the search input.