19. The purpose of non-REM sleep is even more mysterious. The new experiments, such

69. This near-tripling of oil prices calls up scary memories of the 1973 oil shock, when prices quadrupled, and 1979-1980, when they also almost tripled. 

70. In just one generation, millions of mothers have gone to work, transforming basic family economics.

68. Again, differences between people and the opportunity for natural selection to take advantage of it have diminished.

66. What is odd is that they have perhaps most benefited from ambition — if not always their own then that of their parents and grandparents. 

67. This success, coupled with later research showing that memory itself is not genetically determined, led Ericsson to conclude that the act of memorizing is more of a cognitive exercise than an intuitive one. 

64. Strengthening economic growth, at the same time as winter grips the northern hemisphere, could push the price higher still in the short term.

65. But it is hardly inevitable that companies on the Web will need to resort to push strategies to make money. 

63. It is not possible to determine whether both continents are moving in opposite directions or whether one continent is stationary and the other is drifting away from it.

61. Proper, scientific study of the impacts of dams and of the cost and benefits of controlling water can help to resolve these conflicts.

62. The coming of age of the postwar baby boom and an entry of women into the male-dominated job market have limited the opportunities of teenagers who are already questioning the heavy personal sacrifices involved in climbing Japan's rigid social ladder to good schools and jobs.